Merge branch 'lukas/erts/poll-thread/OTP-14346'

* lukas/erts/poll-thread/OTP-14346: (25 commits)
  erts: Trigger ready events when erts_io_control fails
  erts: enif_select steal test
  kernel: Rewrite gen_udp_SUITE:read_packet tc
  erts: disable kernel-poll on OS X vsn < 16
  erts: Fix msacc testcase with new poll-thread
  erts: Add testcases to test IOp and IOt options
  erts: get_internal_state(check_io_debug) now prints to error_logger
  erts: Remove eager check io
  erts: Move all I/O polling to a seperate thread
  erts: Fix smp_select testcase to use ERL_DRV_USE
  erts: Fix msacc unmanaged state counter
  erts: Optimize port_task quick allocator
  erts: Add ERTS_THR_PREF_QUICK_ALLOC_IMPL
  erts: Update suspend of scheduler to handle multiple pollsets
  erts: Add multiple poll sets
  erts: Some code cleanup for gdb to work better
  erts: temp_alloc can no longer be disabled
  erts: Refactor check_io to use one static struct
  erts: Replace check_io spinlock with lock-less list insertion
  erts: Add number of enif_select's to check_io_debug
  ...

46 files changed, 3769 insertions, 5352 deletions

diff --git a/erts/emulator/Makefile.in b/erts/emulator/Makefile.in
index 02a9a9a93b..915cad4e18 100644
--- a/erts/emulator/Makefile.in
+++ b/erts/emulator/Makefile.in
@@ -251,7 +251,7 @@ endif
 HIPEBEAMLDFLAGS=$($(ARCH)BEAMLDFLAGS)
 endif
 
-ERTS_ENABLE_KERNEL_POLL=@ERTS_ENABLE_KERNEL_POLL@
+ERTS_BUILD_FALLBACK_POLL=@ERTS_BUILD_FALLBACK_POLL@
 
 #
 #
@@ -928,17 +928,15 @@ $(STATIC_NIF_LIBS) $(STATIC_DRIVER_LIBS):
 	echo "=== Leaving lib after making static libs"
 endif
 
-ifeq ($(ERTS_ENABLE_KERNEL_POLL),yes)
+ifeq ($(ERTS_BUILD_FALLBACK_POLL),yes)
 OS_OBJS += 	$(OBJDIR)/erl_poll.kp.o \
-		$(OBJDIR)/erl_check_io.kp.o \
-		$(OBJDIR)/erl_poll.nkp.o \
-		$(OBJDIR)/erl_check_io.nkp.o
+		$(OBJDIR)/erl_poll.nkp.o
 else
-OS_OBJS +=	$(OBJDIR)/erl_poll.o \
-		$(OBJDIR)/erl_check_io.o
+OS_OBJS +=	$(OBJDIR)/erl_poll.o
 endif
 
-OS_OBJS +=	$(OBJDIR)/erl_mseg.o \
+OS_OBJS +=	$(OBJDIR)/erl_check_io.o \
+		$(OBJDIR)/erl_mseg.o \
 		$(OBJDIR)/erl_mmap.o \
 		$(OBJDIR)/erl_$(ERLANG_OSTYPE)_sys_ddll.o \
 		$(OBJDIR)/erl_mtrace_sys_wrap.o \
@@ -1112,7 +1110,7 @@ else
 SED_PREFIX=
 endif
 
-ifeq ($(ERTS_ENABLE_KERNEL_POLL),yes)
+ifeq ($(ERTS_BUILD_FALLBACK_POLL),yes)
 SED_SUFFIX=;$(SED_REPL_POLL);$(SED_REPL_CHK_IO)
 else
 SED_SUFFIX=
diff --git a/erts/emulator/beam/erl_alloc.c b/erts/emulator/beam/erl_alloc.c
index 845cef24c7..88285d8be6 100644
--- a/erts/emulator/beam/erl_alloc.c
+++ b/erts/emulator/beam/erl_alloc.c
@@ -385,6 +385,7 @@ set_default_temp_alloc_opts(struct au_init *ip)
     SET_DEFAULT_ALLOC_OPTS(ip);
     ip->enable			= AU_ALLOC_DEFAULT_ENABLE(1);
     ip->thr_spec		= 1;
+    ip->disable_allowed         = 0;
     ip->carrier_migration_allowed = 0;
     ip->atype			= AFIT;
     ip->init.util.name_prefix	= "temp_";
@@ -644,8 +645,6 @@ erts_alloc_init(int *argc, char **argv, ErtsAllocInitOpts *eaiop)
 	= ERTS_MONITOR_SH_SIZE * sizeof(Uint);
     fix_type_sizes[ERTS_ALC_FIX_TYPE_IX(ERTS_ALC_T_NLINK_SH)]
 	= ERTS_LINK_SH_SIZE * sizeof(Uint);
-    fix_type_sizes[ERTS_ALC_FIX_TYPE_IX(ERTS_ALC_T_DRV_EV_D_STATE)]
-	= sizeof(ErtsDrvEventDataState);
     fix_type_sizes[ERTS_ALC_FIX_TYPE_IX(ERTS_ALC_T_DRV_SEL_D_STATE)]
 	= sizeof(ErtsDrvSelectDataState);
     fix_type_sizes[ERTS_ALC_FIX_TYPE_IX(ERTS_ALC_T_NIF_SEL_D_STATE)]
@@ -1494,8 +1493,7 @@ handle_args(int *argc, char **argv, erts_alc_hndl_args_init_t *init)
 	&init->ll_alloc,
 	&init->driver_alloc,
 	&init->fix_alloc,
-	&init->sl_alloc,
-	&init->temp_alloc
+	&init->sl_alloc
 	/* test_alloc not affected by +Mea??? or +Mu???  */
     };
     int aui_sz = (int) sizeof(aui)/sizeof(aui[0]);
diff --git a/erts/emulator/beam/erl_alloc.h b/erts/emulator/beam/erl_alloc.h
index c661d0b226..117f96a4ad 100644
--- a/erts/emulator/beam/erl_alloc.h
+++ b/erts/emulator/beam/erl_alloc.h
@@ -402,6 +402,32 @@ NAME##_free(TYPE *p)							\
 	erts_free(ALCT, (void *) p);					\
 }
 
+#define ERTS_THR_PREF_AUX(NAME, TYPE, PASZ)				\
+ERTS_THR_PREF_PRE_ALLOC_IMPL(NAME##_pre, TYPE, PASZ)
+
+#define ERTS_THR_PREF_QUICK_ALLOC_IMPL(NAME, TYPE, PASZ, ALCT)	        \
+ERTS_THR_PREF_AUX(NAME, TYPE, PASZ)					\
+static void								\
+init_##NAME##_alloc(int nthreads)					\
+{									\
+    init_##NAME##_pre_alloc(nthreads);			                \
+}									\
+static ERTS_INLINE TYPE *						\
+NAME##_alloc(void)							\
+{									\
+    TYPE *res = NAME##_pre_alloc();					\
+    if (!res)								\
+	res = erts_alloc(ALCT, sizeof(TYPE));				\
+    return res;								\
+}									\
+static ERTS_INLINE void							\
+NAME##_free(TYPE *p)							\
+{									\
+    if (!NAME##_pre_free(p))						\
+	erts_free(ALCT, (void *) p);					\
+}
+
+
 #ifdef DEBUG
 #define ERTS_PRE_ALLOC_SIZE(SZ) ((SZ) < 1000 ? (SZ)/10 + 10 : 100)
 #define ERTS_PRE_ALLOC_CLOBBER(P, T) memset((void *) (P), 0xfd, sizeof(T))
@@ -482,7 +508,8 @@ init_##NAME##_alloc(void)						\
 {									\
     sspa_data_##NAME##__ =						\
 	erts_sspa_create(sizeof(union erts_sspa_##NAME##__),		\
-			 ERTS_PRE_ALLOC_SIZE((PASZ)));			\
+			 ERTS_PRE_ALLOC_SIZE((PASZ)), 			\
+                         0, NULL);                                      \
 }									\
 									\
 static TYPE *								\
@@ -504,6 +531,57 @@ NAME##_free(TYPE *p)							\
 			  (char *) p);					\
 }
 
+
+#define ERTS_THR_PREF_PRE_ALLOC_IMPL(NAME, TYPE, PASZ)		        \
+union erts_sspa_##NAME##__ {						\
+    erts_sspa_blk_t next;						\
+    TYPE type;								\
+};									\
+									\
+static erts_sspa_data_t *sspa_data_##NAME##__;				\
+									\
+static void								\
+init_##NAME##_alloc(int nthreads)					\
+{									\
+    sspa_data_##NAME##__ =						\
+	erts_sspa_create(sizeof(union erts_sspa_##NAME##__),		\
+			 ERTS_PRE_ALLOC_SIZE((PASZ)),			\
+                         nthreads,                                      \
+                         #NAME);                                        \
+}									\
+                                                                        \
+void								        \
+erts_##NAME##_alloc_init_thread(void)				        \
+{									\
+    int id = erts_atomic_inc_read_nob(&sspa_data_##NAME##__->id_generator);\
+    if (id > sspa_data_##NAME##__->nthreads) {                          \
+        erts_exit(ERTS_ABORT_EXIT,                                      \
+                  "%s:%d:%s(): Too many threads for '" #NAME "'\n",     \
+                  __FILE__, __LINE__, __func__);                        \
+    }                                                                   \
+    erts_tsd_set(sspa_data_##NAME##__->tsd_key, (void*)(SWord)id);      \
+}									\
+									\
+static TYPE *								\
+NAME##_alloc(void)							\
+{									\
+    int id = (int)(SWord)erts_tsd_get(sspa_data_##NAME##__->tsd_key);   \
+    if (id == 0)                                                        \
+        return NULL;                                                    \
+    return (TYPE *) erts_sspa_alloc(sspa_data_##NAME##__,		\
+                                    id-1);		                \
+}									\
+									\
+static int								\
+NAME##_free(TYPE *p)							\
+{									\
+    int id = (int)(SWord)erts_tsd_get(sspa_data_##NAME##__->tsd_key);   \
+    return erts_sspa_free(sspa_data_##NAME##__,				\
+			  id - 1,		                        \
+			  (char *) p);					\
+}
+
+
 #ifdef DEBUG
 #define ERTS_ALC_DBG_BLK_SZ(PTR) (*(((UWord *) (PTR)) - 2))
 #endif /* #ifdef DEBUG */
diff --git a/erts/emulator/beam/erl_alloc.types b/erts/emulator/beam/erl_alloc.types
index 11884299e2..bf5487d31e 100644
--- a/erts/emulator/beam/erl_alloc.types
+++ b/erts/emulator/beam/erl_alloc.types
@@ -351,11 +351,9 @@ type	SYS_CHECK_REQ	SHORT_LIVED	SYSTEM		system_check_request
 type  	TEMP_TERM 	TEMPORARY	SYSTEM		temp_term
 type	DRV_TAB		LONG_LIVED	SYSTEM		drv_tab
 type	DRV_EV_STATE	LONG_LIVED	SYSTEM		driver_event_state
-type	DRV_EV_D_STATE	FIXED_SIZE	SYSTEM		driver_event_data_state
 type	DRV_SEL_D_STATE	FIXED_SIZE	SYSTEM		driver_select_data_state
 type	NIF_SEL_D_STATE	FIXED_SIZE	SYSTEM		enif_select_data_state
 type	FD_LIST		SHORT_LIVED	SYSTEM		fd_list
-type	ACTIVE_FD_ARR	SHORT_LIVED	SYSTEM		active_fd_array
 type	POLLSET		LONG_LIVED	SYSTEM		pollset
 type	POLLSET_UPDREQ	SHORT_LIVED	SYSTEM		pollset_update_req
 type	POLL_FDS	LONG_LIVED	SYSTEM		poll_fds
diff --git a/erts/emulator/beam/erl_bif_info.c b/erts/emulator/beam/erl_bif_info.c
index 36939d6acc..17c936f041 100644
--- a/erts/emulator/beam/erl_bif_info.c
+++ b/erts/emulator/beam/erl_bif_info.c
@@ -46,6 +46,7 @@
 #include "erl_thr_progress.h"
 #include "erl_bif_unique.h"
 #include "erl_map.h"
+#include "erl_check_io.h"
 #define ERTS_PTAB_WANT_DEBUG_FUNCS__
 #include "erl_ptab.h"
 #include "erl_time.h"
@@ -97,9 +98,6 @@ static char erts_system_version[] = ("Erlang/OTP " ERLANG_OTP_RELEASE
 #ifdef HIPE
 				     " [hipe]"
 #endif	
-#ifdef ERTS_ENABLE_KERNEL_POLL
-				     " [kernel-poll:%s]"
-#endif	
 #ifdef ET_DEBUG
 #if ET_DEBUG
 				     " [type-assertions]"
@@ -371,9 +369,6 @@ erts_print_system_version(fmtfn_t to, void *arg, Process *c_p)
 		      , total, online
 		      , dirty_cpu, dirty_cpu_onln, dirty_io
 		      , erts_async_max_threads
-#ifdef ERTS_ENABLE_KERNEL_POLL
-		      , erts_use_kernel_poll ? "true" : "false"
-#endif
 	);
 }
 
@@ -2695,7 +2690,7 @@ BIF_RETTYPE system_info_1(BIF_ALIST_1)
 	BIF_RET(make_small(CONTEXT_REDS));
     } else if (ERTS_IS_ATOM_STR("kernel_poll", BIF_ARG_1)) {
 #ifdef ERTS_ENABLE_KERNEL_POLL
-	BIF_RET(erts_use_kernel_poll ? am_true : am_false);
+	BIF_RET(am_true);
 #else
 	BIF_RET(am_false);
 #endif    
@@ -2848,7 +2843,7 @@ BIF_RETTYPE system_info_1(BIF_ALIST_1)
 	BIF_RET(am_disabled);
     }
     else if (ERTS_IS_ATOM_STR("eager_check_io",BIF_ARG_1)) {
-	BIF_RET(erts_eager_check_io ? am_true : am_false);
+	BIF_RET(am_true);
     }
     else if (ERTS_IS_ATOM_STR("literal_test",BIF_ARG_1)) {
 #ifdef ERTS_HAVE_IS_IN_LITERAL_RANGE
@@ -3580,8 +3575,8 @@ BIF_RETTYPE erts_debug_get_internal_state_1(BIF_ALIST_1)
 						   (Uint) ciodi.no_used_fds),
 				     erts_bld_uint(hpp, szp,
 						   (Uint) ciodi.no_driver_select_structs),
-				     erts_bld_uint(hpp, szp,
-						   (Uint) ciodi.no_driver_event_structs));
+                                     erts_bld_uint(hpp, szp,
+                                                   (Uint) ciodi.no_enif_select_structs));
 		if (hpp)
 		    break;
 		hp = HAlloc(BIF_P, sz);
diff --git a/erts/emulator/beam/erl_driver.h b/erts/emulator/beam/erl_driver.h
index 5ad616fec3..d5379a40d5 100644
--- a/erts/emulator/beam/erl_driver.h
+++ b/erts/emulator/beam/erl_driver.h
@@ -148,14 +148,6 @@ typedef struct _erl_drv_event* ErlDrvEvent; /* An event to be selected on. */
 typedef struct _erl_drv_port* ErlDrvPort; /* A port descriptor. */
 typedef struct _erl_drv_port* ErlDrvThreadData; /* Thread data. */
 
-#if !defined(__WIN32__) && !defined(_WIN32) && !defined(_WIN32_) && !defined(USE_SELECT)
-struct erl_drv_event_data {
-    short events;
-    short revents;
-};
-#endif
-typedef struct erl_drv_event_data *ErlDrvEventData; /* Event data */
-
 typedef struct {
     unsigned long megasecs;
     unsigned long secs;
@@ -270,10 +262,7 @@ typedef struct erl_drv_entry {
 			 unsigned int *flags); /* Works mostly like 'control',
 						  a synchronous
 						  call into the driver. */
-    void (*event)(ErlDrvData drv_data, ErlDrvEvent event,
-		  ErlDrvEventData event_data);
-                                /* Called when an event selected by 
-				   driver_event() has occurred */
+    void (*unused_event_callback)(void);
     int extended_marker;	/* ERL_DRV_EXTENDED_MARKER */
     int major_version;		/* ERL_DRV_EXTENDED_MAJOR_VERSION */
     int minor_version;		/* ERL_DRV_EXTENDED_MINOR_VERSION */
@@ -340,8 +329,6 @@ EXTERN void erl_drv_busy_msgq_limits(ErlDrvPort port,
 				     ErlDrvSizeT *high);
 
 EXTERN int driver_select(ErlDrvPort port, ErlDrvEvent event, int mode, int on);
-EXTERN int driver_event(ErlDrvPort port, ErlDrvEvent event, 
-			ErlDrvEventData event_data);
 
 EXTERN int driver_output(ErlDrvPort port, char *buf, ErlDrvSizeT len);
 EXTERN int driver_output2(ErlDrvPort port, char *hbuf, ErlDrvSizeT hlen,
diff --git a/erts/emulator/beam/erl_init.c b/erts/emulator/beam/erl_init.c
index 8c14c86219..6cef9bd0e3 100644
--- a/erts/emulator/beam/erl_init.c
+++ b/erts/emulator/beam/erl_init.c
@@ -49,6 +49,7 @@
 #include "erl_bif_unique.h"
 #define ERTS_WANT_TIMER_WHEEL_API
 #include "erl_time.h"
+#include "erl_check_io.h"
 
 #ifdef HIPE
 #include "hipe_mode_switch.h"	/* for hipe_mode_switch_init() */
@@ -76,8 +77,10 @@ const char etp_otp_release[] = ERLANG_OTP_RELEASE;
 const char etp_compile_date[] = ERLANG_COMPILE_DATE;
 const char etp_arch[] = ERLANG_ARCHITECTURE;
 #ifdef ERTS_ENABLE_KERNEL_POLL
+const int erts_use_kernel_poll = 1;
 const int etp_kernel_poll_support = 1;
 #else
+const int erts_use_kernel_poll = 0;
 const int etp_kernel_poll_support = 0;
 #endif
 #if defined(ARCH_64)
@@ -203,16 +206,16 @@ int erts_no_line_info = 0;	/* -L: Don't load line information */
  */
 
 ErtsModifiedTimings erts_modified_timings[] = {
-    /* 0 */	{make_small(0), CONTEXT_REDS, INPUT_REDUCTIONS},
-    /* 1 */	{make_small(0), (3*CONTEXT_REDS)/4, 2*INPUT_REDUCTIONS},
-    /* 2 */	{make_small(0), CONTEXT_REDS/2, INPUT_REDUCTIONS/2},
-    /* 3 */	{make_small(0), (7*CONTEXT_REDS)/8, 3*INPUT_REDUCTIONS},
-    /* 4 */	{make_small(0), CONTEXT_REDS/3, 3*INPUT_REDUCTIONS},
-    /* 5 */	{make_small(0), (10*CONTEXT_REDS)/11, INPUT_REDUCTIONS/2},
-    /* 6 */	{make_small(1), CONTEXT_REDS/4, 2*INPUT_REDUCTIONS},
-    /* 7 */	{make_small(1), (5*CONTEXT_REDS)/7, INPUT_REDUCTIONS/3},
-    /* 8 */	{make_small(10), CONTEXT_REDS/5, 3*INPUT_REDUCTIONS},
-    /* 9 */	{make_small(10), (6*CONTEXT_REDS)/7, INPUT_REDUCTIONS/4}
+    /* 0 */	{make_small(0), CONTEXT_REDS},
+    /* 1 */	{make_small(0), (3*CONTEXT_REDS)/4},
+    /* 2 */	{make_small(0), CONTEXT_REDS/2},
+    /* 3 */	{make_small(0), (7*CONTEXT_REDS)/8},
+    /* 4 */	{make_small(0), CONTEXT_REDS/3},
+    /* 5 */	{make_small(0), (10*CONTEXT_REDS)/11},
+    /* 6 */	{make_small(1), CONTEXT_REDS/4},
+    /* 7 */	{make_small(1), (5*CONTEXT_REDS)/7},
+    /* 8 */	{make_small(10), CONTEXT_REDS/5},
+    /* 9 */	{make_small(10), (6*CONTEXT_REDS)/7}
 };
 
 #define ERTS_MODIFIED_TIMING_LEVELS \
@@ -310,8 +313,9 @@ erl_init(int ncpu,
     erts_init_sys_common_misc();
     erts_init_process(ncpu, proc_tab_sz, legacy_proc_tab);
     erts_init_scheduling(no_schedulers,
-			 no_schedulers_online
-			 , no_dirty_cpu_schedulers,
+			 no_schedulers_online,
+                         erts_no_poll_threads,
+			 no_dirty_cpu_schedulers,
 			 no_dirty_cpu_schedulers_online,
 			 no_dirty_io_schedulers
 			 );
@@ -558,9 +562,19 @@ void erts_usage(void)
     erts_fprintf(stderr, "-hmqd  val     set default message queue data flag for processes,\n");
     erts_fprintf(stderr, "               valid values are: off_heap | on_heap\n");
 
+    erts_fprintf(stderr, "-IOp number    set number of pollsets to be used to poll for I/O,\n");
+    erts_fprintf(stderr, "               This value has to be equal or smaller than the\n");
+    erts_fprintf(stderr, "               number of poll threads. If the current platform\n");
+    erts_fprintf(stderr, "               does not support concurrent update of pollsets\n");
+    erts_fprintf(stderr, "               this value is ignored.\n");
+    erts_fprintf(stderr, "-IOt number    set number of threads to be used to poll for I/O\n");
+    erts_fprintf(stderr, "-IOPp number   set number of pollsets as a percentage of the\n");
+    erts_fprintf(stderr, "               number of poll threads.");
+    erts_fprintf(stderr, "-IOPt number   set number of threads to be used to poll for I/O\n");
+    erts_fprintf(stderr, "               as a percentage of the number of schedulers.");
+
     /*    erts_fprintf(stderr, "-i module  set the boot module (default init)\n"); */
 
-    erts_fprintf(stderr, "-K boolean     enable or disable kernel poll\n");
     erts_fprintf(stderr, "-n[s|a|d]      Control behavior of signals to ports\n");
     erts_fprintf(stderr, "               Note that this flag is deprecated!\n");
     erts_fprintf(stderr, "-M<X> <Y>      memory allocator switches,\n");
@@ -727,7 +741,6 @@ early_init(int *argc, char **argv) /*
     char envbuf[21]; /* enough for any 64-bit integer */
     size_t envbufsz;
 
-
     erts_save_emu_args(*argc, argv);
 
     erts_sched_compact_load = 1;
@@ -839,6 +852,7 @@ early_init(int *argc, char **argv) /*
 		    }
 		    break;
 		}
+
 		case 'S' :
 		    if (argv[i][2] == 'P') {
 			int ptot, ponln;
@@ -1100,6 +1114,9 @@ early_init(int *argc, char **argv) /*
     erts_alloc_init(argc, argv, &alloc_opts); /* Handles (and removes)
 						 -M flags. */
     /* Require allocators */
+
+    erts_init_check_io(argc, argv);
+
     /*
      * Thread progress management:
      *
@@ -1107,13 +1124,14 @@ early_init(int *argc, char **argv) /*
      * ** Scheduler threads (see erl_process.c)
      * ** Aux thread (see erl_process.c)
      * ** Sys message dispatcher thread (see erl_trace.c)
+     * ** IO Poll threads (see erl_check_io.c)
      *
      * * Unmanaged threads that need to register:
      * ** Async threads (see erl_async.c)
      * ** Dirty scheduler threads
      */
     erts_thr_progress_init(no_schedulers,
-			   no_schedulers+2,
+			   no_schedulers+2+erts_no_poll_threads,
 			   erts_async_max_threads +
 			   erts_no_dirty_cpu_schedulers +
 			   erts_no_dirty_io_schedulers
@@ -1561,16 +1579,6 @@ erl_start(int argc, char **argv)
 	    have_break_handler = 0;
 	  break;
 
-	case 'K':
-	    /* If kernel poll support is present,
-	       erl_sys_args() will remove the K parameter
-	       and value */
-	    get_arg(argv[i]+2, argv[i+1], &i);
-	    erts_fprintf(stderr,
-		       "kernel-poll not supported; \"K\" parameter ignored\n",
-		       arg);
-	    break;
-
 	case 'n':
 	    arg = get_arg(argv[i]+2, argv[i+1], &i);
 	    switch (arg[0]) {
@@ -1740,22 +1748,9 @@ erl_start(int argc, char **argv)
 		    erts_usage();
 		}
 	    }
-	    else if (has_prefix("ecio", sub_param)) {
-		arg = get_arg(sub_param+4, argv[i+1], &i);
-#ifndef __OSE__
-		if (sys_strcmp("true", arg) == 0)
-		    erts_eager_check_io = 1;
-		else
-#endif
-		if (sys_strcmp("false", arg) == 0)
-		    erts_eager_check_io = 0;
-		else {
-		    erts_fprintf(stderr,
-				 "bad schedule eager check I/O value '%s'\n",
-				 arg);
-		    erts_usage();
-		}
-	    }
+            else if (has_prefix("ecio", sub_param)) {
+                /* ignore argument, eager check io no longer used */
+            }
 	    else if (has_prefix("pp", sub_param)) {
 		arg = get_arg(sub_param+2, argv[i+1], &i);
 		if (sys_strcmp(arg, "true") == 0)
diff --git a/erts/emulator/beam/erl_lock_check.c b/erts/emulator/beam/erl_lock_check.c
index f81c90818f..4cdef0200f 100644
--- a/erts/emulator/beam/erl_lock_check.c
+++ b/erts/emulator/beam/erl_lock_check.c
@@ -113,7 +113,6 @@ static erts_lc_lock_order_t erts_lock_order[] = {
     {	"drv_ev_state_grow",			NULL,   		},
     {	"drv_ev_state",				"address"		},
     {	"safe_hash",				"address"		},
-    {   "pollset_rm_list",                      NULL                    },
     {   "removed_fd_pre_alloc_lock",            "address"               },
     {   "state_prealloc",                       NULL                    },
     {	"schdlr_sspnd",				NULL			},
diff --git a/erts/emulator/beam/erl_lock_count.c b/erts/emulator/beam/erl_lock_count.c
index d2e8f47d59..1ae6076b12 100644
--- a/erts/emulator/beam/erl_lock_count.c
+++ b/erts/emulator/beam/erl_lock_count.c
@@ -554,16 +554,6 @@ erts_lock_flags_t erts_lcnt_get_category_mask() {
     return lcnt_category_mask__;
 }
 
-#ifdef ERTS_ENABLE_KERNEL_POLL
-/* erl_poll/erl_check_io only exports one of these variants at a time, and we
- * may need to use either one depending on emulator startup flags. */
-void erts_lcnt_update_pollset_locks_nkp(int);
-void erts_lcnt_update_pollset_locks_kp(int);
-
-void erts_lcnt_update_cio_locks_nkp(int);
-void erts_lcnt_update_cio_locks_kp(int);
-#endif
-
 void erts_lcnt_set_category_mask(erts_lock_flags_t mask) {
     erts_lock_flags_t changed_categories;
 
@@ -590,19 +580,7 @@ void erts_lcnt_set_category_mask(erts_lock_flags_t mask) {
     }
 
     if(changed_categories & ERTS_LOCK_FLAGS_CATEGORY_IO) {
-#ifdef ERTS_ENABLE_KERNEL_POLL
-        if(erts_use_kernel_poll) {
-            erts_lcnt_update_pollset_locks_kp(mask & ERTS_LOCK_FLAGS_CATEGORY_IO);
-            erts_lcnt_update_cio_locks_kp(mask & ERTS_LOCK_FLAGS_CATEGORY_IO);
-        } else {
-            erts_lcnt_update_pollset_locks_nkp(mask & ERTS_LOCK_FLAGS_CATEGORY_IO);
-            erts_lcnt_update_cio_locks_nkp(mask & ERTS_LOCK_FLAGS_CATEGORY_IO);
-        }
-#else
-        erts_lcnt_update_pollset_locks(mask & ERTS_LOCK_FLAGS_CATEGORY_IO);
         erts_lcnt_update_cio_locks(mask & ERTS_LOCK_FLAGS_CATEGORY_IO);
-#endif
-
         erts_lcnt_update_driver_locks(mask & ERTS_LOCK_FLAGS_CATEGORY_IO);
         erts_lcnt_update_port_locks(mask & ERTS_LOCK_FLAGS_CATEGORY_IO);
     }
diff --git a/erts/emulator/beam/erl_msacc.h b/erts/emulator/beam/erl_msacc.h
index 8349a7e297..2d4637f800 100644
--- a/erts/emulator/beam/erl_msacc.h
+++ b/erts/emulator/beam/erl_msacc.h
@@ -318,8 +318,8 @@ ERTS_GLB_INLINE
 void erts_msacc_set_state_um__(ErtsMsAcc *msacc, Uint new_state, int increment) {
     if (ERTS_UNLIKELY(msacc->unmanaged)) {
         erts_mtx_lock(&msacc->mtx);
-        msacc->state = new_state;
         if (ERTS_LIKELY(!msacc->perf_counter)) {
+            msacc->state = new_state;
             erts_mtx_unlock(&msacc->mtx);
             return;
         }
diff --git a/erts/emulator/beam/erl_port_task.c b/erts/emulator/beam/erl_port_task.c
index 14977dfa17..a588477320 100644
--- a/erts/emulator/beam/erl_port_task.c
+++ b/erts/emulator/beam/erl_port_task.c
@@ -36,6 +36,7 @@
 #include "erl_check_io.h"
 #include "dtrace-wrapper.h"
 #include "lttng-wrapper.h"
+#include "erl_check_io.h"
 #include <stdarg.h>
 
 /*
@@ -90,8 +91,6 @@ static void chk_task_queues(Port *pp, ErtsPortTask *execq, int processing_busy_q
 				    erts_atomic_read_nob(&(PP)->run_queue))); \
     } while (0)
 
-erts_atomic_t erts_port_task_outstanding_io_tasks;
-
 #define ERTS_PT_STATE_SCHEDULED		0
 #define ERTS_PT_STATE_ABORTED		1
 #define ERTS_PT_STATE_EXECUTING		2
@@ -99,7 +98,6 @@ erts_atomic_t erts_port_task_outstanding_io_tasks;
 typedef union {
     struct { /* I/O tasks */
 	ErlDrvEvent event;
-	ErlDrvEventData event_data;
     } io;
     struct {
 	ErtsProc2PortSigCallback callback;
@@ -149,10 +147,10 @@ static void begin_port_cleanup(Port *pp,
 			       ErtsPortTask **execq,
 			       int *processing_busy_q_p);
 
-ERTS_SCHED_PREF_QUICK_ALLOC_IMPL(port_task,
-				 ErtsPortTask,
-				 1000,
-				 ERTS_ALC_T_PORT_TASK)
+ERTS_THR_PREF_QUICK_ALLOC_IMPL(port_task,
+                               ErtsPortTask,
+                               1000,
+                               ERTS_ALC_T_PORT_TASK)
 
 ERTS_SCHED_PREF_QUICK_ALLOC_IMPL(busy_caller_table,
 				 ErtsPortTaskBusyCallerTable,
@@ -585,8 +583,9 @@ reset_executed_io_task_handle(ErtsPortTask *ptp)
 {
     if (ptp->u.alive.handle) {
 	ASSERT(ptp == handle2task(ptp->u.alive.handle));
-	erts_io_notify_port_task_executed(ptp->u.alive.handle);
-	reset_port_task_handle(ptp->u.alive.handle);
+        /* The port task handle is reset inside task_executed */
+	erts_io_notify_port_task_executed(ptp->type, ptp->u.alive.handle,
+                                          reset_port_task_handle);
     }
 }
 
@@ -1308,21 +1307,7 @@ erts_port_task_abort(ErtsPortTaskHandle *pthp)
 	if (old_state != ERTS_PT_STATE_SCHEDULED)
 	    res = - 1; /* Task already aborted, executing, or executed */
 	else {
-
 	    reset_port_task_handle(pthp);
-
-	    switch (ptp->type) {
-	    case ERTS_PORT_TASK_INPUT:
-	    case ERTS_PORT_TASK_OUTPUT:
-	    case ERTS_PORT_TASK_EVENT:
-		ASSERT(erts_atomic_read_nob(
-			   &erts_port_task_outstanding_io_tasks) > 0);
-		erts_atomic_dec_relb(&erts_port_task_outstanding_io_tasks);
-		break;
-	    default:
-		break;
-	    }
-
 	    res = 0;
 	}
     }
@@ -1459,16 +1444,6 @@ erts_port_task_schedule(Eterm id,
 	va_start(argp, type);
 	ptp->u.alive.td.io.event = va_arg(argp, ErlDrvEvent);
 	va_end(argp);
-	erts_atomic_inc_relb(&erts_port_task_outstanding_io_tasks);
-	break;
-    }
-    case ERTS_PORT_TASK_EVENT: {
-	va_list argp;
-	va_start(argp, type);
-	ptp->u.alive.td.io.event = va_arg(argp, ErlDrvEvent);
-	ptp->u.alive.td.io.event_data = va_arg(argp, ErlDrvEventData);
-	va_end(argp);
-	erts_atomic_inc_relb(&erts_port_task_outstanding_io_tasks);
 	break;
     }
     case ERTS_PORT_TASK_PROC_SIG: {
@@ -1644,13 +1619,12 @@ erts_port_task_free_port(Port *pp)
  * scheduling of processes. Run-queue lock should be held by caller.
  */
 
-int
+void
 erts_port_task_execute(ErtsRunQueue *runq, Port **curr_port_pp)
 {
     Port *pp;
     ErtsPortTask *execq;
     int processing_busy_q;
-    int res = 0;
     int vreds = 0;
     int reds = 0;
     erts_aint_t io_tasks_executed = 0;
@@ -1665,7 +1639,6 @@ erts_port_task_execute(ErtsRunQueue *runq, Port **curr_port_pp)
 
     pp = pop_port(runq);
     if (!pp) {
-	res = 0;
 	goto done;
     }
 
@@ -1768,17 +1741,6 @@ erts_port_task_execute(ErtsRunQueue *runq, Port **curr_port_pp)
 	    reset_executed_io_task_handle(ptp);
 	    io_tasks_executed++;
 	    break;
-	case ERTS_PORT_TASK_EVENT:
-	    reds = ERTS_PORT_REDS_EVENT;
-	    ASSERT((state & ERTS_PORT_SFLGS_DEAD) == 0);
-            DTRACE_DRIVER(driver_event, pp);
-            LTTNG_DRIVER(driver_event, pp);
-	    (*pp->drv_ptr->event)((ErlDrvData) pp->drv_data,
-				  ptp->u.alive.td.io.event,
-				  ptp->u.alive.td.io.event_data);
-	    reset_executed_io_task_handle(ptp);
-	    io_tasks_executed++;
-	    break;
 	case ERTS_PORT_TASK_PROC_SIG: {
 	    ErtsProc2PortSigData *sigdp = &ptp->u.alive.td.psig.data;
 	    reset_handle(ptp);
@@ -1843,14 +1805,6 @@ erts_port_task_execute(ErtsRunQueue *runq, Port **curr_port_pp)
     erts_unblock_fpe(fpe_was_unmasked);
     ERTS_MSACC_POP_STATE_M();
 
-
-    if (io_tasks_executed) {
-	ASSERT(erts_atomic_read_nob(&erts_port_task_outstanding_io_tasks)
-	       >= io_tasks_executed);
-	erts_atomic_add_relb(&erts_port_task_outstanding_io_tasks,
-				 -1*io_tasks_executed);
-    }
-
     ASSERT(runq == (ErtsRunQueue *) erts_atomic_read_nob(&pp->run_queue));
 
     active = finalize_exec(pp, &execq, processing_busy_q);
@@ -1891,15 +1845,11 @@ erts_port_task_execute(ErtsRunQueue *runq, Port **curr_port_pp)
     }
 
  done:
-    res = (erts_atomic_read_nob(&erts_port_task_outstanding_io_tasks)
-	   != (erts_aint_t) 0);
 
     runq->scheduler->reductions += reds;
 
     ERTS_LC_ASSERT(erts_lc_runq_is_locked(runq));
     ERTS_PORT_REDUCTIONS_EXECUTED(esdp, runq, reds);
-
-    return res;
 }
 
 static void
@@ -2031,13 +1981,6 @@ begin_port_cleanup(Port *pp, ErtsPortTask **execqp, int *processing_busy_q_p)
 				      DO_WRITE,
 				      1);
 		break;
-	    case ERTS_PORT_TASK_EVENT:
-		erts_stale_drv_select(pp->common.id,
-				      ERTS_Port2ErlDrvPort(pp),
-				      ptp->u.alive.td.io.event,
-				      0,
-				      1);
-		break;
 	    case ERTS_PORT_TASK_DIST_CMD:
 		break;
 	    case ERTS_PORT_TASK_PROC_SIG: {
@@ -2151,8 +2094,7 @@ erts_dequeue_port(ErtsRunQueue *rq)
 void
 erts_port_task_init(void)
 {
-    erts_atomic_init_nob(&erts_port_task_outstanding_io_tasks,
-			     (erts_aint_t) 0);
-    init_port_task_alloc();
+    init_port_task_alloc(erts_no_schedulers + erts_no_poll_threads
+                         + 1); /* aux_thread */
     init_busy_caller_table_alloc();
 }
diff --git a/erts/emulator/beam/erl_port_task.h b/erts/emulator/beam/erl_port_task.h
index 561f4ca936..ae78a7d8a3 100644
--- a/erts/emulator/beam/erl_port_task.h
+++ b/erts/emulator/beam/erl_port_task.h
@@ -56,17 +56,11 @@ typedef erts_atomic_t ErtsPortTaskHandle;
 typedef enum {
     ERTS_PORT_TASK_INPUT,
     ERTS_PORT_TASK_OUTPUT,
-    ERTS_PORT_TASK_EVENT,
     ERTS_PORT_TASK_TIMEOUT,
     ERTS_PORT_TASK_DIST_CMD,
     ERTS_PORT_TASK_PROC_SIG
 } ErtsPortTaskType;
 
-#ifdef ERTS_INCLUDE_SCHEDULER_INTERNALS
-/* NOTE: Do not access any of the exported variables directly */
-extern erts_atomic_t erts_port_task_outstanding_io_tasks;
-#endif
-
 #define ERTS_PTS_FLG_IN_RUNQ			(((erts_aint32_t) 1) <<  0)
 #define ERTS_PTS_FLG_EXEC			(((erts_aint32_t) 1) <<  1)
 #define ERTS_PTS_FLG_HAVE_TASKS			(((erts_aint32_t) 1) <<  2)
@@ -140,10 +134,6 @@ ERTS_GLB_INLINE void erts_port_task_sched_unlock(ErtsPortTaskSched *ptsp);
 ERTS_GLB_INLINE int erts_port_task_sched_lock_is_locked(ErtsPortTaskSched *ptsp);
 ERTS_GLB_INLINE void erts_port_task_sched_enter_exiting_state(ErtsPortTaskSched *ptsp);
 
-#ifdef ERTS_INCLUDE_SCHEDULER_INTERNALS
-ERTS_GLB_INLINE int erts_port_task_have_outstanding_io_tasks(void);
-#endif
-
 #if ERTS_GLB_INLINE_INCL_FUNC_DEF
 
 ERTS_GLB_INLINE void
@@ -221,24 +211,16 @@ erts_port_task_sched_enter_exiting_state(ErtsPortTaskSched *ptsp)
     erts_atomic32_read_bor_nob(&ptsp->flags, ERTS_PTS_FLG_EXITING);
 }
 
-#ifdef ERTS_INCLUDE_SCHEDULER_INTERNALS
-
-ERTS_GLB_INLINE int
-erts_port_task_have_outstanding_io_tasks(void)
-{
-    return (erts_atomic_read_acqb(&erts_port_task_outstanding_io_tasks)
-	    != 0);
-}
-
-#endif /* ERTS_INCLUDE_SCHEDULER_INTERNALS */
-
 #endif
 
 #ifdef ERTS_INCLUDE_SCHEDULER_INTERNALS
-int erts_port_task_execute(ErtsRunQueue *, Port **);
+void erts_port_task_execute(ErtsRunQueue *, Port **);
 void erts_port_task_init(void);
 #endif
 
+/* generated for 'port_task' quick allocator */
+void erts_port_task_pre_alloc_init_thread(void);
+
 void erts_port_task_tmp_handle_detach(ErtsPortTaskHandle *);
 int erts_port_task_abort(ErtsPortTaskHandle *);
 
diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index f3f99f1835..61fdf86a56 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -24,6 +24,8 @@
 #  include "config.h"
 #endif
 
+#define ERTS_WANT_BREAK_HANDLING
+
 #include <stddef.h> /* offsetof() */
 #include "sys.h"
 #include "erl_vm.h"
@@ -49,6 +51,8 @@
 #define ERTS_WANT_TIMER_WHEEL_API
 #include "erl_time.h"
 #include "erl_nfunc_sched.h"
+#include "erl_check_io.h"
+#include "erl_poll.h"
 
 #define ERTS_CHECK_TIME_REDS CONTEXT_REDS
 #define ERTS_DELAYED_WAKEUP_INFINITY (~(Uint64) 0)
@@ -170,7 +174,6 @@ extern BeamInstr beam_exit[];
 extern BeamInstr beam_continue_exit[];
 
 int ERTS_WRITE_UNLIKELY(erts_default_spo_flags) = SPO_ON_HEAP_MSGQ;
-int ERTS_WRITE_UNLIKELY(erts_eager_check_io) = 1;
 int ERTS_WRITE_UNLIKELY(erts_sched_compact_load);
 int ERTS_WRITE_UNLIKELY(erts_sched_balance_util) = 0;
 Uint ERTS_WRITE_UNLIKELY(erts_no_schedulers);
@@ -198,7 +201,7 @@ int erts_dio_sched_thread_suggested_stack_size = -1;
 ErtsLcPSDLocks erts_psd_required_locks[ERTS_PSD_SIZE];
 #endif
 
-static struct {
+static struct ErtsSchedBusyWait_ {
     int aux_work;
     int tse;
     int sys_schedule;
@@ -207,25 +210,26 @@ static struct {
 int erts_disable_proc_not_running_opt;
 
 static ErtsAuxWorkData *aux_thread_aux_work_data;
+static ErtsAuxWorkData *poll_thread_aux_work_data;
 
 #define ERTS_SCHDLR_SSPND_CHNG_NMSB		(((erts_aint32_t) 1) << 0)
 #define ERTS_SCHDLR_SSPND_CHNG_MSB		(((erts_aint32_t) 1) << 1)
 #define ERTS_SCHDLR_SSPND_CHNG_ONLN		(((erts_aint32_t) 1) << 2)
 #define ERTS_SCHDLR_SSPND_CHNG_DCPU_ONLN	(((erts_aint32_t) 1) << 3)
 
-typedef struct {
+typedef struct ErtsMultiSchedulingBlock_ {
     int ongoing;
     ErtsProcList *blckrs;
     ErtsProcList *chngq;
 } ErtsMultiSchedulingBlock;
 
-typedef struct {
+typedef struct ErtsSchedTypeCounters_ {
     Uint32 normal;
     Uint32 dirty_cpu;
     Uint32 dirty_io;
 } ErtsSchedTypeCounters;
 
-static struct {
+static struct ErtsSchedSuspend_ {
     erts_mtx_t mtx;
     ErtsSchedTypeCounters online;
     ErtsSchedTypeCounters curr_online;
@@ -364,9 +368,6 @@ erts_sched_stat_t erts_sched_stat;
 
 static erts_tsd_key_t ERTS_WRITE_UNLIKELY(sched_data_key);
 
-static erts_atomic32_t function_calls;
-
-static erts_atomic32_t doing_sys_schedule;
 static erts_atomic32_t no_empty_run_queues;
 long erts_runq_supervision_interval = 0;
 static ethr_event runq_supervision_event;
@@ -434,6 +435,7 @@ typedef union {
 static ErtsAlignedSchedulerSleepInfo *aligned_sched_sleep_info;
 static ErtsAlignedSchedulerSleepInfo *aligned_dirty_cpu_sched_sleep_info;
 static ErtsAlignedSchedulerSleepInfo *aligned_dirty_io_sched_sleep_info;
+static ErtsAlignedSchedulerSleepInfo *aligned_poll_thread_sleep_info;
 
 static Uint last_reductions;
 static Uint last_exact_reductions;
@@ -501,9 +503,13 @@ ERTS_SCHED_PREF_QUICK_ALLOC_IMPL(proclist,
 				 200,
 				 ERTS_ALC_T_PROC_LIST)
 
+#define ERTS_POLL_THREAD_SLEEP_INFO_IX(IX)                              \
+        (ASSERT(0 <= ((int) (IX))                                       \
+                && ((int) (IX)) < ((int) erts_no_poll_threads)),        \
+         &aligned_poll_thread_sleep_info[(IX)].ssi)
 #define ERTS_SCHED_SLEEP_INFO_IX(IX)					\
-    (ASSERT(-1 <= ((int) (IX))					        \
-		 && ((int) (IX)) < ((int) erts_no_schedulers)),		\
+    (ASSERT(((int)-1) <= ((int) (IX))                 \
+            && ((int) (IX)) < ((int) erts_no_schedulers)),		\
      &aligned_sched_sleep_info[(IX)].ssi)
 #define ERTS_DIRTY_CPU_SCHED_SLEEP_INFO_IX(IX)				\
     (ASSERT(0 <= ((int) (IX))					        \
@@ -1135,13 +1141,11 @@ dirty_sched_wall_time_change(ErtsSchedulerData *esdp, int working)
     mod++;
     erts_atomic32_set_nob(&esdp->sched_wall_time.u.mod, mod);
 
-#if 0
     if (!working) {
-        ERTS_MSACC_SET_STATE_M_X(ERTS_MSACC_STATE_BUSY_WAIT);
+        ERTS_MSACC_SET_STATE_X(ERTS_MSACC_STATE_BUSY_WAIT);
     } else {
-        ERTS_MSACC_SET_STATE_M_X(ERTS_MSACC_STATE_OTHER);
+        ERTS_MSACC_SET_STATE_X(ERTS_MSACC_STATE_OTHER);
     }
-#endif
 }
 
 
@@ -1559,18 +1563,19 @@ erts_psd_set_init(Process *p, int ix, void *data)
 
 
 void
-erts_sched_finish_poke(ErtsSchedulerSleepInfo *ssi, erts_aint32_t flags)
+erts_sched_finish_poke(ErtsSchedulerSleepInfo *ssi,
+                       erts_aint32_t flags)
 {
     switch (flags & ERTS_SSI_FLGS_SLEEP_TYPE) {
     case ERTS_SSI_FLG_POLL_SLEEPING:
-	erts_sys_schedule_interrupt(1);
+	erts_check_io_interrupt(ssi->psi, 1);
 	break;
     case ERTS_SSI_FLG_POLL_SLEEPING|ERTS_SSI_FLG_TSE_SLEEPING:
 	/*
 	 * Thread progress blocking while poll sleeping; need
 	 * to signal on both...
 	 */
-	erts_sys_schedule_interrupt(1);
+	erts_check_io_interrupt(ssi->psi, 1);
 	/* fall through */
     case ERTS_SSI_FLG_TSE_SLEEPING:
 	erts_tse_set(ssi->event);
@@ -2830,36 +2835,6 @@ erts_set_aux_work_timeout(int ix, erts_aint32_t type, int enable)
     return old;
 }
 
-
-
-static ERTS_INLINE void
-sched_waiting_sys(Uint no, ErtsRunQueue *rq)
-{
-    ERTS_LC_ASSERT(erts_lc_runq_is_locked(rq));
-    ASSERT(rq->waiting >= 0);
-    (void) ERTS_RUNQ_FLGS_SET(rq, (ERTS_RUNQ_FLG_OUT_OF_WORK
-				   | ERTS_RUNQ_FLG_HALFTIME_OUT_OF_WORK));
-    rq->waiting++;
-    rq->waiting *= -1;
-    rq->woken = 0;
-    if (erts_system_profile_flags.scheduler)
-	profile_scheduler(make_small(no), am_inactive);
-}
-
-static ERTS_INLINE void
-sched_active_sys(Uint no, ErtsRunQueue *rq)
-{
-    ERTS_LC_ASSERT(erts_lc_runq_is_locked(rq));
-
-    ASSERT(!ERTS_RUNQ_IX_IS_DIRTY(rq->ix));
-
-    ASSERT(rq->waiting < 0);
-    rq->waiting *= -1;
-    rq->waiting--;
-    if (erts_system_profile_flags.scheduler)
-	profile_scheduler(make_small(no), am_active);
-}
-
 Uint
 erts_active_schedulers(void)
 {
@@ -2870,49 +2845,6 @@ erts_active_schedulers(void)
     return as;
 }
 
-
-static ERTS_INLINE void
-clear_sys_scheduling(void)
-{
-    erts_atomic32_set_mb(&doing_sys_schedule, 0);
-}
-
-static ERTS_INLINE int
-try_set_sys_scheduling(void)
-{
-    return 0 == erts_atomic32_cmpxchg_acqb(&doing_sys_schedule, 1, 0);
-}
-
-
-static ERTS_INLINE int
-prepare_for_sys_schedule(int non_blocking)
-{
-    if (non_blocking && erts_eager_check_io) {
-	return try_set_sys_scheduling();
-    }
-    else {
-	while (!erts_port_task_have_outstanding_io_tasks()
-	       && try_set_sys_scheduling()) {
-	    if (!erts_port_task_have_outstanding_io_tasks())
-		return 1;
-	    clear_sys_scheduling();
-	}
-	return 0;
-    }
-}
-
-
-static ERTS_INLINE void
-sched_change_waiting_sys_to_waiting(Uint no, ErtsRunQueue *rq)
-{
-    ERTS_LC_ASSERT(erts_lc_runq_is_locked(rq));
-
-    ASSERT(!ERTS_RUNQ_IX_IS_DIRTY(rq->ix));
-
-    ASSERT(rq->waiting < 0);
-    rq->waiting *= -1;
-}
-
 static ERTS_INLINE void
 sched_waiting(Uint no, ErtsRunQueue *rq)
 {
@@ -3084,7 +3016,7 @@ sched_set_sleeptype(ErtsSchedulerSleepInfo *ssi, erts_aint32_t sleep_type)
 	erts_tse_reset(ssi->event);
     else {
 	ASSERT(sleep_type == ERTS_SSI_FLG_POLL_SLEEPING);
-	erts_sys_schedule_interrupt(0);
+        erts_check_io_interrupt(ssi->psi, 0);
     }
 
     while (1) {
@@ -3152,6 +3084,12 @@ thr_prgr_fin_wait(void *vssi)
 
 static void init_aux_work_data(ErtsAuxWorkData *awdp, ErtsSchedulerData *esdp, char *dawwp);
 
+void
+erts_aux_thread_poke()
+{
+    erts_sched_poke(ERTS_SCHED_SLEEP_INFO_IX(-1));
+}
+
 static void *
 aux_thread(void *unused)
 {
@@ -3160,6 +3098,7 @@ aux_thread(void *unused)
     erts_aint32_t aux_work;
     ErtsThrPrgrCallbacks callbacks;
     int thr_prgr_active = 1;
+    ERTS_MSACC_DECLARE_CACHE();
 
 #ifdef ERTS_ENABLE_LOCK_CHECK
     {
@@ -3168,6 +3107,7 @@ aux_thread(void *unused)
     }
 #endif
 
+    erts_port_task_pre_alloc_init_thread();
     ssi->event = erts_tse_fetch();
 
     erts_msacc_init_thread("aux", 1, 1);
@@ -3182,9 +3122,14 @@ aux_thread(void *unused)
     init_aux_work_data(awdp, NULL, NULL);
     awdp->ssi = ssi;
 
+#if ERTS_POLL_USE_FALLBACK
+    ssi->psi = erts_create_pollset_thread(-1);
+#endif
 
     sched_prep_spin_wait(ssi);
 
+    ERTS_MSACC_SET_STATE_CACHED(ERTS_MSACC_STATE_OTHER);
+
     while (1) {
 	erts_aint32_t flgs;
 
@@ -3193,30 +3138,54 @@ aux_thread(void *unused)
 	    if (!thr_prgr_active)
 		erts_thr_progress_active(NULL, thr_prgr_active = 1);
 	    aux_work = handle_aux_work(awdp, aux_work, 1);
+            ERTS_MSACC_UPDATE_CACHE();
 	    if (aux_work && erts_thr_progress_update(NULL))
 		erts_thr_progress_leader_update(NULL);
 	}
 
 	if (!aux_work) {
+
+#ifdef ERTS_BREAK_REQUESTED
+            if (ERTS_BREAK_REQUESTED)
+                erts_do_break_handling();
+#endif
+
 	    if (thr_prgr_active)
 		erts_thr_progress_active(NULL, thr_prgr_active = 0);
-	    erts_thr_progress_prepare_wait(NULL);
+
+#if ERTS_POLL_USE_FALLBACK
 
 	    flgs = sched_spin_wait(ssi, 0);
 
 	    if (flgs & ERTS_SSI_FLG_SLEEPING) {
 		ASSERT(flgs & ERTS_SSI_FLG_WAITING);
+		flgs = sched_set_sleeptype(ssi, ERTS_SSI_FLG_POLL_SLEEPING);
+		if (flgs & ERTS_SSI_FLG_SLEEPING) {
+		    ASSERT(flgs & ERTS_SSI_FLG_POLL_SLEEPING);
+		    ASSERT(flgs & ERTS_SSI_FLG_WAITING);
+                    erts_check_io(ssi->psi);
+		}
+            }
+#else
+            erts_thr_progress_prepare_wait(NULL);
+
+	    flgs = sched_spin_wait(ssi, 0);
+
+	    if (flgs & ERTS_SSI_FLG_SLEEPING) {
 		flgs = sched_set_sleeptype(ssi, ERTS_SSI_FLG_TSE_SLEEPING);
 		if (flgs & ERTS_SSI_FLG_SLEEPING) {
-		    int res;
+                    int res;
 		    ASSERT(flgs & ERTS_SSI_FLG_TSE_SLEEPING);
 		    ASSERT(flgs & ERTS_SSI_FLG_WAITING);
-		    do {
-			res = erts_tse_wait(ssi->event);
-		    } while (res == EINTR);
+                    ERTS_MSACC_SET_STATE_CACHED(ERTS_MSACC_STATE_SLEEP);
+                    do {
+                        res = erts_tse_wait(ssi->event);
+                    } while (res == EINTR);
+                    ERTS_MSACC_SET_STATE_CACHED(ERTS_MSACC_STATE_OTHER);
 		}
-	    }
-	    erts_thr_progress_finalize_wait(NULL);
+            }
+            erts_thr_progress_finalize_wait(NULL);
+#endif
 	}
 
 	flgs = sched_prep_spin_wait(ssi);
@@ -3224,8 +3193,79 @@ aux_thread(void *unused)
     return NULL;
 }
 
-static void suspend_scheduler(ErtsSchedulerData *esdp);
+static void *
+poll_thread(void *arg)
+{
+    int id = (int)(UWord)arg;
+    ErtsAuxWorkData *awdp = poll_thread_aux_work_data+id;
+    ErtsSchedulerSleepInfo *ssi = ERTS_POLL_THREAD_SLEEP_INFO_IX(id);
+    erts_aint32_t aux_work;
+    ErtsThrPrgrCallbacks callbacks;
+    int thr_prgr_active = 1;
+    struct erts_poll_thread *psi = erts_create_pollset_thread(id);
+    ERTS_MSACC_DECLARE_CACHE();
+
+#ifdef ERTS_ENABLE_LOCK_CHECK
+    {
+	char buf[] = "poll_thread";
+	erts_lc_set_thread_name(buf);
+    }
+#endif
+
+    erts_port_task_pre_alloc_init_thread();
+    ssi->event = erts_tse_fetch();
+
+    erts_msacc_init_thread("poll", id, 0);
+
+    callbacks.arg = (void *) ssi;
+    callbacks.wakeup = thr_prgr_wakeup;
+    callbacks.prepare_wait = thr_prgr_prep_wait;
+    callbacks.wait = thr_prgr_wait;
+    callbacks.finalize_wait = thr_prgr_fin_wait;
+
+    erts_thr_progress_register_managed_thread(NULL, &callbacks, 0);
+    init_aux_work_data(awdp, NULL, NULL);
+    awdp->ssi = ssi;
+    ssi->psi = psi;
+
+    sched_prep_spin_wait(ssi);
+
+    ERTS_MSACC_SET_STATE_CACHED(ERTS_MSACC_STATE_OTHER);
 
+    while (1) {
+	erts_aint32_t flgs;
+
+	aux_work = erts_atomic32_read_acqb(&ssi->aux_work);
+	if (aux_work) {
+	    if (!thr_prgr_active)
+		erts_thr_progress_active(NULL, thr_prgr_active = 1);
+	    aux_work = handle_aux_work(awdp, aux_work, 1);
+            ERTS_MSACC_UPDATE_CACHE();
+	    if (aux_work && erts_thr_progress_update(NULL))
+		erts_thr_progress_leader_update(NULL);
+	}
+
+	if (!aux_work) {
+	    if (thr_prgr_active)
+		erts_thr_progress_active(NULL, thr_prgr_active = 0);
+
+	    flgs = sched_spin_wait(ssi, 0);
+
+	    if (flgs & ERTS_SSI_FLG_SLEEPING) {
+		ASSERT(flgs & ERTS_SSI_FLG_WAITING);
+		flgs = sched_set_sleeptype(ssi, ERTS_SSI_FLG_POLL_SLEEPING);
+		if (flgs & ERTS_SSI_FLG_SLEEPING) {
+		    ASSERT(flgs & ERTS_SSI_FLG_POLL_SLEEPING);
+		    ASSERT(flgs & ERTS_SSI_FLG_WAITING);
+                    erts_check_io(psi);
+		}
+	    }
+	}
+
+	flgs = sched_prep_spin_wait(ssi);
+    }
+    return NULL;
+}
 
 static void
 scheduler_wait(int *fcalls, ErtsSchedulerData *esdp, ErtsRunQueue *rq)
@@ -3260,318 +3300,136 @@ scheduler_wait(int *fcalls, ErtsSchedulerData *esdp, ErtsRunQueue *rq)
         dirty_active(esdp, -1);
     }
 
-    /*
-     * If all schedulers are waiting, one of them *should*
-     * be waiting in erl_sys_schedule()
-     */
-
-    if (ERTS_SCHEDULER_IS_DIRTY(esdp) || !prepare_for_sys_schedule(0)) {
-
-	sched_waiting(esdp->no, rq);
-
-	erts_runq_unlock(rq);
-
-	spincount = sched_busy_wait.tse;
+    sched_waiting(esdp->no, rq);
 
-    tse_wait:
-
-	if (ERTS_SCHEDULER_IS_DIRTY(esdp))
-	    dirty_sched_wall_time_change(esdp, working = 0);
-        else if (thr_prgr_active != working)
-	    sched_wall_time_change(esdp, working = thr_prgr_active);
-
-	while (1) {
-	    ErtsMonotonicTime current_time = 0;
+    erts_runq_unlock(rq);
 
-	    aux_work = erts_atomic32_read_acqb(&ssi->aux_work);
-	    if (aux_work && !ERTS_SCHEDULER_IS_DIRTY(esdp)) {
-		if (!thr_prgr_active) {
-		    erts_thr_progress_active(esdp, thr_prgr_active = 1);
-		    sched_wall_time_change(esdp, 1);
-		}
-		aux_work = handle_aux_work(&esdp->aux_work_data, aux_work, 1);
-                ERTS_MSACC_UPDATE_CACHE();
-		if (aux_work && erts_thr_progress_update(esdp))
-		    erts_thr_progress_leader_update(esdp);
-	    }
+    spincount = sched_busy_wait.tse;
 
-	    if (aux_work) {
-		if (!ERTS_SCHEDULER_IS_DIRTY(esdp)) {
-		    flgs = erts_atomic32_read_acqb(&ssi->flags);
-		    current_time = erts_get_monotonic_time(esdp);
-		    if (current_time >= erts_next_timeout_time(esdp->next_tmo_ref)) {
-			if (!thr_prgr_active) {
-			    erts_thr_progress_active(esdp, thr_prgr_active = 1);
-			    sched_wall_time_change(esdp, 1);
-			}
-			erts_bump_timers(esdp->timer_wheel, current_time);
-		    }
-		}
-	    }
-	    else {
-		ErtsMonotonicTime timeout_time;
-		int do_timeout = 0;
-		if (!ERTS_SCHEDULER_IS_DIRTY(esdp)) {
-		    timeout_time = erts_check_next_timeout_time(esdp);
-		    current_time = erts_get_monotonic_time(esdp);
-		    do_timeout = (current_time >= timeout_time);
-		} else {
-		    current_time = 0;
-		    timeout_time = ERTS_MONOTONIC_TIME_MAX;
-		}
-		if (do_timeout) {
-		    if (!thr_prgr_active) {
-			erts_thr_progress_active(esdp, thr_prgr_active = 1);
-			sched_wall_time_change(esdp, 1);
-		    }
-		}
-		else {
-		    if (!ERTS_SCHEDULER_IS_DIRTY(esdp)) {
-			if (thr_prgr_active) {
-			    erts_thr_progress_active(esdp, thr_prgr_active = 0);
-			    sched_wall_time_change(esdp, 0);
-			}
-			erts_thr_progress_prepare_wait(esdp);
-		    }
+    if (ERTS_SCHEDULER_IS_DIRTY(esdp))
+        dirty_sched_wall_time_change(esdp, working = 0);
+    else if (thr_prgr_active != working)
+        sched_wall_time_change(esdp, working = thr_prgr_active);
 
-		    flgs = sched_spin_wait(ssi, spincount);
-		    if (flgs & ERTS_SSI_FLG_SLEEPING) {
-			ASSERT(flgs & ERTS_SSI_FLG_WAITING);
-			flgs = sched_set_sleeptype(ssi, ERTS_SSI_FLG_TSE_SLEEPING);
-			if (flgs & ERTS_SSI_FLG_SLEEPING) {
-			    int res;
-			    ASSERT(flgs & ERTS_SSI_FLG_TSE_SLEEPING);
-			    ASSERT(flgs & ERTS_SSI_FLG_WAITING);
-			    current_time = ERTS_SCHEDULER_IS_DIRTY(esdp) ? 0 :
-				erts_get_monotonic_time(esdp);
-			    do {
-				Sint64 timeout;
-				if (current_time >= timeout_time)
-				    break;
-				if (!ERTS_SCHEDULER_IS_DIRTY(esdp)) {
-				    timeout = ERTS_MONOTONIC_TO_NSEC(timeout_time
-								     - current_time
-								     - 1) + 1;
-				} else
-				    timeout = -1;
-                                ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_SLEEP);
-				res = erts_tse_twait(ssi->event, timeout);
-                                ERTS_MSACC_POP_STATE_M();
-				current_time = ERTS_SCHEDULER_IS_DIRTY(esdp) ? 0 :
-				    erts_get_monotonic_time(esdp);
-			    } while (res == EINTR);
-			}
-		    }
-		    if (!ERTS_SCHEDULER_IS_DIRTY(esdp))
-			erts_thr_progress_finalize_wait(esdp);
-		}
-		if (!ERTS_SCHEDULER_IS_DIRTY(esdp) && current_time >= timeout_time)
-		    erts_bump_timers(esdp->timer_wheel, current_time);
-	    }
+    while (1) {
+        ErtsMonotonicTime current_time = 0;
 
-	    if (!(flgs & ERTS_SSI_FLG_WAITING)) {
-		ASSERT(!(flgs & ERTS_SSI_FLG_SLEEPING));
-		break;
-	    }
+        aux_work = erts_atomic32_read_acqb(&ssi->aux_work);
+        if (aux_work && !ERTS_SCHEDULER_IS_DIRTY(esdp)) {
+            if (!thr_prgr_active) {
+                erts_thr_progress_active(esdp, thr_prgr_active = 1);
+                sched_wall_time_change(esdp, 1);
+            }
+            aux_work = handle_aux_work(&esdp->aux_work_data, aux_work, 1);
+            ERTS_MSACC_UPDATE_CACHE();
+            if (aux_work && erts_thr_progress_update(esdp))
+                erts_thr_progress_leader_update(esdp);
+        }
 
-	    flgs = sched_prep_cont_spin_wait(ssi);
-	    spincount = sched_busy_wait.aux_work;
+        if (aux_work) {
+            if (!ERTS_SCHEDULER_IS_DIRTY(esdp)) {
+                flgs = erts_atomic32_read_acqb(&ssi->flags);
+                current_time = erts_get_monotonic_time(esdp);
+                if (current_time >= erts_next_timeout_time(esdp->next_tmo_ref)) {
+                    if (!thr_prgr_active) {
+                        erts_thr_progress_active(esdp, thr_prgr_active = 1);
+                        sched_wall_time_change(esdp, 1);
+                    }
+                    erts_bump_timers(esdp->timer_wheel, current_time);
+                }
+            }
+        }
+        else {
+            ErtsMonotonicTime timeout_time;
+            int do_timeout = 0;
+            if (!ERTS_SCHEDULER_IS_DIRTY(esdp)) {
+                timeout_time = erts_check_next_timeout_time(esdp);
+                current_time = erts_get_monotonic_time(esdp);
+                do_timeout = (current_time >= timeout_time);
+            } else {
+                current_time = 0;
+                timeout_time = ERTS_MONOTONIC_TIME_MAX;
+            }
+            if (do_timeout) {
+                if (!thr_prgr_active) {
+                    erts_thr_progress_active(esdp, thr_prgr_active = 1);
+                    sched_wall_time_change(esdp, 1);
+                }
+            }
+            else {
+                if (!ERTS_SCHEDULER_IS_DIRTY(esdp)) {
+                    if (thr_prgr_active) {
+                        erts_thr_progress_active(esdp, thr_prgr_active = 0);
+                        sched_wall_time_change(esdp, 0);
+                    }
+                    erts_thr_progress_prepare_wait(esdp);
+                }
 
-	    if (!(flgs & ERTS_SSI_FLG_WAITING)) {
-		ASSERT(!(flgs & ERTS_SSI_FLG_SLEEPING));
-		break;
-	    }
+                flgs = sched_spin_wait(ssi, spincount);
+                if (flgs & ERTS_SSI_FLG_SLEEPING) {
+                    ASSERT(flgs & ERTS_SSI_FLG_WAITING);
+                    flgs = sched_set_sleeptype(ssi, ERTS_SSI_FLG_TSE_SLEEPING);
+                    if (flgs & ERTS_SSI_FLG_SLEEPING) {
+                        int res;
+                        ASSERT(flgs & ERTS_SSI_FLG_TSE_SLEEPING);
+                        ASSERT(flgs & ERTS_SSI_FLG_WAITING);
+                        current_time = ERTS_SCHEDULER_IS_DIRTY(esdp) ? 0 :
+                            erts_get_monotonic_time(esdp);
+                        do {
+                            Sint64 timeout;
+                            if (current_time >= timeout_time)
+                                break;
+                            if (!ERTS_SCHEDULER_IS_DIRTY(esdp)) {
+                                timeout = ERTS_MONOTONIC_TO_NSEC(timeout_time
+                                                                 - current_time
+                                                                 - 1) + 1;
+                            } else
+                                timeout = -1;
+                            ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_SLEEP);
+                            res = erts_tse_twait(ssi->event, timeout);
+                            ERTS_MSACC_POP_STATE_M();
+                            current_time = ERTS_SCHEDULER_IS_DIRTY(esdp) ? 0 :
+                                erts_get_monotonic_time(esdp);
+                        } while (res == EINTR);
+                    }
+                }
+                if (!ERTS_SCHEDULER_IS_DIRTY(esdp))
+                    erts_thr_progress_finalize_wait(esdp);
+            }
+            if (!ERTS_SCHEDULER_IS_DIRTY(esdp) && current_time >= timeout_time)
+                erts_bump_timers(esdp->timer_wheel, current_time);
+        }
 
-	}
+        if (!(flgs & ERTS_SSI_FLG_WAITING)) {
+            ASSERT(!(flgs & ERTS_SSI_FLG_SLEEPING));
+            break;
+        }
 
-	if (flgs & ~(ERTS_SSI_FLG_SUSPENDED|ERTS_SSI_FLG_MSB_EXEC))
-	    erts_atomic32_read_band_nob(&ssi->flags,
-                                            (ERTS_SSI_FLG_SUSPENDED
-                                             | ERTS_SSI_FLG_MSB_EXEC));
+        flgs = sched_prep_cont_spin_wait(ssi);
+        spincount = sched_busy_wait.aux_work;
 
-	if (ERTS_SCHEDULER_IS_DIRTY(esdp))
-	    dirty_sched_wall_time_change(esdp, working = 1);
-        else if (!thr_prgr_active) {
-	    erts_thr_progress_active(esdp, thr_prgr_active = 1);
-	    sched_wall_time_change(esdp, 1);
+        if (!(flgs & ERTS_SSI_FLG_WAITING)) {
+            ASSERT(!(flgs & ERTS_SSI_FLG_SLEEPING));
+            break;
         }
 
-	erts_runq_lock(rq);
-	sched_active(esdp->no, rq);
-
     }
-    else
-    {
-
-	erts_atomic32_set_relb(&function_calls, 0);
-	*fcalls = 0;
-
-	ASSERT(!ERTS_SCHEDULER_IS_DIRTY(esdp));
-
-	sched_waiting_sys(esdp->no, rq);
-
-	erts_runq_unlock(rq);
-
-	ASSERT(working);
-	sched_wall_time_change(esdp, working = 0);
-
-	spincount = sched_busy_wait.sys_schedule;
-	if (spincount == 0)
-	    goto sys_aux_work;
-
-	while (spincount-- > 0) {
-	    ErtsMonotonicTime current_time;
-
-	sys_poll_aux_work:
-
-	    if (working)
-		sched_wall_time_change(esdp, working = 0);
-
-	    ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_CHECK_IO);
-
-	    ASSERT(!erts_port_task_have_outstanding_io_tasks());
-            LTTNG2(scheduler_poll, esdp->no, 1);
-	    erl_sys_schedule(1); /* Might give us something to do */
-
-	    ERTS_MSACC_POP_STATE_M();
-
-	    if (!ERTS_SCHEDULER_IS_DIRTY(esdp)) {
-		current_time = erts_get_monotonic_time(esdp);
-		if (current_time >= erts_next_timeout_time(esdp->next_tmo_ref))
-		    erts_bump_timers(esdp->timer_wheel, current_time);
-	    }
-
-	sys_aux_work:
-
-	    aux_work = erts_atomic32_read_acqb(&ssi->aux_work);
-	    if (aux_work && !ERTS_SCHEDULER_IS_DIRTY(esdp)) {
-		if (!working)
-		    sched_wall_time_change(esdp, working = 1);
-		if (!thr_prgr_active)
-		    erts_thr_progress_active(esdp, thr_prgr_active = 1);
-		aux_work = handle_aux_work(&esdp->aux_work_data, aux_work, 1);
-                ERTS_MSACC_UPDATE_CACHE();
-		if (aux_work && erts_thr_progress_update(esdp))
-		    erts_thr_progress_leader_update(esdp);
-	    }
-
-	    flgs = erts_atomic32_read_acqb(&ssi->flags);
-	    if (!(flgs & ERTS_SSI_FLG_WAITING)) {
-		ASSERT(!(flgs & ERTS_SSI_FLG_SLEEPING));
-		goto sys_woken;
-	    }
-
-	    /*
-	     * If we got new I/O tasks we aren't allowed to
-	     * call erl_sys_schedule() until it is handled.
-	     */
-	    if (erts_port_task_have_outstanding_io_tasks()) {
-		clear_sys_scheduling();
-		/*
-		 * Got to check that we still got I/O tasks; otherwise
-		 * we have to continue checking for I/O...
-		 */
-		if (!prepare_for_sys_schedule(0)) {
-		    spincount *= ERTS_SCHED_TSE_SLEEP_SPINCOUNT_FACT;
-		    goto tse_wait;
-		}
-	    }
-	}
-
-	erts_runq_lock(rq);
-
-	/*
-	 * If we got new I/O tasks we aren't allowed to
-	 * sleep in erl_sys_schedule().
-	 */
-	if (erts_port_task_have_outstanding_io_tasks()) {
-	    clear_sys_scheduling();
-
-	    /*
-	     * Got to check that we still got I/O tasks; otherwise
-	     * we have to wait in erl_sys_schedule() after all...
-	     */
-	    if (!prepare_for_sys_schedule(0)) {
-		/*
-		 * Not allowed to wait in erl_sys_schedule;
-		 * do tse wait instead...
-		 */
-		sched_change_waiting_sys_to_waiting(esdp->no, rq);
-		erts_runq_unlock(rq);
-		spincount = 0;
-		goto tse_wait;
-	    }
-	}
-	if (aux_work) {
-	    erts_runq_unlock(rq);
-	    goto sys_poll_aux_work;
-	}
-	flgs = sched_set_sleeptype(ssi, ERTS_SSI_FLG_POLL_SLEEPING);
-	if (!(flgs & ERTS_SSI_FLG_SLEEPING)) {
-	    if (!(flgs & ERTS_SSI_FLG_WAITING)) {
-		ASSERT(!(flgs & ERTS_SSI_FLG_SLEEPING));
-		goto sys_locked_woken;
-	    }
-	    erts_runq_unlock(rq);
-	    flgs = sched_prep_cont_spin_wait(ssi);
-	    if (!(flgs & ERTS_SSI_FLG_WAITING)) {
-		ASSERT(!(flgs & ERTS_SSI_FLG_SLEEPING));
-		goto sys_woken;
-	    }
-	    ASSERT(!erts_port_task_have_outstanding_io_tasks());
-	    goto sys_poll_aux_work;
-	}
-
-	ASSERT(flgs & ERTS_SSI_FLG_POLL_SLEEPING);
-	ASSERT(flgs & ERTS_SSI_FLG_WAITING);
-
-	erts_runq_unlock(rq);
-
-	if (working)
-	    sched_wall_time_change(esdp, working = 0);
-
-	if (thr_prgr_active)
-	    erts_thr_progress_active(esdp, thr_prgr_active = 0);
-
-	ASSERT(!erts_port_task_have_outstanding_io_tasks());
-
-	ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_CHECK_IO);
-        LTTNG2(scheduler_poll, esdp->no, 0);
 
-	erl_sys_schedule(0);
+    if (flgs & ~(ERTS_SSI_FLG_SUSPENDED|ERTS_SSI_FLG_MSB_EXEC))
+        erts_atomic32_read_band_nob(&ssi->flags,
+                                        (ERTS_SSI_FLG_SUSPENDED
+                                         | ERTS_SSI_FLG_MSB_EXEC));
 
-	ERTS_MSACC_POP_STATE_M();
-
-	if (!ERTS_SCHEDULER_IS_DIRTY(esdp)) {
-	    ErtsMonotonicTime current_time = erts_get_monotonic_time(esdp);
-	    if (current_time >= erts_next_timeout_time(esdp->next_tmo_ref))
-		erts_bump_timers(esdp->timer_wheel, current_time);
-	}
-
-	flgs = sched_prep_cont_spin_wait(ssi);
-	if (flgs & ERTS_SSI_FLG_WAITING)
-	    goto sys_aux_work;
-
-    sys_woken:
-	if (!thr_prgr_active)
-	    erts_thr_progress_active(esdp, thr_prgr_active = 1);
-	erts_runq_lock(rq);
-    sys_locked_woken:
-	if (!thr_prgr_active) {
-	    erts_runq_unlock(rq);
-	    erts_thr_progress_active(esdp, thr_prgr_active = 1);
-	    erts_runq_lock(rq);
-	}
-	clear_sys_scheduling();
-	if (flgs & ~(ERTS_SSI_FLG_SUSPENDED|ERTS_SSI_FLG_MSB_EXEC))
-	    erts_atomic32_read_band_nob(&ssi->flags,
-                                            (ERTS_SSI_FLG_SUSPENDED
-                                             | ERTS_SSI_FLG_MSB_EXEC));
-	if (!working)
-	    sched_wall_time_change(esdp, working = 1);
-	sched_active_sys(esdp->no, rq);
+    if (ERTS_SCHEDULER_IS_DIRTY(esdp))
+        dirty_sched_wall_time_change(esdp, working = 1);
+    else if (!thr_prgr_active) {
+        erts_thr_progress_active(esdp, thr_prgr_active = 1);
+        sched_wall_time_change(esdp, 1);
     }
 
+    erts_runq_lock(rq);
+    sched_active(esdp->no, rq);
+
     if (ERTS_SCHEDULER_IS_DIRTY(esdp))
         dirty_active(esdp, 1);
 
@@ -5872,6 +5730,7 @@ init_scheduler_data(ErtsSchedulerData* esdp, int num,
 	shadow_proc->static_flags = ERTS_STC_FLG_SHADOW_PROC;
     }
 
+    ssi->esdp = esdp;
     esdp->ssi = ssi;
     esdp->current_process = NULL;
     esdp->current_port = NULL;
@@ -5902,8 +5761,8 @@ init_scheduler_data(ErtsSchedulerData* esdp, int num,
 }
 
 void
-erts_init_scheduling(int no_schedulers, int no_schedulers_online
-		     , int no_dirty_cpu_schedulers, int no_dirty_cpu_schedulers_online,
+erts_init_scheduling(int no_schedulers, int no_schedulers_online, int no_poll_threads,
+		     int no_dirty_cpu_schedulers, int no_dirty_cpu_schedulers_online,
 		     int no_dirty_io_schedulers
 		     )
 {
@@ -5930,6 +5789,7 @@ erts_init_scheduling(int no_schedulers, int no_schedulers_online
     ASSERT(no_dirty_cpu_schedulers >= 1);
     ASSERT(no_dirty_cpu_schedulers_online <= no_schedulers_online);
     ASSERT(no_dirty_cpu_schedulers_online >= 1);
+    ASSERT(erts_no_poll_threads == no_poll_threads);
 
     /* Create and initialize run queues */
 
@@ -6027,7 +5887,7 @@ erts_init_scheduling(int no_schedulers, int no_schedulers_online
     erts_no_total_schedulers += no_dirty_io_schedulers;
 
     /* Create and initialize scheduler sleep info */
-    no_ssi = n+1;
+    no_ssi = n + 1 /* aux thread */;
     aligned_sched_sleep_info =
 	erts_alloc_permanent_cache_aligned(
 	    ERTS_ALC_T_SCHDLR_SLP_INFO,
@@ -6038,12 +5898,13 @@ erts_init_scheduling(int no_schedulers, int no_schedulers_online
 	ssi->next = NULL;
 	ssi->prev = NULL;
 #endif
+        ssi->esdp = NULL;
 	erts_atomic32_init_nob(&ssi->flags, 0);
 	ssi->event = NULL; /* initialized in sched_thread_func */
 	erts_atomic32_init_nob(&ssi->aux_work, 0);
     }
 
-    aligned_sched_sleep_info++;
+    aligned_sched_sleep_info += 1 /* aux thread */;
 
     aligned_dirty_cpu_sched_sleep_info =
 	erts_alloc_permanent_cache_aligned(
@@ -6066,6 +5927,18 @@ erts_init_scheduling(int no_schedulers, int no_schedulers_online
 	erts_atomic32_init_nob(&ssi->aux_work, 0);
     }
 
+    aligned_poll_thread_sleep_info =
+        erts_alloc_permanent_cache_aligned(
+	    ERTS_ALC_T_SCHDLR_SLP_INFO,
+	    no_poll_threads*sizeof(ErtsAlignedSchedulerSleepInfo));
+    for (ix = 0; ix < no_poll_threads; ix++) {
+        ErtsSchedulerSleepInfo *ssi = &aligned_poll_thread_sleep_info[ix].ssi;
+        ssi->esdp = NULL;
+	erts_atomic32_init_nob(&ssi->flags, 0);
+	ssi->event = NULL; /* initialized in poll_thread */
+	erts_atomic32_init_nob(&ssi->aux_work, 0);
+    }
+
     /* Create and initialize scheduler specific data */
 
     daww_sz = ERTS_ALC_CACHE_LINE_ALIGN_SIZE((sizeof(ErtsDelayedAuxWorkWakeupJob)
@@ -6122,11 +5995,14 @@ erts_init_scheduling(int no_schedulers, int no_schedulers_online
     erts_atomic32_init_nob(&debug_wait_completed_count, 0); /* debug only */
     debug_wait_completed_flags = 0;
 
-
     aux_thread_aux_work_data =
 	erts_alloc_permanent_cache_aligned(ERTS_ALC_T_SCHDLR_DATA,
 					   sizeof(ErtsAuxWorkData));
 
+    poll_thread_aux_work_data =
+	erts_alloc_permanent_cache_aligned(ERTS_ALC_T_SCHDLR_DATA,
+					   no_poll_threads * sizeof(ErtsAuxWorkData));
+
     init_no_runqs(no_schedulers_online, no_schedulers_online);
     balance_info.last_active_runqs = no_schedulers;
     erts_mtx_init(&balance_info.update_mtx, "migration_info_update", NIL,
@@ -6205,13 +6081,9 @@ erts_init_scheduling(int no_schedulers, int no_schedulers_online
 	erts_atomic32_set_nob(&schdlr_sspnd.changing,
 				  set_schdlr_sspnd_change_flags);
 
-    erts_atomic32_init_nob(&doing_sys_schedule, 0);
-
     init_misc_aux_work();
 
 
-    erts_atomic32_init_nob(&function_calls, 0);
-
     /* init port tasks */
     erts_port_task_init();
 
@@ -7107,17 +6979,19 @@ sched_spin_suspended(ErtsSchedulerSleepInfo *ssi, int spincount)
 }
 
 static erts_aint32_t
-sched_set_suspended_sleeptype(ErtsSchedulerSleepInfo *ssi)
+sched_set_suspended_sleeptype(ErtsSchedulerSleepInfo *ssi,
+                              erts_aint32_t sleep_type)
 {
     erts_aint32_t oflgs;
-    erts_aint32_t nflgs = (ERTS_SSI_FLG_SLEEPING
-			   | ERTS_SSI_FLG_TSE_SLEEPING
-			   | ERTS_SSI_FLG_WAITING
-			   | ERTS_SSI_FLG_SUSPENDED);
+    erts_aint32_t nflgs = ((ERTS_SSI_FLG_SLEEPING
+                            | ERTS_SSI_FLG_WAITING
+                            | ERTS_SSI_FLG_SUSPENDED)
+                           | sleep_type);
     erts_aint32_t xflgs = (ERTS_SSI_FLG_SLEEPING
 			   | ERTS_SSI_FLG_WAITING
 			   | ERTS_SSI_FLG_SUSPENDED);
 
+    ASSERT(sleep_type == ERTS_SSI_FLG_TSE_SLEEPING);
     erts_tse_reset(ssi->event);
 
     while (1) {
@@ -7370,17 +7244,6 @@ msb_scheduler_type_switch(ErtsSchedType sched_type,
     if (exec_type != ERTS_SCHED_NORMAL)
         schdlr_sspnd.last_msb_dirty_type = exec_type;
     else {
-        erts_aint32_t calls;
-        /*
-         * Going back to normal scheduler after
-         * dirty execution; make sure it will check
-         * for I/O...
-         */
-        if (ERTS_USE_MODIFIED_TIMING())
-            calls = ERTS_MODIFIED_TIMING_INPUT_REDS + 1;
-        else
-            calls = INPUT_REDUCTIONS + 1;
-        erts_atomic32_set_nob(&function_calls, calls);
 
         if ((nrml_prio == ERTS_MSB_NONE_PRIO_BIT)
             & ((dcpu_prio != ERTS_MSB_NONE_PRIO_BIT)
@@ -7454,6 +7317,34 @@ msb_scheduler_type_switch(ErtsSchedType sched_type,
 
 }
 
+static ERTS_INLINE void
+suspend_normal_scheduler_sleep(ErtsSchedulerData *esdp)
+{
+    ErtsSchedulerSleepInfo *ssi = esdp->ssi;
+    erts_aint32_t flgs = sched_spin_suspended(ssi,
+                                              ERTS_SCHED_SUSPEND_SLEEP_SPINCOUNT);
+    if (flgs == (ERTS_SSI_FLG_SLEEPING
+                 | ERTS_SSI_FLG_WAITING
+                 | ERTS_SSI_FLG_SUSPENDED)) {
+        flgs = sched_set_suspended_sleeptype(ssi, ERTS_SSI_FLG_TSE_SLEEPING);
+        if (flgs == (ERTS_SSI_FLG_SLEEPING
+                     | ERTS_SSI_FLG_TSE_SLEEPING
+                     | ERTS_SSI_FLG_WAITING
+                     | ERTS_SSI_FLG_SUSPENDED)) {
+            int res;
+
+            do {
+                res = erts_tse_wait(ssi->event);
+            } while (res == EINTR);
+        }
+    }
+}
+
+static ERTS_INLINE void
+suspend_dirty_scheduler_sleep(ErtsSchedulerData *esdp)
+{
+    suspend_normal_scheduler_sleep(esdp);
+}
 
 static void
 suspend_scheduler(ErtsSchedulerData *esdp)
@@ -7642,14 +7533,15 @@ suspend_scheduler(ErtsSchedulerData *esdp)
 	    schdlr_sspnd_resume_procs(sched_type, &resume);
 
 	    while (1) {
-		ErtsMonotonicTime current_time;
-		erts_aint32_t flgs;
-
 		if (sched_type != ERTS_SCHED_NORMAL)
-		    aux_work = 0;
-		else {
+                    suspend_dirty_scheduler_sleep(esdp);
+		else
+                {
+                    ErtsMonotonicTime current_time, timeout_time;
                     int evacuate = no == 1 ? 0 : !ERTS_EMPTY_RUNQ(esdp->run_queue);
 
+		    ASSERT(sched_type == ERTS_SCHED_NORMAL);
+
 		    aux_work = erts_atomic32_read_acqb(&ssi->aux_work);
 
 		    if (aux_work|evacuate) {
@@ -7671,95 +7563,34 @@ suspend_scheduler(ErtsSchedulerData *esdp)
 			}
 		    }
 
-		}
 
-		if (aux_work) {
-		    ASSERT(sched_type == ERTS_SCHED_NORMAL);
-		    current_time = erts_get_monotonic_time(esdp);
-		    if (current_time >= erts_next_timeout_time(esdp->next_tmo_ref)) {
-			if (!thr_prgr_active) {
-			    erts_thr_progress_active(esdp, thr_prgr_active = 1);
-			    sched_wall_time_change(esdp, 1);
-			}
-			erts_bump_timers(esdp->timer_wheel, current_time);
-		    }
-		}
-		else {
-		    ErtsMonotonicTime timeout_time;
-		    int do_timeout;
+                    if (aux_work)
+                        timeout_time = erts_next_timeout_time(esdp->next_tmo_ref);
+                    else
+                        timeout_time = erts_check_next_timeout_time(esdp);
 
-		    if (sched_type == ERTS_SCHED_NORMAL) {
-			timeout_time = erts_check_next_timeout_time(esdp);
-			current_time = erts_get_monotonic_time(esdp);
-			do_timeout = (current_time >= timeout_time);
-		    }
-		    else {
-			timeout_time = ERTS_MONOTONIC_TIME_MAX;
-			current_time = 0;
-			do_timeout = 0;
-		    }
+                    current_time = erts_get_monotonic_time(esdp);
 
-		    if (do_timeout) {
-			ASSERT(sched_type == ERTS_SCHED_NORMAL);
-			if (!thr_prgr_active) {
-			    erts_thr_progress_active(esdp, thr_prgr_active = 1);
-			    sched_wall_time_change(esdp, 1);
-			}
-		    }
-		    else {
-			if (sched_type == ERTS_SCHED_NORMAL) {
-			    if (thr_prgr_active) {
-				erts_thr_progress_active(esdp, thr_prgr_active = 0);
-				sched_wall_time_change(esdp, 0);
-			    }
-			    erts_thr_progress_prepare_wait(esdp);
-			}
-			flgs = sched_spin_suspended(ssi,
-						    ERTS_SCHED_SUSPEND_SLEEP_SPINCOUNT);
-			if (flgs == (ERTS_SSI_FLG_SLEEPING
-				     | ERTS_SSI_FLG_WAITING
-				     | ERTS_SSI_FLG_SUSPENDED)) {
-			    flgs = sched_set_suspended_sleeptype(ssi);
-			    if (flgs == (ERTS_SSI_FLG_SLEEPING
-					 | ERTS_SSI_FLG_TSE_SLEEPING
-					 | ERTS_SSI_FLG_WAITING
-					 | ERTS_SSI_FLG_SUSPENDED)) {
-				int res;
-
-				if (sched_type == ERTS_SCHED_NORMAL)
-				    current_time = erts_get_monotonic_time(esdp);
-				else
-				    current_time = 0;
-
-				do {
-				    Sint64 timeout;
-				    if (current_time >= timeout_time)
-					break;
-				    if (sched_type != ERTS_SCHED_NORMAL)
-					timeout = -1;
-				    else
-					timeout = ERTS_MONOTONIC_TO_NSEC(timeout_time
-									 - current_time
-									 - 1) + 1;
-				    res = erts_tse_twait(ssi->event, timeout);
-
-				    if (sched_type == ERTS_SCHED_NORMAL)
-					current_time = erts_get_monotonic_time(esdp);
-				    else
-					current_time = 0;
-
-				} while (res == EINTR);
-			    }
-			}
-			if (sched_type == ERTS_SCHED_NORMAL)
-			    erts_thr_progress_finalize_wait(esdp);
-		    }
+                    if (!aux_work && current_time < timeout_time) {
+                        /* go to sleep... */
+                        if (thr_prgr_active) {
+                            erts_thr_progress_active(esdp, thr_prgr_active = 0);
+                            sched_wall_time_change(esdp, 0);
+                        }
+                        erts_thr_progress_prepare_wait(NULL);
+                        suspend_normal_scheduler_sleep(esdp);
+                        erts_thr_progress_finalize_wait(NULL);
+                        current_time = erts_get_monotonic_time(esdp);
+                    }
 
-		    if (current_time >= timeout_time) {
-			ASSERT(sched_type == ERTS_SCHED_NORMAL);
-			erts_bump_timers(esdp->timer_wheel, current_time);
-		    }
-		}
+                    if (current_time >= timeout_time) {
+                        if (!thr_prgr_active) {
+                            erts_thr_progress_active(esdp, thr_prgr_active = 1);
+                            sched_wall_time_change(esdp, 1);
+                        }
+                        erts_bump_timers(esdp->timer_wheel, current_time);
+                    }
+                }
 
 		flgs = sched_prep_spin_suspended(ssi, (ERTS_SSI_FLG_WAITING
 						       | ERTS_SSI_FLG_SUSPENDED));
@@ -8425,6 +8256,7 @@ sched_thread_func(void *vesdp)
     Uint no = esdp->no;
     erts_tse_t *tse;
 
+    erts_port_task_pre_alloc_init_thread();
     erts_sched_init_time_sup(esdp);
 
     if (no == 1)
@@ -8578,17 +8410,17 @@ sched_dirty_io_thread_func(void *vesdp)
     return NULL;
 }
 
-static ethr_tid aux_tid;
-
 void
 erts_start_schedulers(void)
 {
+    ethr_tid tid;
     int res = 0;
     Uint actual;
     Uint wanted = erts_no_schedulers;
     Uint wanted_no_schedulers = erts_no_schedulers;
     char name[16];
     ethr_thr_opts opts = ETHR_THR_OPTS_DEFAULT_INITER;
+    int ix;
 
     opts.detached = 1;
 
@@ -8635,7 +8467,6 @@ erts_start_schedulers(void)
     erts_no_schedulers = actual;
 
     {
-	int ix;
 	for (ix = 0; ix < erts_no_dirty_cpu_schedulers; ix++) {
 	    ErtsSchedulerData *esdp = ERTS_DIRTY_CPU_SCHEDULER_IX(ix);
 	    erts_snprintf(opts.name, 16, "%d_dirty_cpu_scheduler", ix + 1);
@@ -8658,10 +8489,18 @@ erts_start_schedulers(void)
 
     erts_snprintf(opts.name, 16, "aux");
 
-    res = ethr_thr_create(&aux_tid, aux_thread, NULL, &opts);
+    res = ethr_thr_create(&tid, aux_thread, NULL, &opts);
     if (res != 0)
 	erts_exit(ERTS_ERROR_EXIT, "Failed to create aux thread, error = %d\n", res);
 
+    for (ix = 0; ix < erts_no_poll_threads; ix++) {
+        erts_snprintf(opts.name, 16, "%d_poller", ix);
+
+        res = ethr_thr_create(&tid, poll_thread, (void*)(UWord)ix, &opts);
+        if (res != 0)
+            erts_exit(ERTS_ERROR_EXIT, "Failed to create poll thread\n");
+    }
+
     if (actual < 1)
 	erts_exit(ERTS_ERROR_EXIT,
 		 "Failed to create any scheduler-threads: %s (%d)\n",
@@ -9728,7 +9567,6 @@ Process *erts_schedule(ErtsSchedulerData *esdp, Process *p, int calls)
     ErtsRunQueue *rq;
     int context_reds;
     int fcalls;
-    int input_reductions;
     int actual_reds;
     int reds;
     Uint32 flags;
@@ -9748,11 +9586,9 @@ Process *erts_schedule(ErtsSchedulerData *esdp, Process *p, int calls)
 
     if (ERTS_USE_MODIFIED_TIMING()) {
 	context_reds = ERTS_MODIFIED_TIMING_CONTEXT_REDS;
-	input_reductions = ERTS_MODIFIED_TIMING_INPUT_REDS;
     }
     else {
 	context_reds = CONTEXT_REDS;
-	input_reductions = INPUT_REDUCTIONS;
     }
 
     ERTS_LC_ASSERT(ERTS_SCHEDULER_IS_DIRTY(erts_get_scheduler_data())
@@ -9772,7 +9608,6 @@ Process *erts_schedule(ErtsSchedulerData *esdp, Process *p, int calls)
 	}
 	rq = erts_get_runq_current(esdp);
 	ASSERT(esdp);
-	fcalls = (int) erts_atomic32_read_acqb(&function_calls);
 	actual_reds = reds = 0;
 	erts_runq_lock(rq);
     } else {
@@ -9798,7 +9633,6 @@ Process *erts_schedule(ErtsSchedulerData *esdp, Process *p, int calls)
 	    reds = ERTS_PROC_MIN_CONTEXT_SWITCH_REDS_COST;
 	esdp->virtual_reds = 0;
 
-	fcalls = (int) erts_atomic32_add_read_acqb(&function_calls, reds);
 	ASSERT(esdp && esdp == erts_get_scheduler_data());
 
 	rq = erts_get_runq_current(esdp);
@@ -9888,16 +9722,6 @@ Process *erts_schedule(ErtsSchedulerData *esdp, Process *p, int calls)
 
 	ERTS_CHK_NO_PROC_LOCKS;
 
-	if (is_normal_sched) {
-	    if (esdp->check_time_reds >= ERTS_CHECK_TIME_REDS)
-		(void) erts_get_monotonic_time(esdp);
-
-	    if (esdp->last_monotonic_time >= erts_next_timeout_time(esdp->next_tmo_ref)) {
-		erts_runq_unlock(rq);
-		erts_bump_timers(esdp->timer_wheel, esdp->last_monotonic_time);
-		erts_runq_lock(rq);
-	    }
-	}
     }
 
     ERTS_LC_ASSERT(!is_normal_sched || !erts_thr_progress_is_blocking());
@@ -9908,6 +9732,16 @@ Process *erts_schedule(ErtsSchedulerData *esdp, Process *p, int calls)
 	ErtsMigrationPath *mp;
 
 	if (is_normal_sched) {
+
+	    if (esdp->check_time_reds >= ERTS_CHECK_TIME_REDS)
+		(void) erts_get_monotonic_time(esdp);
+
+	    if (esdp->last_monotonic_time >= erts_next_timeout_time(esdp->next_tmo_ref)) {
+		erts_runq_unlock(rq);
+		erts_bump_timers(esdp->timer_wheel, esdp->last_monotonic_time);
+		erts_runq_lock(rq);
+	    }
+
 	    if (rq->check_balance_reds <= 0)
 		check_balance(rq);
 
@@ -10037,38 +9871,6 @@ Process *erts_schedule(ErtsSchedulerData *esdp, Process *p, int calls)
 
 	    goto check_activities_to_run;
 	}
-	else if (is_normal_sched
-		 && (fcalls > input_reductions
-		     && prepare_for_sys_schedule(!0))) {
-	    ErtsMonotonicTime current_time;
-	    /*
-	     * Schedule system-level activities.
-	     */
-
-	    ERTS_MSACC_PUSH_STATE_CACHED_M();
-
-	    erts_atomic32_set_relb(&function_calls, 0);
-	    fcalls = 0;
-
-#if 0 /* Not needed since we wont wait in sys schedule */
-	    erts_sys_schedule_interrupt(0);
-#endif
-	    erts_runq_unlock(rq);
-
-            ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_CHECK_IO);
-            LTTNG2(scheduler_poll, esdp->no, 1);
-
-	    erl_sys_schedule(1);
-	    ERTS_MSACC_POP_STATE_M();
-
-	    current_time = erts_get_monotonic_time(esdp);
-	    if (current_time >= erts_next_timeout_time(esdp->next_tmo_ref))
-		erts_bump_timers(esdp->timer_wheel, current_time);
-
-	    erts_runq_lock(rq);
-	    clear_sys_scheduling();
-	    goto continue_check_activities_to_run;
-	}
 
         if (flags & ERTS_RUNQ_FLG_MISC_OP)
 	    exec_misc_ops(rq);
@@ -10082,29 +9884,9 @@ Process *erts_schedule(ErtsSchedulerData *esdp, Process *p, int calls)
         flags = ERTS_RUNQ_FLGS_GET_NOB(rq);
 
 	if (flags & PORT_BIT) {
-	    int have_outstanding_io;
-	    have_outstanding_io = erts_port_task_execute(rq, &esdp->current_port);
-	    if ((!erts_eager_check_io
-		 && have_outstanding_io
-		 && fcalls > 2*input_reductions)
-		|| (flags & ERTS_RUNQ_FLG_HALTING)) {
-		/*
-		 * If we have performed more than 2*INPUT_REDUCTIONS since
-		 * last call to erl_sys_schedule() and we still haven't
-		 * handled all I/O tasks we stop running processes and
-		 * focus completely on ports.
-		 *
-		 * One could argue that this is a strange behavior. The
-		 * reason for doing it this way is that it is similar
-		 * to the behavior before port tasks were introduced.
-		 * We don't want to change the behavior too much, at
-		 * least not at the time of writing. This behavior
-		 * might change in the future.
-		 *
-		 * /rickard
-		 */
-		goto check_activities_to_run;
-	    }
+	    erts_port_task_execute(rq, &esdp->current_port);
+            if (flags & ERTS_RUNQ_FLG_HALTING)
+                goto check_activities_to_run;
 	}
 
 	/*
diff --git a/erts/emulator/beam/erl_process.h b/erts/emulator/beam/erl_process.h
index e63da2d9db..66d7848f89 100644
--- a/erts/emulator/beam/erl_process.h
+++ b/erts/emulator/beam/erl_process.h
@@ -105,7 +105,6 @@ struct saved_calls {
 };
 
 extern Export exp_send, exp_receive, exp_timeout;
-extern int erts_eager_check_io;
 extern int erts_sched_compact_load;
 extern int erts_sched_balance_util;
 extern Uint erts_no_schedulers;
@@ -364,10 +363,12 @@ typedef struct {
 } ErtsSchedulerSleepList;
 
 struct ErtsSchedulerSleepInfo_ {
+    struct ErtsSchedulerData_ *esdp;
     ErtsSchedulerSleepInfo *next;
     ErtsSchedulerSleepInfo *prev;
     erts_atomic32_t flags;
     erts_tse_t *event;
+    struct erts_poll_thread *psi;
     erts_atomic32_t aux_work;
 };
 
@@ -1531,9 +1532,7 @@ extern int erts_system_profile_ts_type;
 void erts_pre_init_process(void);
 void erts_late_init_process(void);
 void erts_early_init_scheduling(int);
-void erts_init_scheduling(int, int
-			  , int, int, int
-			  );
+void erts_init_scheduling(int, int, int, int, int, int);
 void erts_execute_dirty_system_task(Process *c_p);
 int erts_set_gc_state(Process *c_p, int enable);
 Eterm erts_sched_wall_time_request(Process *c_p, int set, int enable,
@@ -2470,6 +2469,7 @@ void erts_notify_inc_runq(ErtsRunQueue *runq);
 
 void erts_sched_finish_poke(ErtsSchedulerSleepInfo *, erts_aint32_t);
 ERTS_GLB_INLINE void erts_sched_poke(ErtsSchedulerSleepInfo *ssi);
+void erts_aux_thread_poke(void);
 
 #if ERTS_GLB_INLINE_INCL_FUNC_DEF
 
diff --git a/erts/emulator/beam/erl_sched_spec_pre_alloc.c b/erts/emulator/beam/erl_sched_spec_pre_alloc.c
index 6cb7ccab8d..ab204303d7 100644
--- a/erts/emulator/beam/erl_sched_spec_pre_alloc.c
+++ b/erts/emulator/beam/erl_sched_spec_pre_alloc.c
@@ -37,7 +37,7 @@
 #include "erl_thr_progress.h"
 
 erts_sspa_data_t *
-erts_sspa_create(size_t blk_sz, int pa_size)
+erts_sspa_create(size_t blk_sz, int pa_size, int nthreads, const char* name)
 {
     erts_sspa_data_t *data;
     size_t tot_size;
@@ -48,22 +48,30 @@ erts_sspa_create(size_t blk_sz, int pa_size)
     int no_blocks = pa_size;
     int no_blocks_per_chunk;
 
-    if (erts_no_schedulers == 1)
+    if (!name) { /* schedulers only variant */
+        ASSERT(!nthreads);
+        nthreads = erts_no_schedulers;
+    }
+    else {
+        ASSERT(nthreads > 0);
+    }
+
+    if (nthreads == 1)
 	no_blocks_per_chunk = no_blocks;
     else {
 	int extra = (no_blocks - 1)/4 + 1;
 	if (extra == 0)
 	    extra = 1;
 	no_blocks_per_chunk = no_blocks;
-	no_blocks_per_chunk += extra*erts_no_schedulers;
-	no_blocks_per_chunk /= erts_no_schedulers;
+	no_blocks_per_chunk += extra * nthreads;
+	no_blocks_per_chunk /= nthreads;
     }
-    no_blocks = no_blocks_per_chunk * erts_no_schedulers;
+    no_blocks = no_blocks_per_chunk * nthreads;
     chunk_mem_size = ERTS_ALC_CACHE_LINE_ALIGN_SIZE(sizeof(erts_sspa_chunk_header_t));
     chunk_mem_size += blk_sz * no_blocks_per_chunk;
     chunk_mem_size = ERTS_ALC_CACHE_LINE_ALIGN_SIZE(chunk_mem_size);
     tot_size = ERTS_ALC_CACHE_LINE_ALIGN_SIZE(sizeof(erts_sspa_data_t));
-    tot_size += chunk_mem_size*erts_no_schedulers;
+    tot_size += chunk_mem_size * nthreads;
 
     p = erts_alloc_permanent_cache_aligned(ERTS_ALC_T_PRE_ALLOC_DATA, tot_size);
     data = (erts_sspa_data_t *) p;
@@ -72,10 +80,16 @@ erts_sspa_create(size_t blk_sz, int pa_size)
 
     data->chunks_mem_size = chunk_mem_size;
     data->start = chunk_start;
-    data->end = chunk_start + chunk_mem_size*erts_no_schedulers;
+    data->end = chunk_start + chunk_mem_size * nthreads;
+    data->nthreads = nthreads;
+
+    if (name) { /* thread variant */
+        erts_tsd_key_create(&data->tsd_key, (char*)name);
+        erts_atomic_init_nob(&data->id_generator, 0);
+    }
 
     /* Initialize all chunks */
-    for (cix = 0; cix < erts_no_schedulers; cix++) {
+    for (cix = 0; cix < nthreads; cix++) {
 	erts_sspa_chunk_t *chnk = erts_sspa_cix2chunk(data, cix);
 	erts_sspa_chunk_header_t *chdr = &chnk->aligned.header;
 	erts_sspa_blk_t *blk;
diff --git a/erts/emulator/beam/erl_sched_spec_pre_alloc.h b/erts/emulator/beam/erl_sched_spec_pre_alloc.h
index 1307e65962..d232db0e69 100644
--- a/erts/emulator/beam/erl_sched_spec_pre_alloc.h
+++ b/erts/emulator/beam/erl_sched_spec_pre_alloc.h
@@ -59,6 +59,11 @@ typedef struct {
     char *start;
     char *end;
     int chunks_mem_size;
+    int nthreads;
+
+    /* Used only by thread variant: */
+    erts_tsd_key_t tsd_key;
+    erts_atomic_t id_generator;
 } erts_sspa_data_t;
 
 typedef union erts_sspa_blk_t_ erts_sspa_blk_t;
@@ -140,7 +145,9 @@ check_local_list(erts_sspa_chunk_header_t *chdr)
 #endif
 
 erts_sspa_data_t *erts_sspa_create(size_t blk_sz,
-				   int pa_size);
+				   int pa_size,
+                                   int nthreads,
+                                   const char* name);
 void erts_sspa_remote_free(erts_sspa_chunk_header_t *chdr,
 			   erts_sspa_blk_t *blk,
 			   int cinit);
@@ -158,7 +165,7 @@ ERTS_GLB_INLINE int erts_sspa_free(erts_sspa_data_t *data, int cix, char *blk);
 ERTS_GLB_INLINE erts_sspa_chunk_t *
 erts_sspa_cix2chunk(erts_sspa_data_t *data, int cix)
 {
-    ASSERT(0 <= cix && cix < erts_no_schedulers);
+    ASSERT(0 <= cix && cix < data->nthreads);
     return (erts_sspa_chunk_t *) (data->start + cix*data->chunks_mem_size);
 }
 
@@ -171,7 +178,7 @@ erts_sspa_ptr2cix(erts_sspa_data_t *data, void *ptr)
 	return -1;
     diff = ((char *) ptr) - data->start;
     cix = (int) diff / data->chunks_mem_size;
-    ASSERT(0 <= cix && cix < erts_no_schedulers);
+    ASSERT(0 <= cix && cix < data->nthreads);
     return cix;
 }
 
diff --git a/erts/emulator/beam/erl_threads.h b/erts/emulator/beam/erl_threads.h
index e306df818d..aedceb6fc2 100644
--- a/erts/emulator/beam/erl_threads.h
+++ b/erts/emulator/beam/erl_threads.h
@@ -454,7 +454,6 @@ ERTS_GLB_INLINE void erts_rwmtx_runlock(erts_rwmtx_t *rwmtx);
 ERTS_GLB_INLINE void erts_rwmtx_rwunlock(erts_rwmtx_t *rwmtx);
 ERTS_GLB_INLINE int erts_lc_rwmtx_is_rlocked(erts_rwmtx_t *mtx);
 ERTS_GLB_INLINE int erts_lc_rwmtx_is_rwlocked(erts_rwmtx_t *mtx);
-
 ERTS_GLB_INLINE void erts_spinlock_init(erts_spinlock_t *lock,
                                         char *name,
                                         Eterm extra,
diff --git a/erts/emulator/beam/erl_trace.c b/erts/emulator/beam/erl_trace.c
index a07e3642f6..4b996d8fc2 100644
--- a/erts/emulator/beam/erl_trace.c
+++ b/erts/emulator/beam/erl_trace.c
@@ -1449,7 +1449,6 @@ monitor_long_schedule_port(Port *pp, ErtsPortTaskType type, Uint time)
     case ERTS_PORT_TASK_TIMEOUT: op = am_timeout; break;
     case ERTS_PORT_TASK_INPUT: op = am_input; break;
     case ERTS_PORT_TASK_OUTPUT: op = am_output; break;
-    case ERTS_PORT_TASK_EVENT: op = am_event; break;
     case ERTS_PORT_TASK_DIST_CMD: op = am_dist_cmd; break;
     default: op = am_undefined; break;
     }
diff --git a/erts/emulator/beam/erl_vm.h b/erts/emulator/beam/erl_vm.h
index 076767c7cd..295130f60c 100644
--- a/erts/emulator/beam/erl_vm.h
+++ b/erts/emulator/beam/erl_vm.h
@@ -46,8 +46,6 @@
  */
 #define ERTS_X_REGS_ALLOCATED (MAX_REG+3)
 
-#define INPUT_REDUCTIONS (2 * CONTEXT_REDS)
-
 #define H_DEFAULT_SIZE  233        /* default (heap + stack) min size */
 #define VH_DEFAULT_SIZE  32768     /* default virtual (bin) heap min size (words) */
 #define H_DEFAULT_MAX_SIZE 0       /* default max heap size is off */
diff --git a/erts/emulator/beam/erlang_lttng.h b/erts/emulator/beam/erlang_lttng.h
index 4e869671f7..feb05f4f4c 100644
--- a/erts/emulator/beam/erlang_lttng.h
+++ b/erts/emulator/beam/erlang_lttng.h
@@ -159,21 +159,6 @@ TRACEPOINT_EVENT(
 
 TRACEPOINT_EVENT(
     org_erlang_otp,
-    driver_event,
-    TP_ARGS(
-        char*, pid,
-        char*, port,
-        char*, driver
-    ),
-    TP_FIELDS(
-        ctf_string(pid, pid)
-        ctf_string(port, port)
-        ctf_string(driver, driver)
-    )
-)
-
-TRACEPOINT_EVENT(
-    org_erlang_otp,
     driver_timeout,
     TP_ARGS(
         char*, pid,
diff --git a/erts/emulator/beam/global.h b/erts/emulator/beam/global.h
index 2b0ad0b98a..09aeba00fa 100644
--- a/erts/emulator/beam/global.h
+++ b/erts/emulator/beam/global.h
@@ -222,8 +222,6 @@ struct erts_driver_t_ {
 			 char *buf, ErlDrvSizeT len,
 			 char **rbuf, ErlDrvSizeT rlen, /* Might be NULL */
 			 unsigned int *flags);
-    void (*event)(ErlDrvData drv_data, ErlDrvEvent event,
-		  ErlDrvEventData event_data);
     void (*ready_input)(ErlDrvData drv_data, ErlDrvEvent event); 
     void (*ready_output)(ErlDrvData drv_data, ErlDrvEvent event);  
     void (*timeout)(ErlDrvData drv_data);
@@ -1103,7 +1101,6 @@ void erts_save_stacktrace(Process* p, struct StackTrace* s, int depth);
 typedef struct {
     Eterm delay_time;
     int context_reds;
-    int input_reds;
 } ErtsModifiedTimings;
 
 extern Export *erts_delay_trap;
diff --git a/erts/emulator/beam/io.c b/erts/emulator/beam/io.c
index bc1b9b6ef4..85013af3ad 100644
--- a/erts/emulator/beam/io.c
+++ b/erts/emulator/beam/io.c
@@ -5390,24 +5390,17 @@ erts_stale_drv_select(Eterm port,
     switch (mode) {
     case ERL_DRV_READ | ERL_DRV_WRITE:
 	type = "Input/Output";
-	goto deselect;
     case ERL_DRV_WRITE:
 	type = "Output";
-	goto deselect;
     case ERL_DRV_READ:
 	type = "Input";
-    deselect:
-	if (deselect) {
-	    driver_select(drv_port, hndl,
-			  mode | ERL_DRV_USE_NO_CALLBACK,
-			  0);
-	}
-	break;
     default:
-	type = "Event";
-	if (deselect)
-	    driver_event(drv_port, hndl, NULL);
-	break;
+        type = "";
+    }
+    if (deselect) {
+        driver_select(drv_port, hndl,
+                      mode | ERL_DRV_USE_NO_CALLBACK,
+                      0);
     }
 
     dsbufp = erts_create_logger_dsbuf();
@@ -7511,14 +7504,6 @@ no_output_callback(ErlDrvData drv_data, char *buf, ErlDrvSizeT len)
 }
 
 static void
-no_event_callback(ErlDrvData drv_data, ErlDrvEvent event, ErlDrvEventData event_data)
-{
-    Port *prt = get_current_port();
-    report_missing_drv_callback(prt, "Event", "event()");
-    driver_event(ERTS_Port2ErlDrvPort(prt), event, NULL);
-}
-
-static void
 no_ready_input_callback(ErlDrvData drv_data, ErlDrvEvent event)
 {
     Port *prt = get_current_port();
@@ -7585,7 +7570,6 @@ init_driver(erts_driver_t *drv, ErlDrvEntry *de, DE_Handle *handle)
     drv->outputv = de->outputv;
     drv->control = de->control;
     drv->call = de->call;
-    drv->event = de->event ? de->event : no_event_callback;
     drv->ready_input = de->ready_input ? de->ready_input : no_ready_input_callback;
     drv->ready_output = de->ready_output ? de->ready_output : no_ready_output_callback;
     drv->timeout = de->timeout ? de->timeout : no_timeout_callback;
diff --git a/erts/emulator/beam/safe_hash.c b/erts/emulator/beam/safe_hash.c
index ac9ebd4714..73306030ae 100644
--- a/erts/emulator/beam/safe_hash.c
+++ b/erts/emulator/beam/safe_hash.c
@@ -260,16 +260,17 @@ void* safe_hash_erase(SafeHash* h, void* tmpl)
 }
 
 /*
-** Call 'func(obj,func_arg2)' for all objects in table. NOT SAFE!!!
+** Call 'func(obj,func_arg2,func_arg3)' for all objects in table. NOT SAFE!!!
 */
-void safe_hash_for_each(SafeHash* h, void (*func)(void *, void *), void *func_arg2)
+void safe_hash_for_each(SafeHash* h, void (*func)(void *, void *, void *),
+                        void *func_arg2, void *func_arg3)
 {
     int i;
 
     for (i = 0; i <= h->size_mask; i++) {
 	SafeHashBucket* b = h->tab[i];
 	while (b != NULL) {
-	    (*func)((void *) b, func_arg2);
+	    (*func)((void *) b, func_arg2, func_arg3);
 	    b = b->next;
 	}
     }
diff --git a/erts/emulator/beam/safe_hash.h b/erts/emulator/beam/safe_hash.h
index 259c58cff9..af97b4cb4d 100644
--- a/erts/emulator/beam/safe_hash.h
+++ b/erts/emulator/beam/safe_hash.h
@@ -95,7 +95,7 @@ void* safe_hash_get(SafeHash*, void*);
 void* safe_hash_put(SafeHash*, void*);
 void* safe_hash_erase(SafeHash*, void*);
 
-void  safe_hash_for_each(SafeHash*, void (*func)(void *, void *), void *);
+void  safe_hash_for_each(SafeHash*, void (*func)(void *, void *, void *), void *, void *);
 
 #ifdef ERTS_ENABLE_LOCK_COUNT
 void erts_lcnt_enable_hash_lock_count(SafeHash*, erts_lock_flags_t, int);
diff --git a/erts/emulator/beam/sys.h b/erts/emulator/beam/sys.h
index 68ef0a23f3..9106091ca6 100644
--- a/erts/emulator/beam/sys.h
+++ b/erts/emulator/beam/sys.h
@@ -575,8 +575,6 @@ __decl_noreturn void __noreturn erts_exit(int n, char*, ...);
     erts_exit(ERTS_ABORT_EXIT, "%s:%d:%s(): Internal error: %s\n", \
 	     __FILE__, __LINE__, __func__, What)
 
-Eterm erts_check_io_info(void *p);
-
 UWord erts_sys_get_page_size(void);
 
 /* Size of misc memory allocated from system dependent code */
@@ -739,8 +737,6 @@ extern char *erts_sys_ddll_error(int code);
 /*
  * System interfaces for startup.
  */
-void erts_sys_schedule_interrupt(int set);
-void erts_sys_schedule_interrupt_timed(int, ErtsMonotonicTime);
 void erts_sys_main_thread(void);
 
 extern int erts_sys_prepare_crash_dump(int secs);
@@ -794,7 +790,7 @@ void fini_getenv_state(GETENV_STATE *);
 typedef struct {
     int no_used_fds;
     int no_driver_select_structs;
-    int no_driver_event_structs;
+    int no_enif_select_structs;
 } ErtsCheckIoDebugInfo;
 int erts_check_io_debug(ErtsCheckIoDebugInfo *ip);
 
@@ -996,10 +992,6 @@ erts_refc_read(erts_refc_t *refcp, erts_aint_t min_val)
 
 #endif /* #if ERTS_GLB_INLINE_INCL_FUNC_DEF */
 
-#ifdef ERTS_ENABLE_KERNEL_POLL
-extern int erts_use_kernel_poll;
-#endif
-
 #define sys_memcpy(s1,s2,n)  memcpy(s1,s2,n)
 #define sys_memmove(s1,s2,n) memmove(s1,s2,n)
 #define sys_memcmp(s1,s2,n)  memcmp(s1,s2,n)
diff --git a/erts/emulator/sys/common/erl_check_io.c b/erts/emulator/sys/common/erl_check_io.c
index 834b77eb58..f93d4c1557 100644
--- a/erts/emulator/sys/common/erl_check_io.c
+++ b/erts/emulator/sys/common/erl_check_io.c
@@ -29,7 +29,6 @@
 #endif
 
 #define ERL_CHECK_IO_C__
-#define ERTS_WANT_BREAK_HANDLING
 #ifndef WANT_NONBLOCKING
 #  define WANT_NONBLOCKING
 #endif
@@ -44,71 +43,79 @@
 #define ERTS_WANT_TIMER_WHEEL_API
 #include "erl_time.h"
 
-#ifndef ERTS_SYS_CONTINOUS_FD_NUMBERS
-#  include "safe_hash.h"
-#  define DRV_EV_STATE_HTAB_SIZE 1024
+#if 0
+#define DEBUG_PRINT(FMT, ...) erts_printf(FMT "\r\n", ##__VA_ARGS__)
+#define DEBUG_PRINT_FD(FMT, STATE, ...)                                 \
+    DEBUG_PRINT("%d: " FMT " (ev=%s, ac=%s, flg=%d)",                   \
+                (STATE) ? (STATE)->fd : (ErtsSysFdType)-1, ##__VA_ARGS__, \
+                ev2str((STATE) ? (STATE)->events : ERTS_POLL_EV_NONE),  \
+                ev2str((STATE) ? (STATE)->active_events : ERTS_POLL_EV_NONE), \
+                (STATE) ? (STATE)->flags : ERTS_EV_FLAG_CLEAR)
+#define DEBUG_PRINT_MODE
+#else
+#define DEBUG_PRINT(...)
 #endif
 
-typedef char EventStateType;
-#define ERTS_EV_TYPE_NONE     ((EventStateType) 0)
-#define ERTS_EV_TYPE_DRV_SEL  ((EventStateType) 1) /* driver_select */
-#define ERTS_EV_TYPE_DRV_EV   ((EventStateType) 2) /* driver_event */
-#define ERTS_EV_TYPE_STOP_USE ((EventStateType) 3) /* pending stop_select */
-#define ERTS_EV_TYPE_NIF      ((EventStateType) 4) /* enif_select */
-#define ERTS_EV_TYPE_STOP_NIF ((EventStateType) 5) /* pending nif stop */
-
-typedef char EventStateFlags;
-#define ERTS_EV_FLAG_USED         ((EventStateFlags) 1)   /* ERL_DRV_USE has been turned on */
-#define ERTS_EV_FLAG_DEFER_IN_EV  ((EventStateFlags) 2)
-#define ERTS_EV_FLAG_DEFER_OUT_EV ((EventStateFlags) 4)
-
-#ifdef DEBUG
-#  define ERTS_ACTIVE_FD_INC 2
-#else
-#  define ERTS_ACTIVE_FD_INC 128
+#ifndef DEBUG_PRINT_FD
+#define DEBUG_PRINT_FD(...)
 #endif
 
-#define ERTS_CHECK_IO_POLL_RES_LEN 512
+#ifndef ERTS_SYS_CONTINOUS_FD_NUMBERS
+#  include "safe_hash.h"
+#  define DRV_EV_STATE_HTAB_SIZE 1024
+#endif
 
-#if defined(ERTS_KERNEL_POLL_VERSION)
-#  define ERTS_CIO_EXPORT(FUNC) FUNC ## _kp
-#elif defined(ERTS_NO_KERNEL_POLL_VERSION)
-#  define ERTS_CIO_EXPORT(FUNC) FUNC ## _nkp
+typedef enum {
+    ERTS_EV_TYPE_NONE     = 0,
+    ERTS_EV_TYPE_DRV_SEL  = 1, /* driver_select */
+    ERTS_EV_TYPE_STOP_USE = 2, /* pending stop_select */
+    ERTS_EV_TYPE_NIF      = 3, /* enif_select */
+    ERTS_EV_TYPE_STOP_NIF = 4  /* pending nif stop */
+} EventStateType;
+
+typedef enum {
+    ERTS_EV_FLAG_CLEAR         = 0,
+    ERTS_EV_FLAG_USED          = 1,   /* ERL_DRV_USE has been turned on */
+#ifdef ERTS_ENABLE_KERNEL_POLL
+    ERTS_EV_FLAG_FALLBACK      = 2,   /* Set when kernel poll rejected fd
+                                         and it was put in the nkp version */
 #else
-#  define ERTS_CIO_EXPORT(FUNC) FUNC
+    ERTS_EV_FLAG_FALLBACK      = ERTS_EV_FLAG_CLEAR,
 #endif
 
-#define ERTS_CIO_HAVE_DRV_EVENT \
-  (ERTS_POLL_USE_POLL && !ERTS_POLL_USE_KERNEL_POLL)
+    /* Combinations */
+    ERTS_EV_FLAG_USED_FALLBACK = ERTS_EV_FLAG_USED | ERTS_EV_FLAG_FALLBACK
+} EventStateFlags;
 
-#define ERTS_CIO_POLL_CTL	ERTS_POLL_EXPORT(erts_poll_control)
-#define ERTS_CIO_POLL_CTLV	ERTS_POLL_EXPORT(erts_poll_controlv)
-#define ERTS_CIO_POLL_WAIT	ERTS_POLL_EXPORT(erts_poll_wait)
-#define ERTS_CIO_POLL_INTR 	ERTS_POLL_EXPORT(erts_poll_interrupt)
-#define ERTS_CIO_POLL_INTR_TMD	ERTS_POLL_EXPORT(erts_poll_interrupt_timed)
-#define ERTS_CIO_NEW_POLLSET 	ERTS_POLL_EXPORT(erts_poll_create_pollset)
-#define ERTS_CIO_FREE_POLLSET	ERTS_POLL_EXPORT(erts_poll_destroy_pollset)
-#define ERTS_CIO_POLL_MAX_FDS	ERTS_POLL_EXPORT(erts_poll_max_fds)
-#define ERTS_CIO_POLL_INIT	ERTS_POLL_EXPORT(erts_poll_init)
-#define ERTS_CIO_POLL_INFO	ERTS_POLL_EXPORT(erts_poll_info)
+#define flag2str(flags)                                                 \
+    ((flags) == ERTS_EV_FLAG_CLEAR ? "CLEAR" :                          \
+     ((flags) == ERTS_EV_FLAG_USED ? "USED" :                           \
+      ((flags) == ERTS_EV_FLAG_FALLBACK ? "FLBK" :                      \
+       ((flags) == ERTS_EV_FLAG_USED_FALLBACK ? "USED|FLBK" : "ERROR"))))
 
-#define GET_FD(fd) fd
+/* How many events that can be handled at once by one erts_poll_wait call */
+#define ERTS_CHECK_IO_POLL_RES_LEN 512
 
-static struct pollset_info
+/* Each I/O Poll Thread has one ErtsPollThread each. The ps field
+   can point to either a private ErtsPollSet or a shared one.
+   At the moment only kqueue and epoll pollsets can be
+   shared across threads.
+*/
+typedef struct erts_poll_thread
 {
-    ErtsPollSet ps;
-    erts_atomic_t in_poll_wait;        /* set while doing poll */
-    struct {
-	int six; /* start index */
-	int eix; /* end index */
-	erts_atomic32_t no;
-	int size;
-	ErtsSysFdType *array;
-    } active_fd;
-    struct removed_fd* removed_list;       /* list of deselected fd's*/
-    erts_spinlock_t removed_list_lock;
-}pollset;
-#define NUM_OF_POLLSETS 1
+    ErtsPollSet *ps;
+    ErtsPollResFd *pollres;
+    int pollres_len;
+} ErtsPollThread;
+
+/* pollsetv contains pointers to the ErtsPollSets that are in use.
+ * Which pollset to use is determined by hashing the fd.
+ */
+static ErtsPollSet **pollsetv;
+#if ERTS_POLL_USE_FALLBACK
+static ErtsPollSet *flbk_pollset;
+#endif
+static ErtsPollThread *psiv;
 
 typedef struct {
 #ifndef ERTS_SYS_CONTINOUS_FD_NUMBERS
@@ -117,92 +124,151 @@ typedef struct {
     ErtsSysFdType fd;
     struct {
 	ErtsDrvSelectDataState *select;   /* ERTS_EV_TYPE_DRV_SEL */
-#if ERTS_CIO_HAVE_DRV_EVENT
-	ErtsDrvEventDataState *event;     /* ERTS_EV_TYPE_DRV_EV */
-#endif
         ErtsNifSelectDataState *nif;      /* ERTS_EV_TYPE_NIF */
         union {
             erts_driver_t*  drv_ptr;    /* ERTS_EV_TYPE_STOP_USE */
             ErtsResource* resource;   /* ERTS_EV_TYPE_STOP_NIF */
-        }stop;
+        } stop;
     } driver;
-    ErtsPollEvents events;
-    unsigned short remove_cnt; /* number of removed_fd's referring to this fd */
+    ErtsPollEvents events; /* The events that have been selected upon */
+    ErtsPollEvents active_events; /* The events currently active in the pollset */
     EventStateType type;
     EventStateFlags flags;
 } ErtsDrvEventState;
 
-struct removed_fd {
-    struct removed_fd *next;
+struct drv_ev_state_shared {
+
+    union {
+        erts_mtx_t lck;
+        byte _cache_line_alignment[ERTS_ALC_CACHE_LINE_ALIGN_SIZE(sizeof(erts_mtx_t))];
+    } locks[ERTS_CHECK_IO_DRV_EV_STATE_LOCK_CNT];
+
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    ErtsSysFdType fd;
+    int max_fds;
+    erts_atomic_t len;
+    ErtsDrvEventState *v;
+    erts_mtx_t grow_lock; /* prevent lock-hogging of racing growers */
 #else
-    ErtsDrvEventState* state;
-    #ifdef DEBUG
-    ErtsSysFdType fd;
-    #endif
+    SafeHash tab;
+    int num_prealloc;
+    ErtsDrvEventState *prealloc_first;
+    erts_spinlock_t prealloc_lock;
 #endif
-
 };
 
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-static int max_fds = -1;
-#endif
-#define DRV_EV_STATE_LOCK_CNT 16
-static union {
-    erts_mtx_t lck;
-    byte _cache_line_alignment[64];
-}drv_ev_state_locks[DRV_EV_STATE_LOCK_CNT];
+int ERTS_WRITE_UNLIKELY(erts_no_pollsets) = 1;
+int ERTS_WRITE_UNLIKELY(erts_no_poll_threads) = 1;
+struct drv_ev_state_shared drv_ev_state;
 
-static ERTS_INLINE erts_mtx_t* fd_mtx(ErtsSysFdType fd)
-{
+static ERTS_INLINE int fd_hash(ErtsSysFdType fd) {
     int hash = (int)fd;
 # ifndef ERTS_SYS_CONTINOUS_FD_NUMBERS
     hash ^= (hash >> 9);
 # endif
-    return &drv_ev_state_locks[hash % DRV_EV_STATE_LOCK_CNT].lck;
+    return hash;
+}
+
+static ERTS_INLINE erts_mtx_t* fd_mtx(ErtsSysFdType fd)
+{
+    return &drv_ev_state.locks[fd_hash(fd) % ERTS_CHECK_IO_DRV_EV_STATE_LOCK_CNT].lck;
 }
 
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
 
-static erts_atomic_t drv_ev_state_len;
-static ErtsDrvEventState *drv_ev_state;
-static erts_mtx_t drv_ev_state_grow_lock; /* prevent lock-hogging of racing growers */
+static ERTS_INLINE ErtsDrvEventState *get_drv_ev_state(ErtsSysFdType fd)
+{
+    return &drv_ev_state.v[(int) fd];
+}
 
-#else
-static SafeHash drv_ev_state_tab;
-static int num_state_prealloc;
-static ErtsDrvEventState *state_prealloc_first;
-erts_spinlock_t state_prealloc_lock;
+#define new_drv_ev_state(State, fd) (State)
+#define erase_drv_ev_state(State)
+
+static ERTS_INLINE int grow_drv_ev_state(ErtsSysFdType fd) {
+    int i;
+    int old_len;
+    int new_len;
+
+    if ((unsigned)fd >= (unsigned)erts_atomic_read_nob(&drv_ev_state.len)) {
+
+	if (fd < 0 || fd >= drv_ev_state.max_fds)
+            return 0;
+
+        erts_mtx_lock(&drv_ev_state.grow_lock);
+        old_len = erts_atomic_read_nob(&drv_ev_state.len);
+        if (fd >= old_len) {
+            new_len = erts_poll_new_table_len(old_len, fd + 1);
+            if (new_len > drv_ev_state.max_fds)
+                new_len = drv_ev_state.max_fds;
+
+            for (i=0; i<ERTS_CHECK_IO_DRV_EV_STATE_LOCK_CNT; i++) { /* lock all fd's */
+                erts_mtx_lock(&drv_ev_state.locks[i].lck);
+            }
+            drv_ev_state.v = (drv_ev_state.v
+                              ? erts_realloc(ERTS_ALC_T_DRV_EV_STATE,
+                                             drv_ev_state.v,
+                                             sizeof(ErtsDrvEventState)*new_len)
+                              : erts_alloc(ERTS_ALC_T_DRV_EV_STATE,
+                                           sizeof(ErtsDrvEventState)*new_len));
+            ERTS_CT_ASSERT(ERTS_EV_TYPE_NONE == 0);
+            sys_memzero(drv_ev_state.v+old_len,
+                        sizeof(ErtsDrvEventState) * (new_len - old_len));
+            for (i = old_len; i < new_len; i++) {
+                drv_ev_state.v[i].fd = (ErtsSysFdType) i;
+            }
+            erts_atomic_set_nob(&drv_ev_state.len, new_len);
+            for (i=0; i<ERTS_CHECK_IO_DRV_EV_STATE_LOCK_CNT; i++) {
+                erts_mtx_unlock(&drv_ev_state.locks[i].lck);
+            }
+        }
+        /*else already grown by racing thread */
+
+        erts_mtx_unlock(&drv_ev_state.grow_lock);
+    }
+    return 1;
+}
 
-static ERTS_INLINE ErtsDrvEventState *hash_get_drv_ev_state(ErtsSysFdType fd)
+static int drv_ev_state_len(void)
+{
+    return erts_atomic_read_nob(&drv_ev_state.len);
+}
+
+#else /* !ERTS_SYS_CONTINOUS_FD_NUMBERS */
+
+static ERTS_INLINE ErtsDrvEventState *get_drv_ev_state(ErtsSysFdType fd)
 {
     ErtsDrvEventState tmpl;
     tmpl.fd = fd;
-    return  (ErtsDrvEventState *) safe_hash_get(&drv_ev_state_tab, (void *) &tmpl);
+    return  (ErtsDrvEventState *) safe_hash_get(&drv_ev_state.tab, (void *) &tmpl);
 }
 
-static ERTS_INLINE ErtsDrvEventState* hash_new_drv_ev_state(ErtsSysFdType fd)
+static ERTS_INLINE ErtsDrvEventState* new_drv_ev_state(ErtsDrvEventState *state,
+                                                       ErtsSysFdType fd)
 {
     ErtsDrvEventState tmpl;
+
+    if (state)
+        return state;
+
     tmpl.fd = fd;
     tmpl.driver.select = NULL;
-#if ERTS_CIO_HAVE_DRV_EVENT
-    tmpl.driver.event = NULL;
-#endif
     tmpl.driver.nif = NULL;
     tmpl.driver.stop.drv_ptr = NULL;
     tmpl.events = 0;
-    tmpl.remove_cnt = 0;
+    tmpl.active_events = 0;
     tmpl.type = ERTS_EV_TYPE_NONE;
     tmpl.flags = 0;
-    return  (ErtsDrvEventState *) safe_hash_put(&drv_ev_state_tab, (void *) &tmpl);
+
+    return  (ErtsDrvEventState *) safe_hash_put(&drv_ev_state.tab, (void *) &tmpl);
+}
+
+static ERTS_INLINE void erase_drv_ev_state(ErtsDrvEventState *state)
+{
+    safe_hash_erase(&drv_ev_state.tab, (void *) state);
 }
 
-static ERTS_INLINE void hash_erase_drv_ev_state(ErtsDrvEventState *state)
+static int drv_ev_state_len(void)
 {
-    ASSERT(state->remove_cnt == 0);
-    safe_hash_erase(&drv_ev_state_tab, (void *) state);
+    return erts_atomic_read_nob(&drv_ev_state.tab.nitems);
 }
 
 #endif /* !ERTS_SYS_CONTINOUS_FD_NUMBERS */
@@ -222,50 +288,47 @@ static void print_nif_select_op(erts_dsprintf_buf_t*, ErtsSysFdType,
 static void drv_select_large_fd_error(ErlDrvPort, ErtsSysFdType, int, int);
 static void nif_select_large_fd_error(ErtsSysFdType, int, ErtsResource*,Eterm ref);
 #endif
-#if ERTS_CIO_HAVE_DRV_EVENT
-static void drv_event_steal(ErlDrvPort ix, ErtsDrvEventState *state,
-			ErlDrvEventData event_data);
-static void print_drv_event_op(erts_dsprintf_buf_t *dsbufp,
-                               ErlDrvPort, ErtsSysFdType, ErlDrvEventData);
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-static void event_large_fd_error(ErlDrvPort, ErtsSysFdType, ErlDrvEventData);
-#endif
-#endif
 static void
 steal_pending_stop_use(erts_dsprintf_buf_t*, ErlDrvPort, ErtsDrvEventState*,
                        int mode, int on);
 static void
 steal_pending_stop_nif(erts_dsprintf_buf_t *dsbufp, ErtsResource*,
                        ErtsDrvEventState *state, int mode, int on);
-
-ERTS_SCHED_PREF_QUICK_ALLOC_IMPL(removed_fd, struct removed_fd, 64, ERTS_ALC_T_FD_LIST)
+static ERTS_INLINE void
+check_fd_cleanup(ErtsDrvEventState *state,
+		 ErtsDrvSelectDataState **free_select,
+                 ErtsNifSelectDataState **free_nif);
+static ERTS_INLINE void iready(Eterm id, ErtsDrvEventState *state);
+static ERTS_INLINE void oready(Eterm id, ErtsDrvEventState *state);
+#ifdef DEBUG_PRINT_MODE
+static char *drvmode2str(int mode);
+static char *nifmode2str(enum ErlNifSelectFlags mode);
+#endif
 
 static ERTS_INLINE void
-init_iotask(ErtsIoTask *io_task)
+init_iotask(ErtsIoTask *io_task, ErtsSysFdType fd)
 {
     erts_port_task_handle_init(&io_task->task);
-    erts_atomic_init_nob(&io_task->executed_time, ~((erts_aint_t) 0));
+    io_task->fd = fd;
 }
 
 static ERTS_INLINE int
-is_iotask_active(ErtsIoTask *io_task, erts_aint_t current_cio_time)
-{    
+is_iotask_active(ErtsIoTask *io_task)
+{
     if (erts_port_task_is_scheduled(&io_task->task))
 	return 1;
-    if (erts_atomic_read_nob(&io_task->executed_time) == current_cio_time)
-	return 1;
     return 0;
 }
 
 static ERTS_INLINE ErtsDrvSelectDataState *
-alloc_drv_select_data(void)
+alloc_drv_select_data(ErtsSysFdType fd)
 {
     ErtsDrvSelectDataState *dsp = erts_alloc(ERTS_ALC_T_DRV_SEL_D_STATE,
 					     sizeof(ErtsDrvSelectDataState));
     dsp->inport = NIL;
     dsp->outport = NIL;
-    init_iotask(&dsp->iniotask);
-    init_iotask(&dsp->outiotask);
+    init_iotask(&dsp->iniotask, fd);
+    init_iotask(&dsp->outiotask, fd);
     return dsp;
 }
 
@@ -276,8 +339,6 @@ alloc_nif_select_data(void)
 					     sizeof(ErtsNifSelectDataState));
     dsp->in.pid = NIL;
     dsp->out.pid = NIL;
-    dsp->in.ddeselect_cnt = 0;
-    dsp->out.ddeselect_cnt = 0;
     return dsp;
 }
 
@@ -295,201 +356,136 @@ free_nif_select_data(ErtsNifSelectDataState *dsp)
     erts_free(ERTS_ALC_T_NIF_SEL_D_STATE, dsp);
 }
 
-#if ERTS_CIO_HAVE_DRV_EVENT
-
-static ERTS_INLINE ErtsDrvEventDataState *
-alloc_drv_event_data(void)
+static ERTS_INLINE int
+get_pollset_id(ErtsSysFdType fd)
 {
-    ErtsDrvEventDataState *dep = erts_alloc(ERTS_ALC_T_DRV_EV_D_STATE,
-					    sizeof(ErtsDrvEventDataState));
-    dep->port = NIL;
-    dep->data = NULL;
-    dep->removed_events = 0;
-#if ERTS_CIO_DEFER_ACTIVE_EVENTS
-    dep->deferred_events = 0;
-#endif
-    init_iotask(&dep->iotask);
-    return dep;
+    return fd_hash(fd) % erts_no_pollsets;
 }
 
-static ERTS_INLINE void
-free_drv_event_data(ErtsDrvEventDataState *dep)
+static ERTS_INLINE ErtsPollSet *
+get_pollset(ErtsSysFdType fd)
 {
-    ASSERT(!erts_port_task_is_scheduled(&dep->iotask.task));
-    erts_free(ERTS_ALC_T_DRV_EV_D_STATE, dep);   
+    return pollsetv[get_pollset_id(fd)];
 }
 
-#endif /* ERTS_CIO_HAVE_DRV_EVENT */
+#if ERTS_POLL_USE_FALLBACK
+static ERTS_INLINE ErtsPollSet *
+get_fallback(void)
+{
+    return flbk_pollset;
+}
+#endif
 
-static ERTS_INLINE void
-remember_removed(ErtsDrvEventState *state, struct pollset_info* psi)
+/*
+ * Place a fd within a pollset. This will automatically use
+ * the fallback ps if needed.
+ */
+static ERTS_INLINE ErtsPollEvents
+erts_io_control_wakeup(ErtsDrvEventState *state, ErtsPollOp op,
+                       ErtsPollEvents pe, int *wake_poller)
 {
-    struct removed_fd *fdlp;
+    ErtsSysFdType fd = state->fd;
+    ErtsPollEvents res = 0;
+    EventStateFlags flags = state->flags;
+
     ERTS_LC_ASSERT(erts_lc_mtx_is_locked(fd_mtx(state->fd)));
-    if (erts_atomic_read_nob(&psi->in_poll_wait)) {
-	state->remove_cnt++;
-	ASSERT(state->remove_cnt > 0);
-	fdlp = removed_fd_alloc();
-    #if defined(ERTS_SYS_CONTINOUS_FD_NUMBERS) || defined(DEBUG)
-    	fdlp->fd = state->fd;
-    #endif
-    #ifndef ERTS_SYS_CONTINOUS_FD_NUMBERS
-	fdlp->state = state;
-    #endif
-	erts_spin_lock(&psi->removed_list_lock);
-	fdlp->next = psi->removed_list;
-	psi->removed_list = fdlp;
-	erts_spin_unlock(&psi->removed_list_lock);
+
+    if (!(flags & ERTS_EV_FLAG_FALLBACK)) {
+        res = erts_poll_control(get_pollset(fd), fd, op, pe, wake_poller);
+
+#if ERTS_POLL_USE_FALLBACK
+        if (op == ERTS_POLL_OP_ADD && res == ERTS_POLL_EV_NVAL) {
+            /* When an add fails with NVAL, the poll/kevent operation could not
+               put that fd in the pollset, so we instead put it into a fallback pollset */
+            state->flags |= ERTS_EV_FLAG_FALLBACK;
+            res = erts_poll_control_flbk(get_fallback(), fd, op, pe, wake_poller);
+        }
+    } else {
+        ASSERT(op != ERTS_POLL_OP_ADD);
+        res = erts_poll_control_flbk(get_fallback(), fd, op, pe, wake_poller);
+#endif
     }
-}
 
+    return res;
+}
 
-static ERTS_INLINE int
-is_removed(ErtsDrvEventState *state)
+static ERTS_INLINE ErtsPollEvents
+erts_io_control(ErtsDrvEventState *state, ErtsPollOp op, ErtsPollEvents pe)
 {
-    /* Note that there is a possible race here, where an fd is removed
-       (increasing remove_cnt) and then added again just before erts_poll_wait
-       is called by erts_check_io. Any polled event on the re-added fd will then
-       be falsely ignored. But that does not matter, as the event will trigger
-       again next time erl_check_io is called. */
-    return state->remove_cnt > 0;
+    int wake_poller = 0;
+    return erts_io_control_wakeup(state, op, pe, &wake_poller);
 }
 
-static void
-forget_removed(struct pollset_info* psi)
+/* ToDo: Was inline in erl_check_io.h but now need struct erts_poll_thread */
+void
+erts_io_notify_port_task_executed(ErtsPortTaskType type,
+                                  ErtsPortTaskHandle *pthp,
+                                  void (*reset_handle)(ErtsPortTaskHandle *))
 {
-    struct removed_fd* fdlp;
-    struct removed_fd* tofree;
+    ErtsIoTask *itp = ErtsContainerStruct(pthp, ErtsIoTask, task);
+    ErtsSysFdType fd = itp->fd;
+    erts_mtx_t *mtx = fd_mtx(fd);
+    int active_events;
+    ErtsDrvEventState *state;
+    ErtsDrvSelectDataState *free_select = NULL;
+    ErtsNifSelectDataState *free_nif = NULL;
 
-    /* Fast track: if (atomic_ptr(removed_list)==NULL) return; */
+    erts_mtx_lock(mtx);
+    state = get_drv_ev_state(fd);
 
-    erts_spin_lock(&psi->removed_list_lock);
-    fdlp = psi->removed_list;
-    psi->removed_list = NULL;
-    erts_spin_unlock(&psi->removed_list_lock);
+    active_events = state->active_events;
 
-    while (fdlp) {
-        ErtsResource* resource = NULL;
-	erts_driver_t* drv_ptr = NULL;
-	erts_mtx_t* mtx;
-	ErtsSysFdType fd;
-	ErtsDrvEventState *state;
+    switch (type) {
+    case ERTS_PORT_TASK_INPUT:
 
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-	fd = fdlp->fd;
-	mtx = fd_mtx(fd);
-	erts_mtx_lock(mtx);
-	state = &drv_ev_state[(int) fd];
-#else
-	state = fdlp->state;
-	fd = state->fd;
-	ASSERT(fd == fdlp->fd);
-	mtx = fd_mtx(fd);
-	erts_mtx_lock(mtx);
-#endif
-	ASSERT(state->remove_cnt > 0);
-	if (--state->remove_cnt == 0) {
-	    switch (state->type) {
-	    case ERTS_EV_TYPE_STOP_NIF:
-		/* Now we can call stop */
-		resource = state->driver.stop.resource;
-                state->driver.stop.resource = NULL;
-                ASSERT(resource);
-		state->type = ERTS_EV_TYPE_NONE;
-		state->flags &= ~ERTS_EV_FLAG_USED;
-                goto case_ERTS_EV_TYPE_NONE;
-
-	    case ERTS_EV_TYPE_STOP_USE:
-		/* Now we can call stop_select */
-		drv_ptr = state->driver.stop.drv_ptr;
-		ASSERT(drv_ptr);
-		state->type = ERTS_EV_TYPE_NONE;
-		state->flags &= ~ERTS_EV_FLAG_USED;
-		state->driver.stop.drv_ptr = NULL;
-		/* Fall through */
-            case ERTS_EV_TYPE_NONE:
-            case_ERTS_EV_TYPE_NONE:
-#ifndef ERTS_SYS_CONTINOUS_FD_NUMBERS
-		hash_erase_drv_ev_state(state);
-#endif
-		break;
-	    case ERTS_EV_TYPE_DRV_SEL:
-	    case ERTS_EV_TYPE_DRV_EV:
-		break;
-	    default:
-		ASSERT(0);
-	    }
-	}
-	erts_mtx_unlock(mtx);
-	if (drv_ptr) {
-	    int was_unmasked = erts_block_fpe();
-	    DTRACE1(driver_stop_select, drv_ptr->name);
-	    LTTNG1(driver_stop_select, drv_ptr->name);
-	    (*drv_ptr->stop_select) ((ErlDrvEvent) fd, NULL);
-	    erts_unblock_fpe(was_unmasked);
-	    if (drv_ptr->handle) {
-		erts_ddll_dereference_driver(drv_ptr->handle);
-	    }
-	}
-        if (resource) {
-            erts_resource_stop(resource, (ErlNifEvent)fd, 0);
-            enif_release_resource(resource->data);
-        }
+        DEBUG_PRINT_FD("executed ready_input", state);
+
+        ASSERT(!(state->active_events & ERTS_POLL_EV_IN));
+        if (state->events & ERTS_POLL_EV_IN)
+            active_events |= ERTS_POLL_EV_IN;
+        break;
+    case ERTS_PORT_TASK_OUTPUT:
 
-	tofree = fdlp;
-	fdlp = fdlp->next;
-	removed_fd_free(tofree);
+        DEBUG_PRINT_FD("executed ready_output", state);
+
+        ASSERT(!(state->active_events & ERTS_POLL_EV_OUT));
+        if (state->events & ERTS_POLL_EV_OUT)
+            active_events |= ERTS_POLL_EV_OUT;
+        break;
+    default:
+        erts_exit(ERTS_ABORT_EXIT, "Invalid IO port task type");
+        break;
     }
-}
 
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-static void
-grow_drv_ev_state(int min_ix)
-{
-    int i;
-    int old_len;
-    int new_len;
+    reset_handle(pthp);
 
-    erts_mtx_lock(&drv_ev_state_grow_lock);
-    old_len = erts_atomic_read_nob(&drv_ev_state_len);
-    if (min_ix >= old_len) {
-        new_len = erts_poll_new_table_len(old_len, min_ix + 1);
-        if (new_len > max_fds)
-            new_len = max_fds;
+    if (active_events) {
+        /* This is not needed if active_events has not changed */
+        if (state->active_events != active_events) {
+            ErtsPollEvents new_events;
+            state->active_events = active_events;
+            new_events = erts_io_control(state, ERTS_POLL_OP_MOD, active_events);
 
-	for (i=0; i<DRV_EV_STATE_LOCK_CNT; i++) { /* lock all fd's */
-	    erts_mtx_lock(&drv_ev_state_locks[i].lck);
-	}
-	drv_ev_state = (drv_ev_state
-			? erts_realloc(ERTS_ALC_T_DRV_EV_STATE,
-				       drv_ev_state,
-				       sizeof(ErtsDrvEventState)*new_len)
-			: erts_alloc(ERTS_ALC_T_DRV_EV_STATE,
-				     sizeof(ErtsDrvEventState)*new_len));
-	for (i = old_len; i < new_len; i++) {
-	    drv_ev_state[i].fd = (ErtsSysFdType) i;
-	    drv_ev_state[i].driver.select = NULL;
-#if ERTS_CIO_HAVE_DRV_EVENT
-	    drv_ev_state[i].driver.event = NULL;
-#endif
-	    drv_ev_state[i].driver.stop.drv_ptr = NULL;
-            drv_ev_state[i].driver.nif = NULL;
-	    drv_ev_state[i].events = 0;
-	    drv_ev_state[i].remove_cnt = 0;
-	    drv_ev_state[i].type = ERTS_EV_TYPE_NONE;
-	    drv_ev_state[i].flags = 0;
-	}
-	erts_atomic_set_nob(&drv_ev_state_len, new_len);
-	for (i=0; i<DRV_EV_STATE_LOCK_CNT; i++) {
-	    erts_mtx_unlock(&drv_ev_state_locks[i].lck);
-	}
+            /* We were unable to re-insert the fd into the pollset, signal the callback. */
+            if (new_events & (ERTS_POLL_EV_ERR|ERTS_POLL_EV_NVAL)) {
+                if (active_events & ERTS_POLL_EV_IN)
+                    iready(state->driver.select->inport, state);
+                if (active_events & ERTS_POLL_EV_OUT)
+                    oready(state->driver.select->outport, state);
+                state->active_events = 0;
+            }
+        }
+    } else {
+        check_fd_cleanup(state, &free_select, &free_nif);
     }
-    /*else already grown by racing thread */
 
-    erts_mtx_unlock(&drv_ev_state_grow_lock);
-}
-#endif /* ERTS_SYS_CONTINOUS_FD_NUMBERS */
+    erts_mtx_unlock(mtx);
 
+    if (free_select)
+        free_drv_select_data(free_select);
+    if (free_nif)
+        free_nif_select_data(free_nif);
+}
 
 static ERTS_INLINE void
 abort_task(Eterm id, ErtsPortTaskHandle *pthp, EventStateType type)
@@ -506,13 +502,6 @@ abort_tasks(ErtsDrvEventState *state, int mode)
     switch (mode) {
     case 0: check_type:
 	switch (state->type) {
-#if ERTS_CIO_HAVE_DRV_EVENT
-	case ERTS_EV_TYPE_DRV_EV:
-	    abort_task(state->driver.event->port,
-		       &state->driver.event->iotask.task,
-		       ERTS_EV_TYPE_DRV_EV);
-	    return;
-#endif
         case ERTS_EV_TYPE_NIF:
 	case ERTS_EV_TYPE_NONE:
 	    return;
@@ -542,16 +531,14 @@ abort_tasks(ErtsDrvEventState *state, int mode)
 static void
 deselect(ErtsDrvEventState *state, int mode)
 {
-    int do_wake = 0;
     ErtsPollEvents rm_events;
     ERTS_LC_ASSERT(erts_lc_mtx_is_locked(fd_mtx(state->fd)));
-    ASSERT(state->events);
 
     abort_tasks(state, mode);
 
-    if (!mode)
+    if (!mode) {
 	rm_events = state->events;
-    else {
+    } else {
 	rm_events = 0;
 	ASSERT(state->type == ERTS_EV_TYPE_DRV_SEL);
 	if (mode & ERL_DRV_READ) {
@@ -564,67 +551,63 @@ deselect(ErtsDrvEventState *state, int mode)
 	}
     }
 
-    state->events = ERTS_CIO_POLL_CTL(pollset.ps, state->fd, rm_events, 0, &do_wake);
+    state->events &= ~rm_events;
+    state->active_events &= ~rm_events;
 
     if (!(state->events)) {
+        erts_io_control(state, ERTS_POLL_OP_DEL, 0);
 	switch (state->type) {
         case ERTS_EV_TYPE_NIF:
             state->driver.nif->in.pid = NIL;
             state->driver.nif->out.pid = NIL;
-            state->driver.nif->in.ddeselect_cnt = 0;
-            state->driver.nif->out.ddeselect_cnt = 0;
-            enif_release_resource(state->driver.stop.resource);
+            enif_release_resource(state->driver.stop.resource->data);
             state->driver.stop.resource = NULL;
             break;
 	case ERTS_EV_TYPE_DRV_SEL:
 	    state->driver.select->inport = NIL;
 	    state->driver.select->outport = NIL;
 	    break;
-#if ERTS_CIO_HAVE_DRV_EVENT
-	case ERTS_EV_TYPE_DRV_EV:
-	    state->driver.event->port = NIL;
-	    state->driver.event->data = NULL;
-	    state->driver.event->removed_events = (ErtsPollEvents) 0;
-	    break;
-#endif
 	case ERTS_EV_TYPE_NONE:
 	    break;
 	default:
 	    ASSERT(0);
 	    break;
 	}
-	    
 	state->type = ERTS_EV_TYPE_NONE;
-	state->flags &= ~ERTS_EV_FLAG_USED;
-	remember_removed(state, &pollset);
+	state->flags = 0;
+    } else {
+        ErtsPollEvents new_events =
+            erts_io_control(state, ERTS_POLL_OP_MOD, state->active_events);
+
+        /* We were unable to re-insert the fd into the pollset, signal the callback. */
+        if (new_events & (ERTS_POLL_EV_ERR|ERTS_POLL_EV_NVAL)) {
+            if (state->active_events & ERTS_POLL_EV_IN)
+                iready(state->driver.select->inport, state);
+            if (state->active_events & ERTS_POLL_EV_OUT)
+                oready(state->driver.select->outport, state);
+            state->active_events = 0;
+        }
     }
 }
 
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-#  define IS_FD_UNKNOWN(state) ((state)->type == ERTS_EV_TYPE_NONE && (state)->remove_cnt == 0)
+#  define IS_FD_UNKNOWN(state) ((state)->type == ERTS_EV_TYPE_NONE)
 #else
 #  define IS_FD_UNKNOWN(state) ((state) == NULL)
 #endif
 
 static ERTS_INLINE void
 check_fd_cleanup(ErtsDrvEventState *state,
-#if ERTS_CIO_HAVE_DRV_EVENT
-		 ErtsDrvEventDataState **free_event,
-#endif
 		 ErtsDrvSelectDataState **free_select,
                  ErtsNifSelectDataState **free_nif)
 {
-    erts_aint_t current_cio_time;
-
     ERTS_LC_ASSERT(erts_lc_mtx_is_locked(fd_mtx(state->fd)));
-
-    current_cio_time = erts_atomic_read_acqb(&erts_check_io_time);
     *free_select = NULL;
     if (state->driver.select
 	&& (state->type != ERTS_EV_TYPE_DRV_SEL)
-	&& !is_iotask_active(&state->driver.select->iniotask, current_cio_time)
-	&& !is_iotask_active(&state->driver.select->outiotask, current_cio_time)) {
-	
+	&& !is_iotask_active(&state->driver.select->iniotask)
+	&& !is_iotask_active(&state->driver.select->outiotask)) {
+
 	*free_select = state->driver.select;
 	state->driver.select = NULL;
     }
@@ -635,382 +618,85 @@ check_fd_cleanup(ErtsDrvEventState *state,
         state->driver.nif = NULL;
     }
 
-#if ERTS_CIO_HAVE_DRV_EVENT
-    *free_event = NULL;
-    if (state->driver.event
-	&& (state->type != ERTS_EV_TYPE_DRV_EV)
-	&& !is_iotask_active(&state->driver.event->iotask,  current_cio_time)) {
-	
-	*free_event = state->driver.event;
-	state->driver.event = NULL;
-    }
-#endif
-
-#ifndef ERTS_SYS_CONTINOUS_FD_NUMBERS
     if (((state->type != ERTS_EV_TYPE_NONE)
-	 | state->remove_cnt
-#if ERTS_CIO_HAVE_DRV_EVENT
-	 | (state->driver.event != NULL)
-#endif
+         | (state->driver.nif != NULL)
 	 | (state->driver.select != NULL)) == 0) {
 
-	hash_erase_drv_ev_state(state);
-
+	erase_drv_ev_state(state);
     }
-#endif
 }
 
-static ERTS_INLINE int
-check_cleanup_active_fd(ErtsSysFdType fd,
-#if ERTS_CIO_DEFER_ACTIVE_EVENTS
-			ErtsPollControlEntry *pce,
-			int *pce_ix,
-#endif
-			erts_aint_t current_cio_time,
-                        int may_sleep)
-{
-    ErtsDrvEventState *state;
-    int active = 0;
-    erts_mtx_t *mtx = fd_mtx(fd);
-    void *free_select = NULL;
-    void *free_nif = NULL;
-#if ERTS_CIO_HAVE_DRV_EVENT
-    void *free_event = NULL;
-#endif
-#if ERTS_CIO_DEFER_ACTIVE_EVENTS
-    ErtsPollEvents evon = 0, evoff = 0;
-#endif
-
-    erts_mtx_lock(mtx);
-
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    state = &drv_ev_state[(int) fd];
+#ifdef __WIN32__
+# define MUST_DEFER(MAY_SLEEP) 1
 #else
-    state = hash_get_drv_ev_state(fd); /* may be NULL! */
-    if (state)
-#endif
-    {
-	if (state->driver.select) {
-#if ERTS_CIO_DEFER_ACTIVE_EVENTS
-	    if (is_iotask_active(&state->driver.select->iniotask, current_cio_time)) {
-		active = 1;
-		if ((state->events & ERTS_POLL_EV_IN)
-		    && !(state->flags & ERTS_EV_FLAG_DEFER_IN_EV)) {
-		    evoff |= ERTS_POLL_EV_IN;
-		    state->flags |= ERTS_EV_FLAG_DEFER_IN_EV;
-		}
-	    }
-	    else if (state->flags & ERTS_EV_FLAG_DEFER_IN_EV) {
-		if (state->events & ERTS_POLL_EV_IN)
-		    evon |= ERTS_POLL_EV_IN;
-		state->flags &= ~ERTS_EV_FLAG_DEFER_IN_EV;
-	    }
-	    if (is_iotask_active(&state->driver.select->outiotask, current_cio_time)) {
-		active = 1;
-		if ((state->events & ERTS_POLL_EV_OUT)
-		    && !(state->flags & ERTS_EV_FLAG_DEFER_OUT_EV)) {
-		    evoff |= ERTS_POLL_EV_OUT;
-		    state->flags |= ERTS_EV_FLAG_DEFER_OUT_EV;
-		}
-	    }
-	    else if (state->flags & ERTS_EV_FLAG_DEFER_OUT_EV) {
-		if (state->events & ERTS_POLL_EV_OUT)
-		    evon |= ERTS_POLL_EV_OUT;
-		state->flags &= ~ERTS_EV_FLAG_DEFER_OUT_EV;
-	    }
-	    if (active)
-		(void) 0;
-	    else
-#else
-	    if (is_iotask_active(&state->driver.select->iniotask, current_cio_time)
-		|| is_iotask_active(&state->driver.select->outiotask, current_cio_time))
-		active = 1;
-	    else
-#endif
-		if (state->type != ERTS_EV_TYPE_DRV_SEL) {
-		free_select = state->driver.select;
-		state->driver.select = NULL;
-	    }
-	}
-
-        if (state->driver.nif) {
-            ErtsPollEvents rm_events = 0;
-            if (state->driver.nif->in.ddeselect_cnt) {
-                ASSERT(state->type == ERTS_EV_TYPE_NIF);
-                ASSERT(state->events & ERTS_POLL_EV_IN);
-                ASSERT(is_nil(state->driver.nif->in.pid));
-                if (may_sleep || state->driver.nif->in.ddeselect_cnt == 1) {
-                    rm_events = ERTS_POLL_EV_IN;
-                    state->driver.nif->in.ddeselect_cnt = 0;
-                }
-            }
-            if (state->driver.nif->out.ddeselect_cnt) {
-                ASSERT(state->type == ERTS_EV_TYPE_NIF);
-                ASSERT(state->events & ERTS_POLL_EV_OUT);
-                ASSERT(is_nil(state->driver.nif->out.pid));
-                if (may_sleep || state->driver.nif->out.ddeselect_cnt == 1) {
-                    rm_events |= ERTS_POLL_EV_OUT;
-                    state->driver.nif->out.ddeselect_cnt = 0;
-                }
-            }
-            if (rm_events) {
-                int do_wake = 0;
-                state->events = ERTS_CIO_POLL_CTL(pollset.ps, state->fd,
-                                                  rm_events, 0, &do_wake);
-            }
-            if (state->events)
-                active = 1;
-            else if (state->type != ERTS_EV_TYPE_NIF) {
-                free_nif = state->driver.nif;
-                state->driver.nif = NULL;
-            }
-        }
-
-#if ERTS_CIO_HAVE_DRV_EVENT
-	if (state->driver.event) {
-	    if (is_iotask_active(&state->driver.event->iotask, current_cio_time)) {
-#if ERTS_CIO_DEFER_ACTIVE_EVENTS
-		ErtsPollEvents evs = state->events & ~state->driver.event->deferred_events;
-		if (evs) {
-		    evoff |= evs;
-		    state->driver.event->deferred_events |= evs;
-		}
-#endif
-		active = 1;
-	    }
-	    else if (state->type != ERTS_EV_TYPE_DRV_EV) {
-		free_event = state->driver.event;
-		state->driver.event = NULL;
-	    }
-#if ERTS_CIO_DEFER_ACTIVE_EVENTS
-	    else {
-		ErtsPollEvents evs = state->events & state->driver.event->deferred_events;
-		if (evs) {
-		    evon |= evs;
-		    state->driver.event->deferred_events = 0;
-		}
-	    }
-#endif
-
-	}
-#endif
-
-#ifndef ERTS_SYS_CONTINOUS_FD_NUMBERS
-	if (((state->type != ERTS_EV_TYPE_NONE) | state->remove_cnt | active) == 0)
-	    hash_erase_drv_ev_state(state);
-#endif
-
-    }
-
-    erts_mtx_unlock(mtx);
-
-    if (free_select)
-	free_drv_select_data(free_select);
-    if (free_nif)
-        free_nif_select_data(free_nif);
-#if ERTS_CIO_HAVE_DRV_EVENT
-    if (free_event)
-	free_drv_event_data(free_event);
+# define MUST_DEFER(MAY_SLEEP) (MAY_SLEEP)
 #endif
 
-#if ERTS_CIO_DEFER_ACTIVE_EVENTS
-    if (evoff) {
-	ErtsPollControlEntry *pcep = &pce[(*pce_ix)++];
-	pcep->fd = fd;
-	pcep->events = evoff;
-	pcep->on = 0;
-    }
-    if (evon) {
-	ErtsPollControlEntry *pcep = &pce[(*pce_ix)++];
-	pcep->fd = fd;
-	pcep->events = evon;
-	pcep->on = 1;
-    }
-#endif
-
-    return active;
-}
-
-static void
-check_cleanup_active_fds(erts_aint_t current_cio_time, int may_sleep)
-{
-    int six = pollset.active_fd.six;
-    int eix = pollset.active_fd.eix;
-    erts_aint32_t no = erts_atomic32_read_dirty(&pollset.active_fd.no);
-    int size = pollset.active_fd.size;
-    int ix = six;
-#if ERTS_CIO_DEFER_ACTIVE_EVENTS
-    /* every fd might add two entries */
-    Uint pce_sz = 2*sizeof(ErtsPollControlEntry)*no;
-    ErtsPollControlEntry *pctrl_entries = (pce_sz
-					   ? erts_alloc(ERTS_ALC_T_TMP, pce_sz)
-					   : NULL);
-    int pctrl_ix = 0;
-#endif
-
-    while (ix != eix) {
-	ErtsSysFdType fd = pollset.active_fd.array[ix];
-	int nix = ix + 1;
-	if (nix >= size)
-	    nix = 0;
-	ASSERT(fd != ERTS_SYS_FD_INVALID);
-	if (!check_cleanup_active_fd(fd,
-#if ERTS_CIO_DEFER_ACTIVE_EVENTS
-				     pctrl_entries,
-				     &pctrl_ix,
-#endif
-				     current_cio_time,
-                                     may_sleep)) {
-	    no--;
-	    if (ix == six) {
-#ifdef DEBUG
-		pollset.active_fd.array[ix] = ERTS_SYS_FD_INVALID;
-#endif
-		six = nix;
-	    }
-	    else {
-		pollset.active_fd.array[ix] = pollset.active_fd.array[six];
-#ifdef DEBUG
-		pollset.active_fd.array[six] = ERTS_SYS_FD_INVALID;
-#endif
-		six++;
-		if (six >= size)
-		    six = 0;
-	    }
-	}
-	ix = nix;
-    }
-
-#if ERTS_CIO_DEFER_ACTIVE_EVENTS
-    ASSERT(pctrl_ix <= pce_sz/sizeof(ErtsPollControlEntry));
-    if (pctrl_ix)
-	ERTS_CIO_POLL_CTLV(pollset.ps, pctrl_entries, pctrl_ix);
-    if (pctrl_entries)
-	erts_free(ERTS_ALC_T_TMP, pctrl_entries);
-#endif
-
-    pollset.active_fd.six = six;
-    pollset.active_fd.eix = eix;
-    erts_atomic32_set_relb(&pollset.active_fd.no, no);
-}
-
-static void grow_active_fds(void)
-{
-    ASSERT(pollset.active_fd.six == pollset.active_fd.eix);
-    pollset.active_fd.six = 0;
-    pollset.active_fd.eix = pollset.active_fd.size;
-    pollset.active_fd.size += ERTS_ACTIVE_FD_INC;
-    pollset.active_fd.array = erts_realloc(ERTS_ALC_T_ACTIVE_FD_ARR,
-                                           pollset.active_fd.array,
-                                           pollset.active_fd.size*sizeof(ErtsSysFdType));
-#ifdef DEBUG
-    {
-        int i;
-        for (i = pollset.active_fd.eix + 1; i < pollset.active_fd.size; i++)
-            pollset.active_fd.array[i] = ERTS_SYS_FD_INVALID;
-    }
-#endif
-}
-
-static ERTS_INLINE void
-add_active_fd(ErtsSysFdType fd)
-{
-    int eix = pollset.active_fd.eix;
-    int size = pollset.active_fd.size;
-    
-    pollset.active_fd.array[eix] = fd;
-
-    erts_atomic32_set_relb(&pollset.active_fd.no,
-			       (erts_atomic32_read_dirty(&pollset.active_fd.no)
-				+ 1));
-
-    eix++;
-    if (eix >= size)
-	eix = 0;
-    pollset.active_fd.eix = eix;
-
-    if (pollset.active_fd.six == eix) {
-        grow_active_fds();
-    }
-}
-
 int
-ERTS_CIO_EXPORT(driver_select)(ErlDrvPort ix,
-			       ErlDrvEvent e,
-			       int mode,
-			       int on)
+driver_select(ErlDrvPort ix, ErlDrvEvent e, int mode, int on)
 {
     void (*stop_select_fn)(ErlDrvEvent, void*) = NULL;
     Port *prt = erts_drvport2port(ix);
     Eterm id = erts_drvport2id(ix);
     ErtsSysFdType fd = (ErtsSysFdType) e;
     ErtsPollEvents ctl_events = (ErtsPollEvents) 0;
-    ErtsPollEvents new_events, old_events;
+    ErtsPollEvents old_events;
+    ErtsPollEvents new_events;
+    ErtsPollOp ctl_op = ERTS_POLL_OP_MOD;
     ErtsDrvEventState *state;
-    int wake_poller;
+    int wake_poller = 0;
     int ret;
-#if ERTS_CIO_HAVE_DRV_EVENT
-    ErtsDrvEventDataState *free_event = NULL;
-#endif
     ErtsDrvSelectDataState *free_select = NULL;
     ErtsNifSelectDataState *free_nif = NULL;
 #ifdef USE_VM_PROBES
     DTRACE_CHARBUF(name, 64);
 #endif
+    ERTS_MSACC_PUSH_AND_SET_STATE(ERTS_MSACC_STATE_CHECK_IO);
 
-    if (prt == ERTS_INVALID_ERL_DRV_PORT)
+    if (prt == ERTS_INVALID_ERL_DRV_PORT) {
+        ERTS_MSACC_POP_STATE();
 	return -1;
+    }
 
     ERTS_LC_ASSERT(erts_lc_is_port_locked(prt));
 
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    if ((unsigned)fd >= (unsigned)erts_atomic_read_nob(&drv_ev_state_len)) {
-	if (fd < 0) {
-	    return -1;    
-	}
-	if (fd >= max_fds) {
-	    drv_select_large_fd_error(ix, fd, mode, on);
-	    return -1;
-	}
-	grow_drv_ev_state(fd);
+    if (!grow_drv_ev_state(fd)) {
+        if (fd > 0) drv_select_large_fd_error(ix, fd, mode, on);
+        ERTS_MSACC_POP_STATE();
+        return -1;
     }
 #endif
 
     erts_mtx_lock(fd_mtx(fd));
 
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    state = &drv_ev_state[(int) fd];
-#else
-    state = hash_get_drv_ev_state(fd); /* may be NULL! */
-#endif
+    state = get_drv_ev_state(fd); /* may be NULL! */
 
-    if (!on && (mode&ERL_DRV_USE_NO_CALLBACK) == ERL_DRV_USE) {
-	if (IS_FD_UNKNOWN(state)) {
-	    /* fast track to stop_select callback */
-	    stop_select_fn = prt->drv_ptr->stop_select;
-#ifdef USE_VM_PROBES
-	    strncpy(name, prt->drv_ptr->name,
-		    sizeof(DTRACE_CHARBUF_NAME(name))-1);
-	    name[sizeof(name)-1] = '\0';
-#endif
-	    ret = 0;
-	    goto done_unknown;
-	}
-	mode |= (ERL_DRV_READ | ERL_DRV_WRITE);
-	wake_poller = 1; /* to eject fd from pollset (if needed) */
-    }
-    else wake_poller = 0;
+    DEBUG_PRINT_FD("driver_select(%T, %p, %s, %d)",
+                   state, id, fd, drvmode2str(mode), on);
 
-#ifndef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    if (state == NULL) {
-	state = hash_new_drv_ev_state(fd);
+    if (!on) {
+        if (IS_FD_UNKNOWN(state)) {
+            if ((mode&ERL_DRV_USE_NO_CALLBACK) == ERL_DRV_USE) {
+                /* fast track to stop_select callback */
+                stop_select_fn = prt->drv_ptr->stop_select;
+        #ifdef USE_VM_PROBES
+                strncpy(name, prt->drv_ptr->name,
+                        sizeof(DTRACE_CHARBUF_NAME(name))-1);
+                name[sizeof(name)-1] = '\0';
+        #endif
+            }
+            ret = 0;
+            goto done_unknown;
+        }
+        else if ((mode&ERL_DRV_USE_NO_CALLBACK) == ERL_DRV_USE) {
+            mode |= (ERL_DRV_READ | ERL_DRV_WRITE);
+        }
     }
-#endif
+
+    state = new_drv_ev_state(state, fd);
 
     switch (state->type) {
-#if ERTS_CIO_HAVE_DRV_EVENT
-    case ERTS_EV_TYPE_DRV_EV:
-#endif
     case ERTS_EV_TYPE_NIF:
         drv_select_steal(ix, state, mode, on);
         break;
@@ -1032,7 +718,9 @@ ERTS_CIO_EXPORT(driver_select)(ErlDrvPort ix,
         ASSERT(state->type == ERTS_EV_TYPE_NONE);
         break;
 
-    }}
+    }
+    default: break;
+    }
 
     if (mode & ERL_DRV_READ) {
 	if (state->type == ERTS_EV_TYPE_DRV_SEL) {
@@ -1040,7 +728,7 @@ ERTS_CIO_EXPORT(driver_select)(ErlDrvPort ix,
 	    if (owner != id && is_not_nil(owner))
 		drv_select_steal(ix, state, mode, on);
 	}
-	ctl_events |= ERTS_POLL_EV_IN;
+        ctl_events = ERTS_POLL_EV_IN;
     }
     if (mode & ERL_DRV_WRITE) {
 	if (state->type == ERTS_EV_TYPE_DRV_SEL) {
@@ -1049,100 +737,105 @@ ERTS_CIO_EXPORT(driver_select)(ErlDrvPort ix,
 		drv_select_steal(ix, state, mode, on);
 	}
 	ctl_events |= ERTS_POLL_EV_OUT;
-    }	
+    }
+
 
     ASSERT((state->type == ERTS_EV_TYPE_DRV_SEL) ||
 	   (state->type == ERTS_EV_TYPE_NONE && !state->events));
 
-    if (!on && !(state->flags & ERTS_EV_FLAG_USED) 
-	&& state->events && !(state->events & ~ctl_events)) {	
-	/* Old driver removing all events. At least wake poller.
-	   It will not make close() 100% safe but it will prevent
-	   actions delayed by poll timeout. */
-	wake_poller = 1;
-    }
+    old_events = state->events;
 
-    new_events = ERTS_CIO_POLL_CTL(pollset.ps, state->fd, ctl_events, on, &wake_poller);
+    if (on) {
+        ctl_events &= ~old_events;
+        state->events |= ctl_events;
+        if (ctl_events & ERTS_POLL_EV_IN && (!state->driver.select || !is_iotask_active(&state->driver.select->iniotask)))
+            state->active_events |= ERTS_POLL_EV_IN;
+        if (ctl_events & ERTS_POLL_EV_OUT && (!state->driver.select || !is_iotask_active(&state->driver.select->outiotask)))
+            state->active_events |= ERTS_POLL_EV_OUT;
+        if (old_events == 0 && !(state->flags & ERTS_EV_FLAG_USED)) {
+            ctl_op = ERTS_POLL_OP_ADD;
+        }
+    }
+    else {
+        ctl_events &= old_events;
+        state->events &= ~ctl_events;
+        state->active_events &= ~ctl_events;
 
-    if (new_events & (ERTS_POLL_EV_ERR|ERTS_POLL_EV_NVAL)) {
-	if (state->type == ERTS_EV_TYPE_DRV_SEL && !state->events) {
-	    state->type = ERTS_EV_TYPE_NONE;
-	    state->flags &= ~ERTS_EV_FLAG_USED;
-	    state->driver.select->inport = NIL;
-	    state->driver.select->outport = NIL;
-	}
-	ret = -1;
-	goto done;
+        if (!state->events) {
+            if (!(state->flags & ERTS_EV_FLAG_USED) || mode & ERL_DRV_USE)
+                ctl_op = ERTS_POLL_OP_DEL;
+        }
     }
 
-    old_events = state->events;
+    if (ctl_events || ctl_op == ERTS_POLL_OP_DEL) {
 
-    ASSERT(on
-	   ? (new_events == (state->events | ctl_events))
-	   : (new_events == (state->events & ~ctl_events)));
+        new_events = erts_io_control_wakeup(state, ctl_op,
+                                            state->active_events,
+                                            &wake_poller);
 
-    ASSERT(state->type == ERTS_EV_TYPE_DRV_SEL
-	   || state->type == ERTS_EV_TYPE_NONE);
+        ASSERT(state->type == ERTS_EV_TYPE_DRV_SEL || state->type == ERTS_EV_TYPE_NONE);
+    }
 
-    state->events = new_events;
-    if (ctl_events) {
-	if (on) {
+    if (on) {
+        if (ctl_events) {
 	    if (!state->driver.select)
-		state->driver.select = alloc_drv_select_data();
+		state->driver.select = alloc_drv_select_data(state->fd);
 	    if (state->type == ERTS_EV_TYPE_NONE)
 		state->type = ERTS_EV_TYPE_DRV_SEL;
 	    ASSERT(state->type == ERTS_EV_TYPE_DRV_SEL);
-	    if (ctl_events & ERTS_POLL_EV_IN)
+	    if (ctl_events & ERTS_POLL_EV_IN) {
 		state->driver.select->inport = id;
-	    if (ctl_events & ERTS_POLL_EV_OUT)
+                if (new_events & (ERTS_POLL_EV_ERR|ERTS_POLL_EV_NVAL))
+                    iready(id, state);
+            }
+	    if (ctl_events & ERTS_POLL_EV_OUT) {
 		state->driver.select->outport = id;
-	    if (mode & ERL_DRV_USE) {
+                if (new_events & (ERTS_POLL_EV_ERR|ERTS_POLL_EV_NVAL))
+                    oready(id, state);
+            }
+	    if (mode & ERL_DRV_USE)
 		state->flags |= ERTS_EV_FLAG_USED;
-	    }
-	}
-	else { /* off */
-	    if (state->type == ERTS_EV_TYPE_DRV_SEL) {
-		if (ctl_events & ERTS_POLL_EV_IN) {
-		    abort_tasks(state, ERL_DRV_READ);
-		    state->driver.select->inport = NIL;
-		}
-		if (ctl_events & ERTS_POLL_EV_OUT) {
-		    abort_tasks(state, ERL_DRV_WRITE);
-		    state->driver.select->outport = NIL;
-		}
-		if (new_events == 0) {
-		    if (old_events != 0) {
-			remember_removed(state, &pollset);
-		    }		    
-		    if ((mode & ERL_DRV_USE) || !(state->flags & ERTS_EV_FLAG_USED)) {
-			state->type = ERTS_EV_TYPE_NONE;
-			state->flags &= ~ERTS_EV_FLAG_USED;
-		    }
-		    /*else keep it, as fd will probably be selected upon again */
-		}
-	    }
-	    if ((mode & ERL_DRV_USE_NO_CALLBACK) == ERL_DRV_USE) {
-		erts_driver_t* drv_ptr = prt->drv_ptr;
-		ASSERT(new_events==0);
-		if (state->remove_cnt == 0 || !wake_poller) {
-		    /* Safe to close fd now as it is not in pollset
-		       or there was no need to eject fd (kernel poll) */
-		    stop_select_fn = drv_ptr->stop_select;
+        }
+    }
+    else { /* off */
+        if (state->type == ERTS_EV_TYPE_DRV_SEL) {
+            if (ctl_events & ERTS_POLL_EV_IN) {
+                abort_tasks(state, ERL_DRV_READ);
+                state->driver.select->inport = NIL;
+            }
+            if (ctl_events & ERTS_POLL_EV_OUT) {
+                abort_tasks(state, ERL_DRV_WRITE);
+                state->driver.select->outport = NIL;
+            }
+            if (state->events == 0) {
+                if ((mode & ERL_DRV_USE) || !(state->flags & ERTS_EV_FLAG_USED)) {
+                    state->type = ERTS_EV_TYPE_NONE;
+                    state->flags = 0;
+                }
+                /*else keep it, as fd will probably be selected upon again */
+            }
+        }
+        if ((mode & ERL_DRV_USE_NO_CALLBACK) == ERL_DRV_USE) {
+            erts_driver_t* drv_ptr = prt->drv_ptr;
+            ASSERT(state->events==0);
+            if (!wake_poller) {
+                /* Safe to close fd now as it is not in pollset
+                   or there was no need to eject fd (kernel poll) */
+                stop_select_fn = drv_ptr->stop_select;
 #ifdef USE_VM_PROBES
-		    strncpy(name, prt->drv_ptr->name, sizeof(name)-1);
-		    name[sizeof(name)-1] = '\0';
+                strncpy(name, prt->drv_ptr->name, sizeof(name)-1);
+                name[sizeof(name)-1] = '\0';
 #endif
-		}
-		else {
-		    /* Not safe to close fd, postpone stop_select callback. */
-		    state->type = ERTS_EV_TYPE_STOP_USE;
-		    state->driver.stop.drv_ptr = drv_ptr;
-		    if (drv_ptr->handle) {
-			erts_ddll_reference_referenced_driver(drv_ptr->handle);
-		    }
-		}
-	    }
-	}
+            }
+            else {
+                /* Not safe to close fd, postpone stop_select callback. */
+                state->type = ERTS_EV_TYPE_STOP_USE;
+                state->driver.stop.drv_ptr = drv_ptr;
+                if (drv_ptr->handle) {
+                    erts_ddll_reference_referenced_driver(drv_ptr->handle);
+                }
+            }
+        }
     }
    
     ret = 0;
@@ -1150,9 +843,6 @@ ERTS_CIO_EXPORT(driver_select)(ErlDrvPort ix,
 done:
 
     check_fd_cleanup(state,
-#if ERTS_CIO_HAVE_DRV_EVENT
-		     &free_event,
-#endif
 		     &free_select,
                      &free_nif);
 
@@ -1170,61 +860,47 @@ done_unknown:
     if (free_nif)
         free_nif_select_data(free_nif);
 
-#if ERTS_CIO_HAVE_DRV_EVENT
-    if (free_event)
-	free_drv_event_data(free_event);
-#endif
+    ERTS_MSACC_POP_STATE();
+
     return ret;
 }
 
 int
-ERTS_CIO_EXPORT(enif_select)(ErlNifEnv* env,
-                             ErlNifEvent e,
-                             enum ErlNifSelectFlags mode,
-                             void* obj,
-                             const ErlNifPid* pid,
-                             Eterm ref)
+enif_select(ErlNifEnv* env,
+            ErlNifEvent e,
+            enum ErlNifSelectFlags mode,
+            void* obj,
+            const ErlNifPid* pid,
+            Eterm ref)
 {
     int on;
     ErtsResource* resource = DATA_TO_RESOURCE(obj);
     ErtsSysFdType fd = (ErtsSysFdType) e;
     ErtsPollEvents ctl_events = (ErtsPollEvents) 0;
-    ErtsPollEvents new_events, old_events;
+    ErtsPollEvents old_events;
+    ErtsPollOp ctl_op = ERTS_POLL_OP_MOD;
     ErtsDrvEventState *state;
-    int wake_poller;
-    int ret;
+    int ret, wake_poller = 0;
     enum { NO_STOP=0, CALL_STOP, CALL_STOP_AND_RELEASE } call_stop = NO_STOP;
-#if ERTS_CIO_HAVE_DRV_EVENT
-    ErtsDrvEventDataState *free_event = NULL;
-#endif
     ErtsDrvSelectDataState *free_select = NULL;
     ErtsNifSelectDataState *free_nif = NULL;
-#ifdef USE_VM_PROBES
-    DTRACE_CHARBUF(name, 64);
-#endif
 
     ASSERT(!(resource->monitors && resource->monitors->is_dying));
 
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    if ((unsigned)fd >= (unsigned)erts_atomic_read_nob(&drv_ev_state_len)) {
-	if (fd < 0) {
-	    return INT_MIN | ERL_NIF_SELECT_INVALID_EVENT;
-	}
-	if (fd >= max_fds) {
-	    nif_select_large_fd_error(fd, mode, resource, ref);
-            return INT_MIN | ERL_NIF_SELECT_INVALID_EVENT;
-	}
-	grow_drv_ev_state(fd);
+    if (!grow_drv_ev_state(fd)) {
+        if (fd > 0) nif_select_large_fd_error(fd, mode, resource, ref);
+        return INT_MIN | ERL_NIF_SELECT_INVALID_EVENT;
     }
 #endif
 
     erts_mtx_lock(fd_mtx(fd));
 
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    state = &drv_ev_state[(int) fd];
-#else
-    state = hash_get_drv_ev_state(fd); /* may be NULL! */
-#endif
+    state = get_drv_ev_state(fd); /* may be NULL! */
+
+    DEBUG_PRINT_FD("enif_select(%T, %d, %s, %p, %T, %T)",
+                   state, env->proc->common.id, fd, nifmode2str(mode), resource,
+                   pid ? pid->pid : THE_NON_VALUE, ref);
 
     if (mode & ERL_NIF_SELECT_STOP) {
         ASSERT(resource->type->stop);
@@ -1236,13 +912,12 @@ ERTS_CIO_EXPORT(enif_select)(ErlNifEnv* env,
         }
         on = 0;
         mode = ERL_DRV_READ | ERL_DRV_WRITE | ERL_DRV_USE;
-        wake_poller = 1; /* to eject fd from pollset (if needed) */
         ctl_events = ERTS_POLL_EV_IN | ERTS_POLL_EV_OUT;
+        ctl_op = ERTS_POLL_OP_DEL;
     }
     else {
         on = 1;
         ASSERT(mode);
-        wake_poller = 0;
         if (mode & ERL_DRV_READ) {
             ctl_events |= ERTS_POLL_EV_IN;
         }
@@ -1251,11 +926,7 @@ ERTS_CIO_EXPORT(enif_select)(ErlNifEnv* env,
         }
     }
 
-#ifndef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    if (state == NULL) {
-	state = hash_new_drv_ev_state(fd);
-    }
-#endif
+    state = new_drv_ev_state(state,fd);
 
     switch (state->type) {
     case ERTS_EV_TYPE_NIF:
@@ -1266,9 +937,6 @@ ERTS_CIO_EXPORT(enif_select)(ErlNifEnv* env,
         if (state->driver.stop.resource != resource)
             nif_select_steal(state, ERL_DRV_READ | ERL_DRV_WRITE, resource, ref);
         break;
-#if ERTS_CIO_HAVE_DRV_EVENT
-    case ERTS_EV_TYPE_DRV_EV:
-#endif
     case ERTS_EV_TYPE_DRV_SEL:
         nif_select_steal(state, mode, resource, ref);
         break;
@@ -1289,37 +957,52 @@ ERTS_CIO_EXPORT(enif_select)(ErlNifEnv* env,
         }
         ASSERT(state->type == ERTS_EV_TYPE_NONE);
         break;
-    }}
+    }
+    default: break;
+    }
 
     ASSERT((state->type == ERTS_EV_TYPE_NIF) ||
 	   (state->type == ERTS_EV_TYPE_NONE && !state->events));
 
-    new_events = ERTS_CIO_POLL_CTL(pollset.ps, state->fd, ctl_events, on, &wake_poller);
+    old_events = state->events;
 
-    if (new_events & (ERTS_POLL_EV_ERR|ERTS_POLL_EV_NVAL)) {
-	if (state->type == ERTS_EV_TYPE_NIF && !state->events) {
-	    state->type = ERTS_EV_TYPE_NONE;
-	    state->flags &= ~ERTS_EV_FLAG_USED;
-	    state->driver.nif->in.pid = NIL;
-	    state->driver.nif->out.pid = NIL;
-            state->driver.nif->in.ddeselect_cnt = 0;
-            state->driver.nif->out.ddeselect_cnt = 0;
-            state->driver.stop.resource = NULL;
-	}
-	ret = INT_MIN | ERL_NIF_SELECT_FAILED;
-	goto done;
+    if (on) {
+        ctl_events &= ~old_events;
+        state->events |= ctl_events;
+        state->active_events |= ctl_events;
+        if (state->type == ERTS_EV_TYPE_NONE)
+            ctl_op = ERTS_POLL_OP_ADD;
+    }
+    else {
+        ctl_events &= old_events;
+        state->events &= ~ctl_events;
+        state->active_events &= ~ctl_events;
     }
 
-    old_events = state->events;
+    if (ctl_events || ctl_op == ERTS_POLL_OP_DEL) {
+        ErtsPollEvents new_events;
 
-    ASSERT(on
-	   ? (new_events == (state->events | ctl_events))
-	   : (new_events == (state->events & ~ctl_events)));
+        new_events = erts_io_control_wakeup(state, ctl_op,
+                                            state->active_events,
+                                            &wake_poller);
+
+        if (new_events & (ERTS_POLL_EV_ERR|ERTS_POLL_EV_NVAL)) {
+            if (state->type == ERTS_EV_TYPE_NIF && !old_events) {
+                state->type = ERTS_EV_TYPE_NONE;
+                state->flags = 0;
+                state->driver.nif->in.pid = NIL;
+                state->driver.nif->out.pid = NIL;
+                state->driver.stop.resource = NULL;
+            }
+            ret = INT_MIN | ERL_NIF_SELECT_FAILED;
+            goto done;
+        }
+        ASSERT(new_events == state->events);
+    }
 
     ASSERT(state->type == ERTS_EV_TYPE_NIF
 	   || state->type == ERTS_EV_TYPE_NONE);
 
-    state->events = new_events;
     if (on) {
         const Eterm recipient = pid ? pid->pid : env->proc->common.id;
         Uint32* refn;
@@ -1332,7 +1015,7 @@ ERTS_CIO_EXPORT(enif_select)(ErlNifEnv* env,
         }
         ASSERT(state->type == ERTS_EV_TYPE_NIF);
         ASSERT(state->driver.stop.resource == resource);
-        if (ctl_events & ERTS_POLL_EV_IN) {
+        if (mode & ERL_DRV_READ) {
             state->driver.nif->in.pid = recipient;
             if (is_immed(ref)) {
                 state->driver.nif->in.immed = ref;
@@ -1340,13 +1023,11 @@ ERTS_CIO_EXPORT(enif_select)(ErlNifEnv* env,
                 ASSERT(is_internal_ref(ref));
                 refn = internal_ref_numbers(ref);
                 state->driver.nif->in.immed = THE_NON_VALUE;
-                state->driver.nif->in.refn[0] = refn[0];
-                state->driver.nif->in.refn[1] = refn[1];
-                state->driver.nif->in.refn[2] = refn[2];
+                sys_memcpy(state->driver.nif->in.refn, refn,
+                           sizeof(state->driver.nif->in.refn));
             }
-            state->driver.nif->in.ddeselect_cnt = 0;
         }
-        if (ctl_events & ERTS_POLL_EV_OUT) {
+        if (mode & ERL_DRV_WRITE) {
             state->driver.nif->out.pid = recipient;
             if (is_immed(ref)) {
                 state->driver.nif->out.immed = ref;
@@ -1354,11 +1035,9 @@ ERTS_CIO_EXPORT(enif_select)(ErlNifEnv* env,
                 ASSERT(is_internal_ref(ref));
                 refn = internal_ref_numbers(ref);
                 state->driver.nif->out.immed = THE_NON_VALUE;
-                state->driver.nif->out.refn[0] = refn[0];
-                state->driver.nif->out.refn[1] = refn[1];
-                state->driver.nif->out.refn[2] = refn[2];
+                sys_memcpy(state->driver.nif->out.refn, refn,
+                           sizeof(state->driver.nif->out.refn));
             }
-            state->driver.nif->out.ddeselect_cnt = 0;
         }
         ret = 0;
     }
@@ -1366,14 +1045,9 @@ ERTS_CIO_EXPORT(enif_select)(ErlNifEnv* env,
         if (state->type == ERTS_EV_TYPE_NIF) {
             state->driver.nif->in.pid = NIL;
             state->driver.nif->out.pid = NIL;
-            state->driver.nif->in.ddeselect_cnt = 0;
-            state->driver.nif->out.ddeselect_cnt = 0;
-            if (old_events != 0) {
-                remember_removed(state, &pollset);
-            }
         }
-        ASSERT(new_events==0);
-        if (state->remove_cnt == 0 || !wake_poller) {
+        ASSERT(state->events==0);
+        if (!wake_poller) {
             /*
              * Safe to close fd now as it is not in pollset
              * or there was no need to eject fd (kernel poll)
@@ -1405,9 +1079,6 @@ ERTS_CIO_EXPORT(enif_select)(ErlNifEnv* env,
 done:
 
     check_fd_cleanup(state,
-#if ERTS_CIO_HAVE_DRV_EVENT
-		     &free_event,
-#endif
 		     &free_select,
                      &free_nif);
 
@@ -1424,160 +1095,7 @@ done_unknown:
     if (free_nif)
         free_nif_select_data(free_nif);
 
-#if ERTS_CIO_HAVE_DRV_EVENT
-    if (free_event)
-	free_drv_event_data(free_event);
-#endif
-    return ret;
-}
-
-
-int
-ERTS_CIO_EXPORT(driver_event)(ErlDrvPort ix,
-			      ErlDrvEvent e,
-			      ErlDrvEventData event_data)
-{
-#if !ERTS_CIO_HAVE_DRV_EVENT
-    return -1;
-#else
-    ErtsSysFdType fd = (ErtsSysFdType) e;
-    ErtsPollEvents events;
-    ErtsPollEvents add_events;
-    ErtsPollEvents remove_events;
-    Eterm id = erts_drvport2id(ix);
-    ErtsDrvEventState *state;
-    int do_wake = 0;
-    int ret;
-#if ERTS_CIO_HAVE_DRV_EVENT
-    ErtsDrvEventDataState *free_event;
-#endif
-    ErtsDrvSelectDataState *free_select;
-    ErtsNifSelectDataState *free_nif;
-    Port *prt = erts_drvport2port(ix);
-
-    if (prt == ERTS_INVALID_ERL_DRV_PORT)
-	return -1;
-
-    ERTS_LC_ASSERT(erts_lc_is_port_locked(prt));
-
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    if ((unsigned)fd >= (unsigned)erts_atomic_read_nob(&drv_ev_state_len)) {
-	if (fd < 0)
-	    return -1;    
-	if (fd >= max_fds) {
-	    event_large_fd_error(ix, fd, event_data);
-	    return -1;
-	}
-	grow_drv_ev_state(fd);
-    }
-#endif
-
-    erts_mtx_lock(fd_mtx(fd));
-
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    state = &drv_ev_state[(int) fd];
-#else
-    /* Could use hash_new directly, but want to keep the normal case fast */
-    state = hash_get_drv_ev_state(fd);
-    if (state == NULL) {
-	state = hash_new_drv_ev_state(fd);
-    }
-#endif
-
-    switch (state->type) {
-    case ERTS_EV_TYPE_DRV_EV:
-	if (state->driver.event->port == id) break;
-	/*fall through*/
-    case ERTS_EV_TYPE_DRV_SEL:
-	drv_event_steal(ix, state, event_data);
-	break;
-    case ERTS_EV_TYPE_STOP_USE: {
-	erts_dsprintf_buf_t *dsbufp = erts_create_logger_dsbuf();
-	print_drv_event_op(dsbufp, ix, fd, event_data);
-	steal_pending_stop_use(dsbufp, ix, state, 0, 1);
-	break;
-      }
-    }
-
-    ASSERT(state->type == ERTS_EV_TYPE_DRV_EV
-	   || state->type == ERTS_EV_TYPE_NONE);
-
-    events = state->events;
-
-    if (!event_data) {
-	remove_events = events;
-	add_events = 0;
-    }
-    else {
-	remove_events = ~event_data->events & events;
-	add_events = ~events & event_data->events;
-    }
-
-    if (add_events) {
-	events = ERTS_CIO_POLL_CTL(pollset.ps, state->fd, add_events, 1, &do_wake);
-	if (events & (ERTS_POLL_EV_ERR|ERTS_POLL_EV_NVAL)) {
-	    ret = -1;
-	    goto done;
-	}
-    }
-    if (remove_events) {
-	events = ERTS_CIO_POLL_CTL(pollset.ps, state->fd, remove_events, 0, &do_wake);
-	if (events & (ERTS_POLL_EV_ERR|ERTS_POLL_EV_NVAL)) {
-	    ret = -1;
-	    goto done;
-	}
-    }
-    if (event_data && event_data->events != 0) {
-	if (state->type == ERTS_EV_TYPE_DRV_EV) {
-	    state->driver.event->removed_events &= ~add_events;
-	    state->driver.event->removed_events |= remove_events;
-	}
-	else {
-	    if (!state->driver.event)
-		state->driver.event = alloc_drv_event_data();
-	    state->driver.event->port = id;
-	    state->driver.event->removed_events = (ErtsPollEvents) 0;
-	    state->type = ERTS_EV_TYPE_DRV_EV;
-	}
-	state->driver.event->data = event_data;
-    }
-    else {
-	if (state->type == ERTS_EV_TYPE_DRV_EV) {
-	    abort_tasks(state, 0);
-	    state->driver.event->port = NIL;
-	    state->driver.event->data = NULL;
-	    state->driver.event->removed_events = (ErtsPollEvents) 0;
-	}
-	state->type = ERTS_EV_TYPE_NONE;
-	remember_removed(state, &pollset);
-    }
-    state->events = events;
-    ASSERT(event_data ? events == event_data->events : events == 0); 
-
-    ret = 0;
-
-done:
-
-    check_fd_cleanup(state,
-#if ERTS_CIO_HAVE_DRV_EVENT
-		     &free_event,
-#endif
-		     &free_select,
-                     &free_nif);
-
-    erts_mtx_unlock(fd_mtx(fd));
-
-    if (free_select)
-	free_drv_select_data(free_select);
-    if (free_nif)
-        free_nif_select_data(free_nif);
-#if ERTS_CIO_HAVE_DRV_EVENT
-    if (free_event)
-	free_drv_event_data(free_event);
-#endif
-
     return ret;
-#endif
 }
 
 static ERTS_INLINE int
@@ -1611,11 +1129,6 @@ need2steal(ErtsDrvEventState *state, int mode)
         do_steal = 1;
         break;
 
-#if ERTS_CIO_HAVE_DRV_EVENT
-    case ERTS_EV_TYPE_DRV_EV:
-	do_steal |= chk_stale(state->driver.event->port, state, 0);
-	break;
-#endif
     case ERTS_EV_TYPE_STOP_USE:
     case ERTS_EV_TYPE_STOP_NIF:
         ASSERT(0);
@@ -1649,7 +1162,7 @@ print_driver_name(erts_dsprintf_buf_t *dsbufp, Eterm id)
 static void
 steal(erts_dsprintf_buf_t *dsbufp, ErtsDrvEventState *state, int mode)
 {
-    erts_dsprintf(dsbufp, "stealing control of fd=%d from ", (int) GET_FD(state->fd));
+    erts_dsprintf(dsbufp, "stealing control of fd=%d from ", (int) state->fd);
     switch (state->type) {
     case ERTS_EV_TYPE_DRV_SEL: {
 	int deselect_mode = 0;
@@ -1673,7 +1186,7 @@ steal(erts_dsprintf_buf_t *dsbufp, ErtsDrvEventState *state, int mode)
 	if (deselect_mode)
 	    deselect(state, deselect_mode);
 	else {
-	    erts_dsprintf(dsbufp, "no one", (int) GET_FD(state->fd));
+	    erts_dsprintf(dsbufp, "no one", (int) state->fd);
 	    ASSERT(0);
 	}
 	erts_dsprintf(dsbufp, "\n");
@@ -1698,30 +1211,13 @@ steal(erts_dsprintf_buf_t *dsbufp, ErtsDrvEventState *state, int mode)
         erts_dsprintf(dsbufp, "\n");
         break;
     }
-#if ERTS_CIO_HAVE_DRV_EVENT
-    case ERTS_EV_TYPE_DRV_EV: {
-	Eterm eid = state->driver.event->port;
-	if (is_nil(eid)) {
-	    erts_dsprintf(dsbufp, "no one", (int) state->fd);
-	    ASSERT(0);
-	}
-	else {
-	    erts_dsprintf(dsbufp, "event driver ");
-	    print_driver_name(dsbufp, eid);
-	    erts_dsprintf(dsbufp, "%T ", eid);
-	}
-	erts_dsprintf(dsbufp, "\n");
-	deselect(state, 0);
-	break;
-    }
-#endif
     case ERTS_EV_TYPE_STOP_USE:
     case ERTS_EV_TYPE_STOP_NIF: {
 	ASSERT(0);
 	break;
     }
     default:
-	erts_dsprintf(dsbufp, "no one\n", (int) GET_FD(state->fd));
+	erts_dsprintf(dsbufp, "no one\n", (int) state->fd);
 	ASSERT(0);
     }
 }
@@ -1735,7 +1231,7 @@ print_drv_select_op(erts_dsprintf_buf_t *dsbufp,
 		  "driver_select(%p, %d,%s%s%s%s, %d) "
 		  "by ",
 		  ix,
-		  (int) GET_FD(fd),
+		  (int) fd,
 		  mode & ERL_DRV_READ ? " ERL_DRV_READ" : "",
 		  mode & ERL_DRV_WRITE ? " ERL_DRV_WRITE" : "",
 		  mode & ERL_DRV_USE ? " ERL_DRV_USE" : "",
@@ -1752,7 +1248,7 @@ print_nif_select_op(erts_dsprintf_buf_t *dsbufp,
 {
     erts_dsprintf(dsbufp,
 		  "enif_select(_, %d,%s%s%s, %T:%T, %T) ",
-		  (int) GET_FD(fd),
+		  (int) fd,
 		  mode & ERL_NIF_SELECT_READ ? " READ" : "",
 		  mode & ERL_NIF_SELECT_WRITE ? " WRITE" : "",
 		  mode & ERL_NIF_SELECT_STOP ? " STOP" : "",
@@ -1791,7 +1287,7 @@ large_fd_error_common(erts_dsprintf_buf_t *dsbufp, ErtsSysFdType fd)
 {
     erts_dsprintf(dsbufp,
 		  "fd=%d is larger than the largest allowed fd=%d\n",
-		  (int) fd, max_fds - 1);
+		  (int) fd, drv_ev_state.max_fds - 1);
 }
 
 static void
@@ -1847,7 +1343,7 @@ steal_pending_stop_use(erts_dsprintf_buf_t *dsbufp, ErlDrvPort ix,
             erts_ddll_dereference_driver(state->driver.stop.drv_ptr->handle);
         }
         state->type = ERTS_EV_TYPE_NONE;
-        state->flags &= ~ERTS_EV_FLAG_USED;
+        state->flags = 0;
         state->driver.stop.drv_ptr = NULL;
     }
     else {
@@ -1884,9 +1380,9 @@ steal_pending_stop_nif(erts_dsprintf_buf_t *dsbufp, ErtsResource* resource,
         erts_dsprintf(dsbufp, "called before stop was called for NIF resource %T:%T\n",
                       rt->module, rt->name);
 
-        enif_release_resource(state->driver.stop.resource);
+        enif_release_resource(state->driver.stop.resource->data);
         state->type = ERTS_EV_TYPE_NONE;
-        state->flags &= ~ERTS_EV_FLAG_USED;
+        state->flags = 0;
         state->driver.stop.resource = NULL;
     }
     else {
@@ -1896,59 +1392,9 @@ steal_pending_stop_nif(erts_dsprintf_buf_t *dsbufp, ErtsResource* resource,
 
 }
 
-
-#if ERTS_CIO_HAVE_DRV_EVENT
-
-static void
-print_drv_event_op(erts_dsprintf_buf_t *dsbufp,
-                   ErlDrvPort ix, ErtsSysFdType fd, ErlDrvEventData event_data)
-{
-    Port *pp = erts_drvport2port(ix);
-    erts_dsprintf(dsbufp, "driver_event(%p, %d, ", ix, (int) fd);
-    if (!event_data)
-	erts_dsprintf(dsbufp, "NULL");
-    else
-	erts_dsprintf(dsbufp, "{0x%x, 0x%x}",
-		      (unsigned int) event_data->events,
-		      (unsigned int) event_data->revents);
-    erts_dsprintf(dsbufp, ") by ");
-    if (pp != ERTS_INVALID_ERL_DRV_PORT)
-	print_driver_name(dsbufp, pp->common.id);
-    erts_dsprintf(dsbufp, "driver %T ", pp != ERTS_INVALID_ERL_DRV_PORT ? pp->common.id : NIL);
-}
-
-static void
-drv_event_steal(ErlDrvPort ix, ErtsDrvEventState *state, ErlDrvEventData event_data)
-{
-    if (need2steal(state, ERL_DRV_READ|ERL_DRV_WRITE)) {
-	erts_dsprintf_buf_t *dsbufp = erts_create_logger_dsbuf();
-	print_drv_event_op(dsbufp, ix, state->fd, event_data);
-	steal(dsbufp, state, ERL_DRV_READ|ERL_DRV_WRITE);
-	erts_send_error_to_logger_nogl(dsbufp);
-    }
-    else if (state->type == ERTS_EV_TYPE_DRV_SEL) {
-	ASSERT(state->flags & ERTS_EV_FLAG_USED);
-	deselect(state, 0);
-    }
-}
-
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-static void
-event_large_fd_error(ErlDrvPort ix, ErtsSysFdType fd, ErlDrvEventData event_data)
-{
-    erts_dsprintf_buf_t *dsbufp = erts_create_logger_dsbuf();
-    print_drv_event_op(dsbufp, ix, fd, event_data);
-    erts_dsprintf(dsbufp, "failed: ");
-    large_fd_error_common(dsbufp, fd);
-    erts_send_error_to_logger_nogl(dsbufp);
-}
-#endif
-#endif
-
 static ERTS_INLINE int
 io_task_schedule_allowed(ErtsDrvEventState *state,
-			 ErtsPortTaskType type,
-			 erts_aint_t current_cio_time)
+			 ErtsPortTaskType type)
 {
     ErtsIoTask *io_task;
 
@@ -1956,71 +1402,53 @@ io_task_schedule_allowed(ErtsDrvEventState *state,
     case ERTS_PORT_TASK_INPUT:
 	if (!state->driver.select)
 	    return 0;
-#if ERTS_CIO_HAVE_DRV_EVENT
-	if (state->driver.event)
-	    return 0;
-#endif
 	io_task = &state->driver.select->iniotask;
 	break;
     case ERTS_PORT_TASK_OUTPUT:
 	if (!state->driver.select)
 	    return 0;
-#if ERTS_CIO_HAVE_DRV_EVENT
-	if (state->driver.event)
-	    return 0;
-#endif
 	io_task = &state->driver.select->outiotask;
 	break;
-#if ERTS_CIO_HAVE_DRV_EVENT
-    case ERTS_PORT_TASK_EVENT:
-	if (!state->driver.event)
-	    return 0;
-	if (state->driver.select)
-	    return 0;
-	io_task = &state->driver.event->iotask;
-	break;
-#endif
     default:
 	ERTS_INTERNAL_ERROR("Invalid I/O-task type");
 	return 0;
     }
 
-    return !is_iotask_active(io_task, current_cio_time);
+    return !is_iotask_active(io_task);
 }
 
 static ERTS_INLINE void
-iready(Eterm id, ErtsDrvEventState *state, erts_aint_t current_cio_time)
+iready(Eterm id, ErtsDrvEventState *state)
 {
     if (io_task_schedule_allowed(state,
-				 ERTS_PORT_TASK_INPUT,
-				 current_cio_time)) {
+				 ERTS_PORT_TASK_INPUT)) {
 	ErtsIoTask *iotask = &state->driver.select->iniotask;
-	erts_atomic_set_nob(&iotask->executed_time, current_cio_time);
 	if (erts_port_task_schedule(id,
 				    &iotask->task,
 				    ERTS_PORT_TASK_INPUT,
 				    (ErlDrvEvent) state->fd) != 0) {
 	    stale_drv_select(id, state, ERL_DRV_READ);
-	}
-	add_active_fd(state->fd);
+	} else {
+            DEBUG_PRINT_FD("schedule ready_input(%T, %d)",
+                           state, id, state->fd);
+        }
     }
 }
 
 static ERTS_INLINE void
-oready(Eterm id, ErtsDrvEventState *state, erts_aint_t current_cio_time)
+oready(Eterm id, ErtsDrvEventState *state)
 {
     if (io_task_schedule_allowed(state,
-				 ERTS_PORT_TASK_OUTPUT,
-				 current_cio_time)) {
+				 ERTS_PORT_TASK_OUTPUT)) {
 	ErtsIoTask *iotask = &state->driver.select->outiotask;
-	erts_atomic_set_nob(&iotask->executed_time, current_cio_time);
 	if (erts_port_task_schedule(id,
 				    &iotask->task,
 				    ERTS_PORT_TASK_OUTPUT,
 				    (ErlDrvEvent) state->fd) != 0) {
 	    stale_drv_select(id, state, ERL_DRV_WRITE);
-	}
-	add_active_fd(state->fd);
+	} else {
+            DEBUG_PRINT_FD("schedule ready_output(%T, %d)", state, id, state->fd);
+        }
     }
 }
 
@@ -2072,131 +1500,59 @@ send_event_tuple(struct erts_nif_select_event* e, ErtsResource* resource,
         erts_proc_unlock(rp, rp_locks);
 }
 
-
-#if ERTS_CIO_HAVE_DRV_EVENT
-static ERTS_INLINE void
-eready(Eterm id, ErtsDrvEventState *state, ErlDrvEventData event_data,
-       erts_aint_t current_cio_time)
-{
-    if (io_task_schedule_allowed(state,
-				 ERTS_PORT_TASK_EVENT,
-				 current_cio_time)) {
-	ErtsIoTask *iotask = &state->driver.event->iotask;
-	erts_atomic_set_nob(&iotask->executed_time, current_cio_time);
-	if (erts_port_task_schedule(id,
-				    &iotask->task,
-				    ERTS_PORT_TASK_EVENT,
-				    (ErlDrvEvent) state->fd,
-				    event_data) != 0) {
-	    stale_drv_select(id, state, 0);
-	}
-	add_active_fd(state->fd);
-    }
-}
-#endif
-
 static void bad_fd_in_pollset(ErtsDrvEventState *, Eterm inport, Eterm outport);
 
-
 void
-ERTS_CIO_EXPORT(erts_check_io_interrupt)(int set)
+erts_check_io_interrupt(ErtsPollThread *psi, int set)
 {
-    ERTS_CIO_POLL_INTR(pollset.ps, set);
+    if (psi) {
+#if ERTS_POLL_USE_FALLBACK
+        if (psi->ps == get_fallback()) {
+            erts_poll_interrupt_flbk(psi->ps, set);
+            return;
+        }
+#endif
+        erts_poll_interrupt(psi->ps, set);
+    }
 }
 
-void
-ERTS_CIO_EXPORT(erts_check_io_interrupt_timed)(int set,
-					       ErtsMonotonicTime timeout_time)
-{
-    ERTS_CIO_POLL_INTR_TMD(pollset.ps, set, timeout_time);
+ErtsPollThread *
+erts_create_pollset_thread(int id) {
+    return psiv+id;
 }
 
-#if !ERTS_CIO_DEFER_ACTIVE_EVENTS
-/*
- * Number of ignored events, for a lingering fd added by enif_select(),
- * until we deselect fd-event from pollset.
- */
-# define ERTS_NIF_DELAYED_DESELECT 20
-#else
-/* Disable delayed deselect as pollset cannot handle active events */
-# define ERTS_NIF_DELAYED_DESELECT 1
-#endif
-
 void
-ERTS_CIO_EXPORT(erts_check_io)(int do_wait)
+erts_check_io(ErtsPollThread *psi)
 {
-    ErtsPollResFd *pollres;
     int pollres_len;
-    ErtsMonotonicTime timeout_time;
     int poll_ret, i;
-    erts_aint_t current_cio_time;
-    ErtsSchedulerData *esdp = erts_get_scheduler_data();
-
-    ASSERT(esdp);
+    ERTS_MSACC_PUSH_AND_SET_STATE(ERTS_MSACC_STATE_CHECK_IO);
 
  restart:
 
-#ifdef ERTS_BREAK_REQUESTED
-    if (ERTS_BREAK_REQUESTED)
-	erts_do_break_handling();
-#endif
-
-#ifdef ERTS_SIGNAL_STATE /* ifndef ERTS_SMP */
-    if (ERTS_SIGNAL_STATE) {
-        erts_handle_signal_state();
-    }
-#endif
-
-    /* Figure out timeout value */
-    timeout_time = (do_wait
-		    ? erts_check_next_timeout_time(esdp)
-		    : ERTS_POLL_NO_TIMEOUT /* poll only */);
-
-    /*
-     * No need for an atomic inc op when incrementing
-     * erts_check_io_time, since only one thread can
-     * check io at a time.
-     */
-    current_cio_time = erts_atomic_read_dirty(&erts_check_io_time);
-    current_cio_time++;
-    erts_atomic_set_relb(&erts_check_io_time, current_cio_time);
-
-    check_cleanup_active_fds(current_cio_time,
-                             timeout_time != ERTS_POLL_NO_TIMEOUT);
-
 #ifdef ERTS_ENABLE_LOCK_CHECK
     erts_lc_check_exact(NULL, 0); /* No locks should be locked */
 #endif
 
-    pollres_len = erts_atomic32_read_dirty(&pollset.active_fd.no) + ERTS_CHECK_IO_POLL_RES_LEN;
+    pollres_len = psi->pollres_len;
 
-    pollres = erts_alloc(ERTS_ALC_T_TMP, sizeof(ErtsPollResFd)*pollres_len);
+#if ERTS_POLL_USE_FALLBACK
+    if (psi->ps == get_fallback()) {
 
-    erts_atomic_set_nob(&pollset.in_poll_wait, 1);
+        poll_ret = erts_poll_wait_flbk(psi->ps, psi->pollres, &pollres_len);
 
-    poll_ret = ERTS_CIO_POLL_WAIT(pollset.ps, pollres, &pollres_len, timeout_time);
+    } else
+#endif
+    {
+        poll_ret = erts_poll_wait(psi->ps, psi->pollres, &pollres_len);
+    }
 
 #ifdef ERTS_ENABLE_LOCK_CHECK
     erts_lc_check_exact(NULL, 0); /* No locks should be locked */
 #endif
 
-#ifdef ERTS_BREAK_REQUESTED
-    if (ERTS_BREAK_REQUESTED)
-	erts_do_break_handling();
-#endif
-
-
-#ifdef ERTS_SIGNAL_STATE /* ifndef ERTS_SMP */
-    if (ERTS_SIGNAL_STATE) {
-        erts_handle_signal_state();
-    }
-#endif
-
-
     if (poll_ret != 0) {
-	erts_atomic_set_nob(&pollset.in_poll_wait, 0);
-	forget_removed(&pollset);
-	erts_free(ERTS_ALC_T_TMP, pollres);
+
 	if (poll_ret == EAGAIN) {
 	    goto restart;
 	}
@@ -2212,65 +1568,86 @@ ERTS_CIO_EXPORT(erts_check_io)(int do_wait)
 			  erl_errno_id(poll_ret), poll_ret);
 	    erts_send_error_to_logger_nogl(dsbufp);
 	}
+        ERTS_MSACC_POP_STATE();
 	return;
     }
 
     for (i = 0; i < pollres_len; i++) {
 
-	ErtsSysFdType fd = (ErtsSysFdType) pollres[i].fd;
+        erts_driver_t* drv_ptr = NULL;
+        ErtsResource* resource = NULL;
+        ErtsDrvSelectDataState *free_select = NULL;
+        ErtsNifSelectDataState *free_nif = NULL;
+	ErtsSysFdType fd = (ErtsSysFdType) ERTS_POLL_RES_GET_FD(&psi->pollres[i]);
 	ErtsDrvEventState *state;
+        ErtsPollEvents revents;
 
 	erts_mtx_lock(fd_mtx(fd));
 
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-	state = &drv_ev_state[ (int) fd];
-#else
-	state = hash_get_drv_ev_state(fd);
+	state = get_drv_ev_state(fd);
+
 	if (!state) {
-	    goto next_pollres;
+            erts_mtx_unlock(fd_mtx(fd));
+            continue;
 	}
-#endif
 
-	/* Skip this fd if it was removed from pollset */
-	if (is_removed(state)) {
-	    goto next_pollres;
-	}
+        revents = ERTS_POLL_RES_GET_EVTS(&psi->pollres[i]);
+
+        DEBUG_PRINT_FD("triggered %s", state, ev2str(revents));
+
+        if (revents & ERTS_POLL_EV_ERR) {
+            /*
+             * Handle error events by triggering all in/out events
+             * that has been selected on.
+             * We *do not* want to call a callback that corresponds
+             * to an event not selected.
+             */
+            revents = state->active_events;
+            state->active_events = 0;
+        } else {
+
+            /* Disregard any events that are not active at the moment,
+               for instance this could happen if the driver/nif does
+               select/deselect in rapid succession. */
+            revents &= state->active_events | ERTS_POLL_EV_NVAL;
+            state->active_events &= ~revents;
+
+            /* Reactivate the poll op if there are still active events */
+            if (state->active_events) {
+                ErtsPollEvents new_events;
+                DEBUG_PRINT_FD("re-enable %s", state, ev2str(state->active_events));
+
+                new_events = erts_io_control(state, ERTS_POLL_OP_MOD, state->active_events);
+
+                /* Unable to re-enable the fd, signal all callbacks */
+                if (new_events & (ERTS_POLL_EV_ERR|ERTS_POLL_EV_NVAL)) {
+                    revents |= state->active_events;
+                    state->active_events = 0;
+                }
+            }
+        }
 
 	switch (state->type) {
 	case ERTS_EV_TYPE_DRV_SEL: { /* Requested via driver_select()... */
-	    ErtsPollEvents revents = pollres[i].events;
-
-            if (revents & ERTS_POLL_EV_ERR) {
-                /*
-                 * Handle error events by triggering all in/out events
-                 * that the driver has selected.
-                 * We *do not* want to call a callback that corresponds
-		 * to an event not selected.
-                 */
-                revents = state->events;
-            }
-            else {
-                revents &= (state->events | ERTS_POLL_EV_NVAL);
-            }
 
             if (revents & (ERTS_POLL_EV_IN|ERTS_POLL_EV_OUT)) {
 		if (revents & ERTS_POLL_EV_OUT) {
-		    oready(state->driver.select->outport, state, current_cio_time);
+		    oready(state->driver.select->outport, state);
 		}
 		/* Someone might have deselected input since revents
 		   was read (true also on the non-smp emulator since
 		   oready() may have been called); therefore, update
 		   revents... */
-		revents &= state->events;
+                revents &= state->events;
 		if (revents & ERTS_POLL_EV_IN) {
-		    iready(state->driver.select->inport, state, current_cio_time);
+		    iready(state->driver.select->inport, state);
 		}
 	    }
 	    else if (revents & ERTS_POLL_EV_NVAL) {
 		bad_fd_in_pollset(state,
                                   state->driver.select->inport,
                                   state->driver.select->outport);
-		add_active_fd(state->fd);
+                check_fd_cleanup(state, &free_select, &free_nif);
 	    }
 	    break;
 	}
@@ -2279,108 +1656,116 @@ ERTS_CIO_EXPORT(erts_check_io)(int do_wait)
             struct erts_nif_select_event in = {NIL};
             struct erts_nif_select_event out = {NIL};
             ErtsResource* resource = NULL;
-            ErtsPollEvents revents = pollres[i].events;
-
-            if (revents & ERTS_POLL_EV_ERR) {
-                /*
-                 * Handle error events by triggering all in/out events
-                 * that the NIF has selected.
-                 * We *do not* want to send a message that corresponds
-		 * to an event not selected.
-                 */
-                revents = state->events;
-            }
-            else {
-                revents &= (state->events | ERTS_POLL_EV_NVAL);
-            }
 
             if (revents & (ERTS_POLL_EV_IN|ERTS_POLL_EV_OUT)) {
                 if (revents & ERTS_POLL_EV_OUT) {
                     if (is_not_nil(state->driver.nif->out.pid)) {
                         out = state->driver.nif->out;
                         resource = state->driver.stop.resource;
-                        state->driver.nif->out.ddeselect_cnt = ERTS_NIF_DELAYED_DESELECT;
                         state->driver.nif->out.pid = NIL;
-                        add_active_fd(state->fd);
-                    }
-                    else {
-                        ASSERT(state->driver.nif->out.ddeselect_cnt >= 2);
-                        state->driver.nif->out.ddeselect_cnt--;
                     }
                 }
                 if (revents & ERTS_POLL_EV_IN) {
                     if (is_not_nil(state->driver.nif->in.pid)) {
                         in = state->driver.nif->in;
                         resource = state->driver.stop.resource;
-                        state->driver.nif->in.ddeselect_cnt = ERTS_NIF_DELAYED_DESELECT;
                         state->driver.nif->in.pid = NIL;
-                        add_active_fd(state->fd);
-                    }
-                    else {
-                        ASSERT(state->driver.nif->in.ddeselect_cnt >= 2);
-                        state->driver.nif->in.ddeselect_cnt--;
                     }
                 }
+                state->events &= ~revents;
             }
             else if (revents & ERTS_POLL_EV_NVAL) {
                 bad_fd_in_pollset(state, NIL, NIL);
-                add_active_fd(state->fd);
+                check_fd_cleanup(state, &free_select, &free_nif);
             }
 
             erts_mtx_unlock(fd_mtx(fd));
+
             if (is_not_nil(in.pid)) {
                 send_event_tuple(&in, resource, am_ready_input);
             }
             if (is_not_nil(out.pid)) {
                 send_event_tuple(&out, resource, am_ready_output);
             }
-            goto next_pollres_unlocked;
+            continue;
         }
 
-#if ERTS_CIO_HAVE_DRV_EVENT
-	case ERTS_EV_TYPE_DRV_EV: { /* Requested via driver_event()... */
-	    ErlDrvEventData event_data;
-	    ErtsPollEvents revents;
-	    ASSERT(state->driver.event);
-	    ASSERT(state->driver.event->data);
-	    event_data = state->driver.event->data;
-	    revents = pollres[i].events;
-	    revents &= ~state->driver.event->removed_events;
-
-	    if (revents) {
-		event_data->events = state->events;
-		event_data->revents = revents;
-		eready(state->driver.event->port, state, event_data, current_cio_time);
-	    }
-	    break;
-	}
-#endif
+        case ERTS_EV_TYPE_STOP_NIF: {
+            resource = state->driver.stop.resource;
+            state->type = ERTS_EV_TYPE_NONE;
+            goto case_ERTS_EV_TYPE_NONE;
+        }
 
+        case ERTS_EV_TYPE_STOP_USE: {
+#if ERTS_POLL_USE_FALLBACK
+            ASSERT(psi->ps == get_fallback());
+#endif
+            drv_ptr = state->driver.stop.drv_ptr;
+            state->type = ERTS_EV_TYPE_NONE;
+            /* fallthrough */
 	case ERTS_EV_TYPE_NONE: /* Deselected ... */
+        case_ERTS_EV_TYPE_NONE:
+            ASSERT(!state->events && !state->active_events && !state->flags);
+            check_fd_cleanup(state, &free_select, &free_nif);
 	    break;
+        }
 
 	default: { /* Error */
 	    erts_dsprintf_buf_t *dsbufp;
 	    dsbufp = erts_create_logger_dsbuf();
 	    erts_dsprintf(dsbufp,
 			  "Invalid event request type for fd in erts_poll()! "
-			  "fd=%d, event request type=%sd\n", (int) state->fd,
+			  "fd=%d, event request type=%d\n", (int) state->fd,
 			  (int) state->type);
 	    ASSERT(0);
 	    deselect(state, 0);
-	    add_active_fd(state->fd);
 	    break;
 	}
 	}
 
-	next_pollres:;
 	erts_mtx_unlock(fd_mtx(fd));
-        next_pollres_unlocked:;
-    }
 
-    erts_atomic_set_nob(&pollset.in_poll_wait, 0);
-    erts_free(ERTS_ALC_T_TMP, pollres);
-    forget_removed(&pollset);
+        if (drv_ptr) {
+            int was_unmasked = erts_block_fpe();
+            DTRACE1(driver_stop_select, drv_ptr->name);
+            LTTNG1(driver_stop_select, drv_ptr->name);
+            (*drv_ptr->stop_select)((ErlDrvEvent) fd, NULL);
+            erts_unblock_fpe(was_unmasked);
+            if (drv_ptr->handle) {
+		erts_ddll_dereference_driver(drv_ptr->handle);
+	    }
+        }
+        if (resource) {
+            erts_resource_stop(resource, (ErlNifEvent)fd, 1);
+            enif_release_resource(resource->data);
+        }
+        if (free_select)
+            free_drv_select_data(free_select);
+        if (free_nif)
+            free_nif_select_data(free_nif);
+    }
+
+    /* The entire pollres array was filled with events,
+     * grow it for the next call. We do this for two reasons:
+     * 1. Pulling out more events in on go will increase throughput
+     * 2. If the polling implementation is not fair, this will make
+     *    sure that we get all fds that we can. i.e. if 12 fds are
+     *    constantly active, but we only have a pollres_len of 10,
+     *    two of the fds may never be triggered depending on what the
+     *    kernel decides to do.
+     **/
+    if (pollres_len == psi->pollres_len) {
+        int ev_state_len = drv_ev_state_len();
+        erts_free(ERTS_ALC_T_POLLSET, psi->pollres);
+        psi->pollres_len *= 2;
+        /* Never grow it larger than the current drv_ev_state.len size */
+        if (psi->pollres_len > ev_state_len)
+            psi->pollres_len = ev_state_len;
+        psi->pollres = erts_alloc(ERTS_ALC_T_POLLSET,
+                                  sizeof(ErtsPollResFd) * psi->pollres_len);
+    }
+
+    ERTS_MSACC_POP_STATE();
 }
 
 static void
@@ -2474,16 +1859,16 @@ static int drv_ev_state_cmp(void *des1, void *des2)
 static void *drv_ev_state_alloc(void *des_tmpl)
 {
     ErtsDrvEventState *evstate;
-    erts_spin_lock(&state_prealloc_lock);
-    if (state_prealloc_first == NULL) {
-	erts_spin_unlock(&state_prealloc_lock);
+    erts_spin_lock(&drv_ev_state.prealloc_lock);
+    if (drv_ev_state.prealloc_first == NULL) {
+	erts_spin_unlock(&drv_ev_state.prealloc_lock);
 	evstate = (ErtsDrvEventState *) 
 	    erts_alloc(ERTS_ALC_T_DRV_EV_STATE, sizeof(ErtsDrvEventState));
     } else {
-	evstate = state_prealloc_first;
-	state_prealloc_first = (ErtsDrvEventState *) evstate->hb.next;
-	--num_state_prealloc;
-	erts_spin_unlock(&state_prealloc_lock);
+	evstate = drv_ev_state.prealloc_first;
+	drv_ev_state.prealloc_first = (ErtsDrvEventState *) evstate->hb.next;
+	--drv_ev_state.num_prealloc;
+	erts_spin_unlock(&drv_ev_state.prealloc_lock);
     }
     /* XXX: Already valid data if prealloced, could ignore template! */
     *evstate = *((ErtsDrvEventState *) des_tmpl);
@@ -2493,58 +1878,200 @@ static void *drv_ev_state_alloc(void *des_tmpl)
 
 static void drv_ev_state_free(void *des)
 {
-    erts_spin_lock(&state_prealloc_lock);
-    ((ErtsDrvEventState *) des)->hb.next = &state_prealloc_first->hb;
-    state_prealloc_first = (ErtsDrvEventState *) des;
-    ++num_state_prealloc;
-    erts_spin_unlock(&state_prealloc_lock);
+    erts_spin_lock(&drv_ev_state.prealloc_lock);
+    ((ErtsDrvEventState *) des)->hb.next = &drv_ev_state.prealloc_first->hb;
+    drv_ev_state.prealloc_first = (ErtsDrvEventState *) des;
+    ++drv_ev_state.num_prealloc;
+    erts_spin_unlock(&drv_ev_state.prealloc_lock);
 }
 #endif
 
+#define ERTS_MAX_NO_OF_POLL_THREADS ERTS_MAX_NO_OF_SCHEDULERS
+
+static char *
+get_arg(char* rest, char** argv, int* ip)
+{
+    int i = *ip;
+    if (*rest == '\0') {
+	if (argv[i+1] == NULL) {
+	    erts_fprintf(stderr, "too few arguments\n");
+	    erts_usage();
+	}
+        argv[i++] = NULL;
+        rest = argv[i];
+    }
+    argv[i] = NULL;
+    *ip = i;
+    return rest;
+}
+
+static void
+parse_args(int *argc, char **argv, int concurrent_waiters)
+{
+    int i = 0, j;
+    int no_pollsets = 0, no_poll_threads = 0,
+        no_pollsets_percentage = 0,
+        no_poll_threads_percentage = 0;
+    ASSERT(argc && argv);
+    while (i < *argc) {
+	if(argv[i][0] == '-') {
+	    switch (argv[i][1]) {
+            case 'I': {
+                if (strncmp(argv[i]+2, "Ot", 2) == 0) {
+                    char *arg = get_arg(argv[i]+4, argv, &i);
+                    if (sscanf(arg, "%d", &no_poll_threads) != 1 ||
+                        no_poll_threads < 1 ||
+                        ERTS_MAX_NO_OF_POLL_THREADS < no_poll_threads) {
+                        erts_fprintf(stderr,"bad I/O poll threads number: %s\n", arg);
+                        erts_usage();
+                    }
+                } else if (strncmp(argv[i]+2, "Op", 3) == 0) {
+                    char *arg = get_arg(argv[i]+4, argv, &i);
+                    if (sscanf(arg, "%d", &no_pollsets) != 1 ||
+                        no_pollsets < 1) {
+                        erts_fprintf(stderr,"bad I/O pollset number: %s\n", arg);
+                        erts_usage();
+                    }
+                } else if (strncmp(argv[i]+2, "OPt", 4) == 0) {
+                    char *arg = get_arg(argv[i]+5, argv, &i);
+                    if (sscanf(arg, "%d", &no_poll_threads_percentage) != 1 ||
+                        no_poll_threads_percentage < 0 ||
+                        no_poll_threads_percentage > 100) {
+                        erts_fprintf(stderr,"bad I/O poll thread percentage number: %s\n", arg);
+                        erts_usage();
+                    }
+                } else if (strncmp(argv[i]+2, "OPp", 4) == 0) {
+                    char *arg = get_arg(argv[i]+5, argv, &i);
+                    if (sscanf(arg, "%d", &no_pollsets_percentage) != 1 ||
+                        no_pollsets_percentage < 0 ||
+                        no_pollsets_percentage > 100) {
+                        erts_fprintf(stderr,"bad I/O pollset percentage number: %s\n", arg);
+                        erts_usage();
+                    }
+                } else {
+                    break;
+                }
+                break;
+            }
+            case 'K':
+                (void)get_arg(argv[i]+2, argv, &i);
+                break;
+            case '-':
+                goto args_parsed;
+            default:
+                break;
+            }
+        }
+        i++;
+    }
+
+args_parsed:
+
+    if (!concurrent_waiters) {
+        no_pollsets = no_poll_threads;
+        no_pollsets_percentage = 100;
+    }
+
+    if (no_poll_threads == 0) {
+        if (no_poll_threads_percentage == 0)
+            no_poll_threads = 1; /* This is the default */
+        else {
+            no_poll_threads = erts_no_schedulers * no_poll_threads_percentage / 100;
+            if (no_poll_threads < 1)
+                no_poll_threads = 1;
+        }
+    }
+
+    if (no_pollsets == 0) {
+        if (no_pollsets_percentage == 0)
+            no_pollsets = 1; /* This is the default */
+        else {
+            no_pollsets = no_poll_threads * no_pollsets_percentage / 100;
+            if (no_pollsets < 1)
+                no_pollsets = 1;
+        }
+    }
+
+    if (no_poll_threads < no_pollsets) {
+        erts_fprintf(stderr,
+                     "number of IO poll threads has to be greater or equal to "
+                     "the number of \nIO pollsets. Current values are set to: \n"
+                     "  -IOt %d -IOp %d\n",
+                     no_poll_threads, no_pollsets);
+        erts_usage();
+    }
+
+    /* Handled arguments have been marked with NULL. Slide arguments
+       not handled towards the beginning of argv. */
+    for (i = 0, j = 0; i < *argc; i++) {
+	if (argv[i])
+	    argv[j++] = argv[i];
+    }
+    *argc = j;
+
+    erts_no_pollsets = no_pollsets;
+    erts_no_poll_threads = no_poll_threads;
+}
+
 void
-ERTS_CIO_EXPORT(erts_init_check_io)(void)
+erts_init_check_io(int *argc, char **argv)
 {
+    int j, concurrent_waiters, no_poll_threads;
     ERTS_CT_ASSERT((INT_MIN & (ERL_NIF_SELECT_STOP_CALLED |
                                ERL_NIF_SELECT_STOP_SCHEDULED |
                                ERL_NIF_SELECT_INVALID_EVENT |
                                ERL_NIF_SELECT_FAILED)) == 0);
-    erts_atomic_init_nob(&erts_check_io_time, 0);
-    erts_atomic_init_nob(&pollset.in_poll_wait, 0);
-
-    ERTS_CIO_POLL_INIT();
-    pollset.ps = ERTS_CIO_NEW_POLLSET();
-
-    pollset.active_fd.six = 0;
-    pollset.active_fd.eix = 0;
-    erts_atomic32_init_nob(&pollset.active_fd.no, 0);
-    pollset.active_fd.size = ERTS_ACTIVE_FD_INC;
-    pollset.active_fd.array = erts_alloc(ERTS_ALC_T_ACTIVE_FD_ARR,
-					 sizeof(ErtsSysFdType)*ERTS_ACTIVE_FD_INC);
-#ifdef DEBUG
-    {
-	int i;
-	for (i = 0; i < ERTS_ACTIVE_FD_INC; i++)
-	    pollset.active_fd.array[i] = ERTS_SYS_FD_INVALID;
-    }
+
+
+    erts_poll_init(&concurrent_waiters);
+#if ERTS_POLL_USE_FALLBACK
+    erts_poll_init_flbk(NULL);
 #endif
 
+    parse_args(argc, argv, concurrent_waiters);
 
-    init_removed_fd_alloc();
-    pollset.removed_list = NULL;
-    erts_spinlock_init(&pollset.removed_list_lock, "pollset_rm_list", NIL,
-        ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_IO);
-    {
-        int i;
-        for (i=0; i<DRV_EV_STATE_LOCK_CNT; i++) {
-            erts_mtx_init(&drv_ev_state_locks[i].lck, "drv_ev_state", make_small(i),
-                ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_IO);
-        }
+    /* Create the actual pollsets */
+    pollsetv = erts_alloc(ERTS_ALC_T_POLLSET,sizeof(ErtsPollSet *) * erts_no_pollsets);
+
+    for (j=0; j < erts_no_pollsets; j++)
+        pollsetv[j] = erts_poll_create_pollset(j);
+
+#if ERTS_POLL_USE_FALLBACK
+    flbk_pollset = erts_poll_create_pollset_flbk(-1);
+#endif
+
+    no_poll_threads = erts_no_poll_threads;
+#if ERTS_POLL_USE_FALLBACK
+    no_poll_threads++;
+#endif
+
+    psiv = erts_alloc(ERTS_ALC_T_POLLSET, sizeof(ErtsPollThread) * no_poll_threads);
+
+#if ERTS_POLL_USE_FALLBACK
+    psiv[0].pollres_len = ERTS_CHECK_IO_POLL_RES_LEN;
+    psiv[0].pollres = erts_alloc(ERTS_ALC_T_POLLSET,
+        sizeof(ErtsPollResFd) * ERTS_CHECK_IO_POLL_RES_LEN);
+    psiv[0].ps = get_fallback();
+    psiv++;
+#endif
+
+    for (j = 0; j < erts_no_poll_threads; j++) {
+        psiv[j].pollres_len = ERTS_CHECK_IO_POLL_RES_LEN;
+        psiv[j].pollres = erts_alloc(ERTS_ALC_T_POLLSET,
+                                      sizeof(ErtsPollResFd) * ERTS_CHECK_IO_POLL_RES_LEN);
+        psiv[j].ps = pollsetv[j % erts_no_pollsets];
     }
+
+    for (j=0; j < ERTS_CHECK_IO_DRV_EV_STATE_LOCK_CNT; j++) {
+        erts_mtx_init(&drv_ev_state.locks[j].lck, "drv_ev_state", make_small(j),
+                          ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_IO);
+    }
+
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    max_fds = ERTS_CIO_POLL_MAX_FDS();
-    erts_atomic_init_nob(&drv_ev_state_len, 0);
-    drv_ev_state = NULL;
-    erts_mtx_init(&drv_ev_state_grow_lock, "drv_ev_state_grow", NIL,
+    drv_ev_state.max_fds = erts_poll_max_fds();
+    erts_atomic_init_nob(&drv_ev_state.len, 0);
+    drv_ev_state.v = NULL;
+    erts_mtx_init(&drv_ev_state.grow_lock, "drv_ev_state_grow", NIL,
         ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_IO);
 #else
     {
@@ -2553,153 +2080,182 @@ ERTS_CIO_EXPORT(erts_init_check_io)(void)
 	hf.cmp = &drv_ev_state_cmp;
 	hf.alloc = &drv_ev_state_alloc;
 	hf.free = &drv_ev_state_free;
-	num_state_prealloc = 0;
-	state_prealloc_first = NULL;
-	erts_spinlock_init(&state_prealloc_lock,"state_prealloc", NIL,
-        ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_IO);
-
-	safe_hash_init(ERTS_ALC_T_DRV_EV_STATE, &drv_ev_state_tab, "drv_ev_state_tab",
+	drv_ev_state.num_prealloc = 0;
+	drv_ev_state.prealloc_first = NULL;
+	erts_spinlock_init(&drv_ev_state.prealloc_lock, "state_prealloc", NIL,
+                               ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_IO);
+	safe_hash_init(ERTS_ALC_T_DRV_EV_STATE, &drv_ev_state.tab, "drv_ev_state_tab",
             ERTS_LOCK_FLAGS_CATEGORY_IO, DRV_EV_STATE_HTAB_SIZE, hf);
     }
 #endif
 }
 
 int
-ERTS_CIO_EXPORT(erts_check_io_max_files)(void)
+erts_check_io_max_files(void)
 {
 #ifdef  ERTS_SYS_CONTINOUS_FD_NUMBERS
-    return max_fds;
+    return drv_ev_state.max_fds;
 #else
-    return ERTS_POLL_EXPORT(erts_poll_max_fds)();
+    return erts_poll_max_fds();
 #endif
 }
 
 Uint
-ERTS_CIO_EXPORT(erts_check_io_size)(void)
+erts_check_io_size(void)
 {
-    Uint res;
+    Uint res = 0;
     ErtsPollInfo pi;
-    ERTS_CIO_POLL_INFO(pollset.ps, &pi);
-    res = pi.memory_size;
+    int i;
+
+#if ERTS_POLL_USE_FALLBACK
+    erts_poll_info(get_fallback(), &pi);
+    res += pi.memory_size;
+#endif
+
+    for (i = 0; i < erts_no_pollsets; i++) {
+        erts_poll_info(pollsetv[i], &pi);
+        res += pi.memory_size;
+    }
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    res += sizeof(ErtsDrvEventState) * erts_atomic_read_nob(&drv_ev_state_len);
+    res += sizeof(ErtsDrvEventState) * erts_atomic_read_nob(&drv_ev_state.len);
 #else
-    res += safe_hash_table_sz(&drv_ev_state_tab);
+    res += safe_hash_table_sz(&drv_ev_state.tab);
     {
 	SafeHashInfo hi;
-	safe_hash_get_info(&hi, &drv_ev_state_tab);
+	safe_hash_get_info(&hi, &drv_ev_state.tab);
 	res += hi.objs * sizeof(ErtsDrvEventState);
     }
-    erts_spin_lock(&state_prealloc_lock);
-    res += num_state_prealloc * sizeof(ErtsDrvEventState);
-    erts_spin_unlock(&state_prealloc_lock);
+    erts_spin_lock(&drv_ev_state.prealloc_lock);
+    res += drv_ev_state.num_prealloc * sizeof(ErtsDrvEventState);
+    erts_spin_unlock(&drv_ev_state.prealloc_lock);
 #endif
     return res;
 }
 
 Eterm
-ERTS_CIO_EXPORT(erts_check_io_info)(void *proc)
+erts_check_io_info(void *proc)
 {
     Process *p = (Process *) proc;
-    Eterm tags[16], values[16], res;
-    Uint sz, *szp, *hp, **hpp, memory_size;
-    Sint i;
-    ErtsPollInfo pi;
-    erts_aint_t cio_time = erts_atomic_read_acqb(&erts_check_io_time);
-    int active_fds = (int) erts_atomic32_read_acqb(&pollset.active_fd.no);
+    Eterm tags[16], values[16], res, list = NIL;
+    Uint sz, *szp, *hp, **hpp;
+    ErtsPollInfo *piv;
+    Sint i, j = 0, len;
+    int no_pollsets = erts_no_pollsets + ERTS_POLL_USE_FALLBACK;
+    ERTS_CT_ASSERT(ERTS_POLL_USE_FALLBACK == 0 || ERTS_POLL_USE_FALLBACK == 1);
 
-    while (1) {
-	erts_aint_t post_cio_time;
-	int post_active_fds;
+    piv = erts_alloc(ERTS_ALC_T_TMP, sizeof(ErtsPollInfo) * no_pollsets);
 
-	ERTS_CIO_POLL_INFO(pollset.ps, &pi);
+#if ERTS_POLL_USE_FALLBACK
+    erts_poll_info_flbk(get_fallback(), &piv[0]);
+    piv[0].poll_threads = 1;
+    piv[0].active_fds = 0;
+    piv++;
+#endif
 
-	post_cio_time = erts_atomic_read_mb(&erts_check_io_time);
-	post_active_fds = (int) erts_atomic32_read_acqb(&pollset.active_fd.no);
-	if (cio_time == post_cio_time && active_fds == post_active_fds)
-	    break;
-	cio_time = post_cio_time;
-	active_fds = post_active_fds;
+    for (j = 0; j < erts_no_pollsets; j++) {
+        erts_poll_info(pollsetv[j], &piv[j]);
+        piv[j].active_fds = 0;
+        piv[j].poll_threads = erts_no_poll_threads / erts_no_pollsets;
+        if (erts_no_poll_threads % erts_no_pollsets > j)
+            piv[j].poll_threads++;
     }
 
-    memory_size = pi.memory_size;
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    memory_size += sizeof(ErtsDrvEventState) * erts_atomic_read_nob(&drv_ev_state_len);
+    i = 0;
+    erts_mtx_lock(&drv_ev_state.grow_lock);
+    len = erts_atomic_read_nob(&drv_ev_state.len);
+    for (i = 0; i < ERTS_CHECK_IO_DRV_EV_STATE_LOCK_CNT; i++) {
+        erts_mtx_lock(&drv_ev_state.locks[i].lck);
+        for (j = i; j < len; j+=ERTS_CHECK_IO_DRV_EV_STATE_LOCK_CNT) {
+            ErtsDrvEventState *state = get_drv_ev_state(j);
+            int pollsetid = get_pollset_id(j);
+            ASSERT(fd_mtx(j) == &drv_ev_state.locks[i].lck);
+            if (state->flags & ERTS_EV_FLAG_FALLBACK)
+                pollsetid = -1;
+            if (state->driver.select
+                && (state->type == ERTS_EV_TYPE_DRV_SEL)
+                && (is_iotask_active(&state->driver.select->iniotask)
+                    || is_iotask_active(&state->driver.select->outiotask)))
+                piv[pollsetid].active_fds++;
+        }
+        erts_mtx_unlock(&drv_ev_state.locks[i].lck);
+    }
+    erts_mtx_unlock(&drv_ev_state.grow_lock);
+
+    piv[0].memory_size += sizeof(ErtsDrvEventState) * erts_atomic_read_nob(&drv_ev_state.len);
 #else
-    memory_size += safe_hash_table_sz(&drv_ev_state_tab);
+    piv[0].memory_size += safe_hash_table_sz(&drv_ev_state.tab);
     {
-	SafeHashInfo hi;
-	safe_hash_get_info(&hi, &drv_ev_state_tab);
-	memory_size += hi.objs * sizeof(ErtsDrvEventState);
+        SafeHashInfo hi;
+        safe_hash_get_info(&hi, &drv_ev_state.tab);
+        piv[0].memory_size += hi.objs * sizeof(ErtsDrvEventState);
     }
-    erts_spin_lock(&state_prealloc_lock);
-    memory_size += num_state_prealloc * sizeof(ErtsDrvEventState);
-    erts_spin_unlock(&state_prealloc_lock);
+    erts_spin_lock(&drv_ev_state.prealloc_lock);
+    piv[0].memory_size += drv_ev_state.num_prealloc * sizeof(ErtsDrvEventState);
+    erts_spin_unlock(&drv_ev_state.prealloc_lock);
 #endif
 
     hpp = NULL;
     szp = &sz;
     sz = 0;
 
- bld_it:
-    i = 0;
+    piv -= ERTS_POLL_USE_FALLBACK;
 
-    tags[i] = erts_bld_atom(hpp, szp, "name");
-    values[i++] = erts_bld_atom(hpp, szp, "erts_poll");
+ bld_it:
 
-    tags[i] = erts_bld_atom(hpp, szp, "primary");
-    values[i++] = erts_bld_atom(hpp, szp, pi.primary);
+    for (j = no_pollsets-1; j >= 0; j--) {
+        i = 0;
 
-    tags[i] = erts_bld_atom(hpp, szp, "fallback");
-    values[i++] = erts_bld_atom(hpp, szp, pi.fallback ? pi.fallback : "false");
+        tags[i] = erts_bld_atom(hpp, szp, "name");
+        values[i++] = erts_bld_atom(hpp, szp, "erts_poll");
 
-    tags[i] = erts_bld_atom(hpp, szp, "kernel_poll");
-    values[i++] = erts_bld_atom(hpp, szp,
-				pi.kernel_poll ? pi.kernel_poll : "false");
+        tags[i] = erts_bld_atom(hpp, szp, "primary");
+        values[i++] = erts_bld_atom(hpp, szp, piv[j].primary);
 
-    tags[i] = erts_bld_atom(hpp, szp, "memory_size");
-    values[i++] = erts_bld_uint(hpp, szp, memory_size);
+        tags[i] = erts_bld_atom(hpp, szp, "kernel_poll");
+        values[i++] = erts_bld_atom(hpp, szp,
+                                    piv[j].kernel_poll ? piv[j].kernel_poll : "false");
 
-    tags[i] = erts_bld_atom(hpp, szp, "total_poll_set_size");
-    values[i++] = erts_bld_uint(hpp, szp, (Uint) pi.poll_set_size);
+        tags[i] = erts_bld_atom(hpp, szp, "memory_size");
+        values[i++] = erts_bld_uint(hpp, szp, piv[j].memory_size);
 
-    if (pi.fallback) {
-	tags[i] = erts_bld_atom(hpp, szp, "fallback_poll_set_size");
-	values[i++] = erts_bld_uint(hpp, szp, (Uint) pi.fallback_poll_set_size);
-    }
+        tags[i] = erts_bld_atom(hpp, szp, "total_poll_set_size");
+        values[i++] = erts_bld_uint(hpp, szp, piv[j].poll_set_size);
 
-    tags[i] = erts_bld_atom(hpp, szp, "lazy_updates");
-    values[i++] = pi.lazy_updates ? am_true : am_false;
+        tags[i] = erts_bld_atom(hpp, szp, "lazy_updates");
+        values[i++] = piv[j].lazy_updates ? am_true : am_false;
 
-    if (pi.lazy_updates) {
-	tags[i] = erts_bld_atom(hpp, szp, "pending_updates");
-	values[i++] = erts_bld_uint(hpp, szp, (Uint) pi.pending_updates);
-    }
+        tags[i] = erts_bld_atom(hpp, szp, "pending_updates");
+        values[i++] = erts_bld_uint(hpp, szp, piv[j].pending_updates);
 
-    tags[i] = erts_bld_atom(hpp, szp, "batch_updates");
-    values[i++] = pi.batch_updates ? am_true : am_false;
+        tags[i] = erts_bld_atom(hpp, szp, "batch_updates");
+        values[i++] = piv[j].batch_updates ? am_true : am_false;
 
-    tags[i] = erts_bld_atom(hpp, szp, "concurrent_updates");
-    values[i++] = pi.concurrent_updates ? am_true : am_false;
+        tags[i] = erts_bld_atom(hpp, szp, "concurrent_updates");
+        values[i++] = piv[j].concurrent_updates ? am_true : am_false;
 
-    tags[i] = erts_bld_atom(hpp, szp, "max_fds");
-    values[i++] = erts_bld_uint(hpp, szp, (Uint) pi.max_fds);
+        tags[i] = erts_bld_atom(hpp, szp, "fallback");
+        values[i++] = piv[j].is_fallback ? am_true : am_false;
 
-    tags[i] = erts_bld_atom(hpp, szp, "active_fds");
-    values[i++] = erts_bld_uint(hpp, szp, (Uint) active_fds);
+        tags[i] = erts_bld_atom(hpp, szp, "max_fds");
+        values[i++] = erts_bld_uint(hpp, szp, piv[j].max_fds);
 
-#ifdef ERTS_POLL_COUNT_AVOIDED_WAKEUPS
-    tags[i] = erts_bld_atom(hpp, szp, "no_avoided_wakeups");
-    values[i++] = erts_bld_uint(hpp, szp, (Uint) pi.no_avoided_wakeups);
+        tags[i] = erts_bld_atom(hpp, szp, "active_fds");
+        values[i++] = erts_bld_uint(hpp, szp, piv[j].active_fds);
 
-    tags[i] = erts_bld_atom(hpp, szp, "no_avoided_interrupts");
-    values[i++] = erts_bld_uint(hpp, szp, (Uint) pi.no_avoided_interrupts);
+        tags[i] = erts_bld_atom(hpp, szp, "poll_threads");
+        values[i++] = erts_bld_uint(hpp, szp, piv[j].poll_threads);
 
-    tags[i] = erts_bld_atom(hpp, szp, "no_interrupt_timed");
-    values[i++] = erts_bld_uint(hpp, szp, (Uint) pi.no_interrupt_timed);
-#endif
+        res = erts_bld_2tup_list(hpp, szp, i, tags, values);
 
-    res = erts_bld_2tup_list(hpp, szp, i, tags, values);
+        if (!hpp) {
+            *szp += 2;
+        }
+        else {
+            list = CONS(*hpp, res, list);
+            *hpp += 2;
+        }
+    }
 
     if (!hpp) {
 	hp = HAlloc(p, sz);
@@ -2708,386 +2264,442 @@ ERTS_CIO_EXPORT(erts_check_io_info)(void *proc)
 	goto bld_it;
     }
 
-    return res;
+    erts_free(ERTS_ALC_T_TMP, piv);
+
+    return list;
 }
 
 static ERTS_INLINE ErtsPollEvents
-print_events(ErtsPollEvents ev)
+print_events(erts_dsprintf_buf_t *dsbufp, ErtsPollEvents ev)
 {
     int first = 1;
+    if(ev == ERTS_POLL_EV_NONE) {
+        erts_dsprintf(dsbufp, "N/A");
+        return 0;
+    }
     if(ev & ERTS_POLL_EV_IN) {
 	ev &= ~ERTS_POLL_EV_IN;
-	erts_printf("%s%s", first ? "" : "|", "IN");
+	erts_dsprintf(dsbufp, "%s%s", first ? "" : "|", "IN");
 	first = 0;
     }
     if(ev & ERTS_POLL_EV_OUT) {
 	ev &= ~ERTS_POLL_EV_OUT;
-	erts_printf("%s%s", first ? "" : "|", "OUT");
+	erts_dsprintf(dsbufp, "%s%s", first ? "" : "|", "OUT");
 	first = 0;
     }
     /* The following should not appear... */
     if(ev & ERTS_POLL_EV_NVAL) {
-	erts_printf("%s%s", first ? "" : "|", "NVAL");
+	erts_dsprintf(dsbufp, "%s%s", first ? "" : "|", "NVAL");
 	first = 0;
     }
     if(ev & ERTS_POLL_EV_ERR) {
-	erts_printf("%s%s", first ? "" : "|", "ERR");
+	erts_dsprintf(dsbufp, "%s%s", first ? "" : "|", "ERR");
 	first = 0;
     }
     if (ev)
-	erts_printf("%s0x%b32x", first ? "" : "|", (Uint32) ev);
+	erts_dsprintf(dsbufp, "%s0x%b32x", first ? "" : "|", (Uint32) ev);
     return ev;
 }
 
+static ERTS_INLINE void
+print_flags(erts_dsprintf_buf_t *dsbufp, EventStateFlags f)
+{
+    const char* delim = "";
+    if(f & ERTS_EV_FLAG_USED) {
+	erts_dsprintf(dsbufp, "%s","USED");
+	delim = "|";
+    }
+    if(f & ERTS_EV_FLAG_FALLBACK) {
+	erts_dsprintf(dsbufp, "%s%s", delim, "FLBK");
+        delim = "|";
+    }
+}
+
+#ifdef DEBUG_PRINT_MODE
+
+static ERTS_INLINE char *
+drvmode2str(int mode) {
+    switch (mode) {
+    case ERL_DRV_READ|ERL_DRV_USE: return "READ|USE";
+    case ERL_DRV_WRITE|ERL_DRV_USE: return "WRITE|USE";
+    case ERL_DRV_READ|ERL_DRV_WRITE|ERL_DRV_USE: return "READ|WRITE|USE";
+    case ERL_DRV_USE: return "USE";
+    case ERL_DRV_READ: return "READ";
+    case ERL_DRV_WRITE: return "WRITE";
+    case ERL_DRV_READ|ERL_DRV_WRITE: return "READ|WRITE";
+    default: return "UNKNOWN";
+    }
+}
+
+static ERTS_INLINE char *
+nifmode2str(enum ErlNifSelectFlags mode) {
+    switch (mode) {
+    case ERL_NIF_SELECT_READ: return "READ";
+    case ERL_NIF_SELECT_WRITE: return "WRITE";
+    case ERL_NIF_SELECT_STOP: return "STOP";
+    default: return "UNKNOWN";
+    }
+}
+
+#endif
+
 typedef struct {
     int used_fds;
     int num_errors;
     int no_driver_select_structs;
-    int no_driver_event_structs;
+    int no_enif_select_structs;
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
     int internal_fds;
     ErtsPollEvents *epep;
 #endif
 } IterDebugCounters;
 
-static void doit_erts_check_io_debug(void *vstate, void *vcounters)
+static int erts_debug_print_checkio_state(erts_dsprintf_buf_t *dsbufp,
+                                          ErtsDrvEventState *state,
+                                          ErtsPollEvents ep_events,
+                                          int internal)
 {
-    ErtsDrvEventState *state = (ErtsDrvEventState *) vstate;
-    IterDebugCounters *counters = (IterDebugCounters *) vcounters;
-    ErtsPollEvents cio_events = state->events;
-    ErtsSysFdType fd = state->fd;
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    int internal = 0;
-    ErtsPollEvents ep_events = counters->epep[(int) fd];
-#endif
-    int err = 0;
-
 #if defined(HAVE_FSTAT) && !defined(NO_FSTAT_ON_SYS_FD_TYPE)
     struct stat stat_buf;
 #endif
-
-    if (state->driver.select)
-	counters->no_driver_select_structs++;
-#if ERTS_CIO_HAVE_DRV_EVENT
-    if (state->driver.event)
-	counters->no_driver_event_structs++;
-#endif
-
+    ErtsSysFdType fd = state->fd;
+    ErtsPollEvents cio_events = state->events;
+    int err = 0;
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    if (state->events || ep_events) {
-	if (ep_events & ERTS_POLL_EV_NVAL) {
-	    ep_events &= ~ERTS_POLL_EV_NVAL;
-	    internal = 1;
-	    counters->internal_fds++;
-	}
-	else
-	    counters->used_fds++;
-#else
-    if (state->events) {
-	counters->used_fds++;
+    ErtsPollEvents aio_events = state->active_events;
 #endif
-	
-	erts_printf("fd=%d ", (int) fd);
-	
+    erts_dsprintf(dsbufp, "pollset=%d fd=%d ",
+                state->flags & ERTS_EV_FLAG_FALLBACK ? -1 : get_pollset_id(fd), (int) fd);
+
 #if defined(HAVE_FSTAT) && !defined(NO_FSTAT_ON_SYS_FD_TYPE)
-	if (fstat((int) fd, &stat_buf) < 0)
-	    erts_printf("type=unknown ");
-	else {
-	    erts_printf("type=");
+    if (fstat((int) fd, &stat_buf) < 0)
+        erts_dsprintf(dsbufp, "type=unknown ");
+    else {
+        erts_dsprintf(dsbufp, "type=");
 #ifdef S_ISSOCK
-	    if (S_ISSOCK(stat_buf.st_mode))
-		erts_printf("sock ");
-	    else
+        if (S_ISSOCK(stat_buf.st_mode))
+            erts_dsprintf(dsbufp, "sock ");
+        else
 #endif
 #ifdef S_ISFIFO
 	    if (S_ISFIFO(stat_buf.st_mode))
-		erts_printf("fifo ");
+		erts_dsprintf(dsbufp, "fifo ");
 	    else
 #endif
 #ifdef S_ISCHR
-	    if (S_ISCHR(stat_buf.st_mode))
-		erts_printf("chr ");
-	    else
+                if (S_ISCHR(stat_buf.st_mode))
+                    erts_dsprintf(dsbufp, "chr ");
+                else
 #endif
 #ifdef S_ISDIR
-	    if (S_ISDIR(stat_buf.st_mode))
-		erts_printf("dir ");
-	    else
+                    if (S_ISDIR(stat_buf.st_mode))
+                        erts_dsprintf(dsbufp, "dir ");
+                    else
 #endif
 #ifdef S_ISBLK
-	    if (S_ISBLK(stat_buf.st_mode))
-		erts_printf("blk ");
-	    else
+                        if (S_ISBLK(stat_buf.st_mode))
+                            erts_dsprintf(dsbufp, "blk ");
+                        else
 #endif
 #ifdef S_ISREG
-	    if (S_ISREG(stat_buf.st_mode))
-		erts_printf("reg ");
-	    else
+                            if (S_ISREG(stat_buf.st_mode))
+                                erts_dsprintf(dsbufp, "reg ");
+                            else
 #endif
 #ifdef S_ISLNK
-	    if (S_ISLNK(stat_buf.st_mode))
-		erts_printf("lnk ");
-	    else
+                                if (S_ISLNK(stat_buf.st_mode))
+                                    erts_dsprintf(dsbufp, "lnk ");
+                                else
 #endif
 #ifdef S_ISDOOR
-	    if (S_ISDOOR(stat_buf.st_mode))
-		erts_printf("door ");
-	    else
+                                    if (S_ISDOOR(stat_buf.st_mode))
+                                        erts_dsprintf(dsbufp, "door ");
+                                    else
 #endif
 #ifdef S_ISWHT
-	    if (S_ISWHT(stat_buf.st_mode))
-		erts_printf("wht ");
-	    else
+                                        if (S_ISWHT(stat_buf.st_mode))
+                                            erts_dsprintf(dsbufp, "wht ");
+                                        else
 #endif
 #ifdef S_ISXATTR
-	    if (S_ISXATTR(stat_buf.st_mode))
-		erts_printf("xattr ");
-	    else
+                                            if (S_ISXATTR(stat_buf.st_mode))
+                                                erts_dsprintf(dsbufp, "xattr ");
+                                            else
 #endif
-		erts_printf("unknown ");
-	}
+                                                erts_dsprintf(dsbufp, "unknown ");
+    }
 #else
-	erts_printf("type=unknown ");
+    erts_dsprintf(dsbufp, "type=unknown ");
 #endif
 
-	if (state->type == ERTS_EV_TYPE_DRV_SEL) {
-	    erts_printf("driver_select ");
-	    
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-	    if (internal) {
-		erts_printf("internal ");
-		err = 1;		    
-	    }
-	    
-	    if (cio_events == ep_events) {
-		erts_printf("ev=");
-		if (print_events(cio_events) != 0)
-		    err = 1;
-	    }
-	    else {
-		err = 1;
-		erts_printf("cio_ev=");
-		print_events(cio_events);
-		erts_printf(" ep_ev=");
-		print_events(ep_events);
-	    }
-#else
-	    if (print_events(cio_events) != 0)
-		err = 1;
-#endif
-	    erts_printf(" ");
-	    if (cio_events & ERTS_POLL_EV_IN) {
-		Eterm id = state->driver.select->inport;
-		if (is_nil(id)) {
-		    erts_printf("inport=none inname=none indrv=none ");
-		    err = 1;
-		}
-		else {
-		    ErtsPortNames *pnp = erts_get_port_names(id, ERTS_INVALID_ERL_DRV_PORT);
-		    erts_printf(" inport=%T inname=%s indrv=%s ",
-				id,
-				pnp->name ? pnp->name : "unknown",
-				(pnp->driver_name
-				 ? pnp->driver_name
-				 : "unknown"));
-		    erts_free_port_names(pnp);
-		}
-	    }
-	    if (cio_events & ERTS_POLL_EV_OUT) {
-		Eterm id = state->driver.select->outport;
-		if (is_nil(id)) {
-		    erts_printf("outport=none outname=none outdrv=none ");
-		    err = 1;
-		}
-		else {
-		    ErtsPortNames *pnp = erts_get_port_names(id, ERTS_INVALID_ERL_DRV_PORT);
-		    erts_printf(" outport=%T outname=%s outdrv=%s ",
-				id,
-				pnp->name ? pnp->name : "unknown",
-				(pnp->driver_name
-				 ? pnp->driver_name
-				 : "unknown"));
-		    erts_free_port_names(pnp);
-		}
-	    }
-	}
-        else if (state->type == ERTS_EV_TYPE_NIF) {
-            ErtsResource* r;
-            erts_printf("enif_select ");
+    if (state->type == ERTS_EV_TYPE_DRV_SEL) {
+        erts_dsprintf(dsbufp, "driver_select ");
 
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-            if (internal) {
-                erts_printf("internal ");
-                err = 1;
-            }
-
+        if (internal) {
+            erts_dsprintf(dsbufp, "internal ");
+            err = 1;
+        }
+        if (aio_events == cio_events) {
             if (cio_events == ep_events) {
-                erts_printf("ev=");
-                if (print_events(cio_events) != 0)
+                erts_dsprintf(dsbufp, "ev=");
+                if (print_events(dsbufp, cio_events) != 0)
                     err = 1;
             }
             else {
+                ErtsPollEvents ev = cio_events;
+                if (ev != ep_events && ep_events != ERTS_POLL_EV_NONE)
+                    err = 1;
+                erts_dsprintf(dsbufp, "cio_ev=");
+                print_events(dsbufp, cio_events);
+                erts_dsprintf(dsbufp, " ep_ev=");
+                print_events(dsbufp, ep_events);
+            }
+        } else {
+            erts_dsprintf(dsbufp, "cio_ev=");
+            print_events(dsbufp, cio_events);
+            erts_dsprintf(dsbufp, " aio_ev=");
+            print_events(dsbufp, aio_events);
+            if ((aio_events != ep_events && ep_events != ERTS_POLL_EV_NONE) ||
+                (aio_events != 0 && ep_events == ERTS_POLL_EV_NONE)) {
+                erts_dsprintf(dsbufp, " ep_ev=");
+                print_events(dsbufp, ep_events);
                 err = 1;
-                erts_printf("cio_ev=");
-                print_events(cio_events);
-                erts_printf(" ep_ev=");
-                print_events(ep_events);
             }
+        }
 #else
-            if (print_events(cio_events) != 0)
+        if (print_events(dsbufp, cio_events) != 0)
+            err = 1;
+#endif
+        erts_dsprintf(dsbufp, " ");
+        if (cio_events & ERTS_POLL_EV_IN) {
+            Eterm id = state->driver.select->inport;
+            if (is_nil(id)) {
+                erts_dsprintf(dsbufp, "inport=none inname=none indrv=none ");
                 err = 1;
-#endif
-            erts_printf(" inpid=%T dd_cnt=%b32d", state->driver.nif->in.pid,
-                        state->driver.nif->in.ddeselect_cnt);
-            erts_printf(" outpid=%T dd_cnt=%b32d", state->driver.nif->out.pid,
-                        state->driver.nif->out.ddeselect_cnt);
-            r = state->driver.stop.resource;
-            erts_printf(" resource=%p(%T:%T)", r, r->type->module, r->type->name);
+            }
+            else {
+                ErtsPortNames *pnp = erts_get_port_names(id, ERTS_INVALID_ERL_DRV_PORT);
+                erts_dsprintf(dsbufp, " inport=%T inname=%s indrv=%s ",
+                            id,
+                            pnp->name ? pnp->name : "unknown",
+                            (pnp->driver_name
+                             ? pnp->driver_name
+                             : "unknown"));
+                erts_free_port_names(pnp);
+            }
         }
-#if ERTS_CIO_HAVE_DRV_EVENT
-	else if (state->type == ERTS_EV_TYPE_DRV_EV) {
-	    Eterm id;
-	    erts_printf("driver_event ");
+        if (cio_events & ERTS_POLL_EV_OUT) {
+            Eterm id = state->driver.select->outport;
+            if (is_nil(id)) {
+                erts_dsprintf(dsbufp, "outport=none outname=none outdrv=none ");
+                err = 1;
+            }
+            else {
+                ErtsPortNames *pnp = erts_get_port_names(id, ERTS_INVALID_ERL_DRV_PORT);
+                erts_dsprintf(dsbufp, " outport=%T outname=%s outdrv=%s ",
+                            id,
+                            pnp->name ? pnp->name : "unknown",
+                            (pnp->driver_name
+                             ? pnp->driver_name
+                             : "unknown"));
+                erts_free_port_names(pnp);
+            }
+        }
+    }
+    else if (state->type == ERTS_EV_TYPE_NIF) {
+        ErtsResource* r;
+        erts_dsprintf(dsbufp, "enif_select ");
+
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-	    if (internal) {
-		erts_printf("internal ");
-		err = 1;		    
-	    }
-	    if (cio_events == ep_events) {
-		erts_printf("ev=0x%b32x", (Uint32) cio_events);
-	    }
-	    else {
-		err = 1;
-		erts_printf("cio_ev=0x%b32x", (Uint32) cio_events);
-		erts_printf(" ep_ev=0x%b32x", (Uint32) ep_events);
-	    }
+        if (internal) {
+            erts_dsprintf(dsbufp, "internal ");
+            err = 1;
+        }
+
+        if (cio_events == ep_events) {
+            erts_dsprintf(dsbufp, "ev=");
+            if (print_events(dsbufp, cio_events) != 0)
+                err = 1;
+        }
+        else {
+            err = 1;
+            erts_dsprintf(dsbufp, "cio_ev=");
+            print_events(dsbufp, cio_events);
+            erts_dsprintf(dsbufp, " ep_ev=");
+            print_events(dsbufp, ep_events);
+        }
 #else
-	    erts_printf("ev=0x%b32x", (Uint32) cio_events);
+        if (print_events(dsbufp, cio_events) != 0)
+            err = 1;
 #endif
-	    id = state->driver.event->port;
-	    if (is_nil(id)) {
-		erts_printf(" port=none name=none drv=none ");
-		err = 1;
-	    }
-	    else {
-		ErtsPortNames *pnp = erts_get_port_names(id, ERTS_INVALID_ERL_DRV_PORT);
-		erts_printf(" port=%T name=%s drv=%s ",
-			    id,
-			    pnp->name ? pnp->name : "unknown",
-			    (pnp->driver_name
-			     ? pnp->driver_name
-			     : "unknown"));
-		erts_free_port_names(pnp);
-	    }
-	}
+        erts_dsprintf(dsbufp, " inpid=%T", state->driver.nif->in.pid);
+        erts_dsprintf(dsbufp, " outpid=%T", state->driver.nif->out.pid);
+        r = state->driver.stop.resource;
+        erts_dsprintf(dsbufp, " resource=%p(%T:%T)", r, r->type->module, r->type->name);
+    }
+#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
+    else if (internal) {
+        erts_dsprintf(dsbufp, "internal ");
+        if (cio_events) {
+            err = 1;
+            erts_dsprintf(dsbufp, "cio_ev=");
+            print_events(dsbufp, cio_events);
+        }
+        if (ep_events) {
+            erts_dsprintf(dsbufp, "ep_ev=");
+            print_events(dsbufp, ep_events);
+        }
+    }
 #endif
+    else {
+        err = 1;
+        erts_dsprintf(dsbufp, "control_type=%d ", (int)state->type);
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-	else if (internal) {
-	    erts_printf("internal ");
-	    if (cio_events) {
-		err = 1;
-		erts_printf("cio_ev=");
-		print_events(cio_events);
-	    }
-	    if (ep_events) {
-		erts_printf("ep_ev=");
-		print_events(ep_events);
-	    }
-	}
+        if (cio_events == ep_events) {
+            erts_dsprintf(dsbufp, "ev=");
+            print_events(dsbufp, cio_events);
+        }
+        else {
+            erts_dsprintf(dsbufp, "cio_ev="); print_events(dsbufp, cio_events);
+            erts_dsprintf(dsbufp, " ep_ev="); print_events(dsbufp, ep_events);
+        }
+#else
+        erts_dsprintf(dsbufp, "ev=0x%b32x", (Uint32) cio_events);
 #endif
-	else {
-	    err = 1;
-	    erts_printf("control_type=%d ", (int)state->type);
+    }
+
+    erts_dsprintf(dsbufp, " flags="); print_flags(dsbufp, state->flags);
+    if (err) {
+        erts_dsprintf(dsbufp, " ERROR");
+    }
+    erts_dsprintf(dsbufp, "\r\n");
+    return err;
+}
+
+static void doit_erts_check_io_debug(void *vstate, void *vcounters,
+                                     erts_dsprintf_buf_t *dsbufp)
+{
+    ErtsDrvEventState *state = (ErtsDrvEventState *) vstate;
+    IterDebugCounters *counters = (IterDebugCounters *) vcounters;
+    int internal = 0;
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-	    if (cio_events == ep_events) {
-                erts_printf("ev=");
-                print_events(cio_events);
-	    }
-	    else {
-		erts_printf("cio_ev="); print_events(cio_events);
-		erts_printf(" ep_ev="); print_events(ep_events);
-	    }
+    ErtsSysFdType fd = state->fd;
+    ErtsPollEvents ep_events = counters->epep[(int) fd];
 #else
-	    erts_printf("ev=0x%b32x", (Uint32) cio_events);
+    ErtsPollEvents ep_events = ERTS_POLL_EV_NONE;
 #endif
+
+    if (state->driver.select) {
+	counters->no_driver_select_structs++;
+        ASSERT(state->events || (ep_events != 0 && ep_events != ERTS_POLL_EV_NONE));
+    }
+    if (state->driver.nif) {
+        counters->no_enif_select_structs++;
+        ASSERT(state->events || (ep_events != 0 && ep_events != ERTS_POLL_EV_NONE));
+    }
+
+#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
+    if (state->events || (ep_events != 0 && ep_events != ERTS_POLL_EV_NONE)) {
+	if (ep_events & ERTS_POLL_EV_NVAL) {
+	    ep_events &= ~ERTS_POLL_EV_NVAL;
+	    internal = 1;
+	    counters->internal_fds++;
 	}
-	
-	if (err) {
+	else
+	    counters->used_fds++;
+#else
+    if (state->events) {
+	counters->used_fds++;
+#endif
+	if (erts_debug_print_checkio_state(dsbufp, state, ep_events, internal)) {
 	    counters->num_errors++;
-	    erts_printf(" ERROR");
 	}
-	erts_printf("\n");
     }
 }
-    
+
+/* ciodpi can be NULL when called from etp-commands */
 int
-ERTS_CIO_EXPORT(erts_check_io_debug)(ErtsCheckIoDebugInfo *ciodip)
+erts_check_io_debug(ErtsCheckIoDebugInfo *ciodip)
 {
+    erts_dsprintf_buf_t *dsbufp = erts_create_logger_dsbuf();
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    int fd, len;
+    int fd, len, i;
 #endif
-    IterDebugCounters counters;
+    IterDebugCounters counters = {0};
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
     ErtsDrvEventState null_des;
 
     null_des.driver.select = NULL;
-#if ERTS_CIO_HAVE_DRV_EVENT
-    null_des.driver.event = NULL;
-#endif
+    null_des.driver.nif = NULL;
     null_des.driver.stop.drv_ptr = NULL;
     null_des.events = 0;
-    null_des.remove_cnt = 0;
     null_des.type = ERTS_EV_TYPE_NONE;
+    null_des.flags = 0;
+
+    counters.epep = erts_alloc(ERTS_ALC_T_TMP,
+                               sizeof(ErtsPollEvents)*drv_ev_state.max_fds);
 #endif
 
-    erts_printf("--- fds in pollset --------------------------------------\n");
 
 #if defined(ERTS_ENABLE_LOCK_CHECK)
     erts_lc_check_exact(NULL, 0); /* No locks should be locked */
 #endif
 
-    erts_thr_progress_block(); /* stop the world to avoid messy locking */
+    if (ciodip)
+        erts_thr_progress_block(); /* stop the world to avoid messy locking */
 
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    counters.epep = erts_alloc(ERTS_ALC_T_TMP, sizeof(ErtsPollEvents)*max_fds);
-    ERTS_POLL_EXPORT(erts_poll_get_selected_events)(pollset.ps, counters.epep, max_fds);
-    counters.internal_fds = 0;
-#endif
-    counters.used_fds = 0;
-    counters.num_errors = 0;
-    counters.no_driver_select_structs = 0;
-    counters.no_driver_event_structs = 0;
+    len = erts_atomic_read_nob(&drv_ev_state.len);
 
-#ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    len = erts_atomic_read_nob(&drv_ev_state_len);
+#if ERTS_POLL_USE_FALLBACK
+    erts_dsprintf(dsbufp, "--- fds in flbk pollset ---------------------------------\n");
+    erts_poll_get_selected_events_flbk(get_fallback(), counters.epep,
+                                       drv_ev_state.max_fds);
     for (fd = 0; fd < len; fd++) {
-	doit_erts_check_io_debug((void *) &drv_ev_state[fd], (void *) &counters);
+        if (drv_ev_state.v[fd].flags & ERTS_EV_FLAG_FALLBACK)
+            doit_erts_check_io_debug(&drv_ev_state.v[fd], &counters, dsbufp);
+    }
+#endif
+    erts_dsprintf(dsbufp, "--- fds in pollset --------------------------------------\n");
+
+    for (i = 0; i < erts_no_pollsets; i++) {
+        erts_poll_get_selected_events(pollsetv[i],
+                                      counters.epep,
+                                      drv_ev_state.max_fds);
+        for (fd = 0; fd < len; fd++) {
+            if (!(drv_ev_state.v[fd].flags & ERTS_EV_FLAG_FALLBACK)
+                && get_pollset_id(fd) == i)
+                doit_erts_check_io_debug(&drv_ev_state.v[fd], &counters, dsbufp);
+        }
     }
-    for ( ; fd < max_fds; fd++) {
-	null_des.fd = fd;
-	doit_erts_check_io_debug((void *) &null_des, (void *) &counters);
+    for (fd = len ; fd < drv_ev_state.max_fds; fd++) {
+        null_des.fd = fd;
+        doit_erts_check_io_debug(&null_des, &counters, dsbufp);
     }
 #else
-    safe_hash_for_each(&drv_ev_state_tab, &doit_erts_check_io_debug, (void *) &counters);
+    safe_hash_for_each(&drv_ev_state.tab, &doit_erts_check_io_debug,
+                       &counters, dsbufp);
 #endif
 
-    erts_thr_progress_unblock();
+    if (ciodip)
+        erts_thr_progress_unblock();
 
-    ciodip->no_used_fds = counters.used_fds;
-    ciodip->no_driver_select_structs = counters.no_driver_select_structs;
-    ciodip->no_driver_event_structs = counters.no_driver_event_structs;
+    if (ciodip) {
+        ciodip->no_used_fds = counters.used_fds;
+        ciodip->no_driver_select_structs = counters.no_driver_select_structs;
+        ciodip->no_enif_select_structs = counters.no_enif_select_structs;
+    }
 
-    erts_printf("\n");
-    erts_printf("used fds=%d\n", counters.used_fds);
-    erts_printf("Number of driver_select() structures=%d\n", counters.no_driver_select_structs);
-#if ERTS_CIO_HAVE_DRV_EVENT
-    erts_printf("Number of driver_event() structures=%d\n", counters.no_driver_event_structs);
-#endif
+    erts_dsprintf(dsbufp, "\n");
+    erts_dsprintf(dsbufp, "used fds=%d\n", counters.used_fds);
+    erts_dsprintf(dsbufp, "Number of driver_select() structures=%d\n", counters.no_driver_select_structs);
+    erts_dsprintf(dsbufp, "Number of enif_select() structures=%d\n", counters.no_enif_select_structs);
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    erts_printf("internal fds=%d\n", counters.internal_fds);
+    erts_dsprintf(dsbufp, "internal fds=%d\n", counters.internal_fds);
 #endif
-    erts_printf("---------------------------------------------------------\n");
-    fflush(stdout);
+    erts_dsprintf(dsbufp, "---------------------------------------------------------\n");
+    erts_send_error_to_logger_nogl(dsbufp);
 #ifdef ERTS_SYS_CONTINOUS_FD_NUMBERS
     erts_free(ERTS_ALC_T_TMP, (void *) counters.epep);
 #endif
@@ -3096,11 +2708,19 @@ ERTS_CIO_EXPORT(erts_check_io_debug)(ErtsCheckIoDebugInfo *ciodip)
 }
 
 #ifdef ERTS_ENABLE_LOCK_COUNT
-void ERTS_CIO_EXPORT(erts_lcnt_update_cio_locks)(int enable) {
+void erts_lcnt_update_cio_locks(int enable) {
+    int i;
 #ifndef ERTS_SYS_CONTINOUS_FD_NUMBERS
-    erts_lcnt_enable_hash_lock_count(&drv_ev_state_tab, ERTS_LOCK_FLAGS_CATEGORY_IO, enable);
+    erts_lcnt_enable_hash_lock_count(&drv_ev_state.tab, ERTS_LOCK_FLAGS_CATEGORY_IO, enable);
 #else
     (void)enable;
 #endif
+
+#if ERTS_POLL_USE_FALLBACK
+    erts_lcnt_enable_pollset_lock_count_flbk(get_fallback(), enable);
+#endif
+
+    for (i = 0; i < erts_no_pollsets; i++)
+        erts_lcnt_enable_pollset_lock_count(pollsetv[i], enable);
 }
 #endif /* ERTS_ENABLE_LOCK_COUNT */
diff --git a/erts/emulator/sys/common/erl_check_io.h b/erts/emulator/sys/common/erl_check_io.h
index 777942a473..443ef1264c 100644
--- a/erts/emulator/sys/common/erl_check_io.h
+++ b/erts/emulator/sys/common/erl_check_io.h
@@ -18,10 +18,11 @@
  * %CopyrightEnd%
  */
 
-/*
- * Description:	Check I/O
+/**
+ * @description Check I/O, a cross platform IO polling framework for ERTS
  *
- * Author: 	Rickard Green
+ * @author Rickard Green
+ * @author Lukas Larsson
  */
 
 #ifndef ERL_CHECK_IO_H__
@@ -30,72 +31,79 @@
 #include "sys.h"
 #include "erl_sys_driver.h"
 
-#ifdef ERTS_ENABLE_KERNEL_POLL
-
-int driver_select_kp(ErlDrvPort, ErlDrvEvent, int, int);
-int driver_select_nkp(ErlDrvPort, ErlDrvEvent, int, int);
-int enif_select_kp(ErlNifEnv*, ErlNifEvent, enum ErlNifSelectFlags, void*, const ErlNifPid*, Eterm);
-int enif_select_nkp(ErlNifEnv*, ErlNifEvent, enum ErlNifSelectFlags, void*, const ErlNifPid*, Eterm);
-int driver_event_kp(ErlDrvPort, ErlDrvEvent, ErlDrvEventData);
-int driver_event_nkp(ErlDrvPort, ErlDrvEvent, ErlDrvEventData);
-Uint erts_check_io_size_kp(void);
-Uint erts_check_io_size_nkp(void);
-Eterm erts_check_io_info_kp(void *);
-Eterm erts_check_io_info_nkp(void *);
-int erts_check_io_max_files_kp(void);
-int erts_check_io_max_files_nkp(void);
-void erts_check_io_interrupt_kp(int);
-void erts_check_io_interrupt_nkp(int);
-void erts_check_io_interrupt_timed_kp(int, ErtsMonotonicTime);
-void erts_check_io_interrupt_timed_nkp(int, ErtsMonotonicTime);
-void erts_check_io_kp(int);
-void erts_check_io_nkp(int);
-void erts_init_check_io_kp(void);
-void erts_init_check_io_nkp(void);
-int erts_check_io_debug_kp(ErtsCheckIoDebugInfo *);
-int erts_check_io_debug_nkp(ErtsCheckIoDebugInfo *);
-
-#ifdef ERTS_ENABLE_LOCK_COUNT
-void erts_lcnt_update_cio_locks_kp(int enable);
-void erts_lcnt_update_cio_locks_nkp(int enable);
-#endif
-
-#else /* !ERTS_ENABLE_KERNEL_POLL */
+/** @brief a structure that is used by each polling thread */
+struct erts_poll_thread;
 
+/**
+ * Get the memory size of the check io framework
+ */
 Uint erts_check_io_size(void);
-Eterm erts_check_io_info(void *);
+/**
+ * Returns an Eterm with information about all the pollsets active at the
+ * moment.
+ *
+ * @param proc the Process* to allocate the result on. It is passed as
+ *  void * because of header include problems.
+ */
+Eterm erts_check_io_info(void *proc);
+/**
+ * Should be called when a port IO task has been executed in order to re-enable
+ * or clear the information about the fd.
+ *
+ * @param type The type of event that has been completed.
+ * @param handle The port task handle of the event.
+ * @param reset A function pointer to be called when the port task handle
+ *  should be reset.
+ */
+void erts_io_notify_port_task_executed(ErtsPortTaskType type,
+                                       ErtsPortTaskHandle *handle,
+                                       void (*reset)(ErtsPortTaskHandle *));
+/**
+ * Returns the maximum number of fds that the check io framework can handle.
+ */
 int erts_check_io_max_files(void);
-void erts_check_io_interrupt(int);
-void erts_check_io_interrupt_timed(int, ErtsMonotonicTime);
-void erts_check_io(int);
-void erts_init_check_io(void);
-
+/**
+ * Called by any thread that should check for new IO events. This function will
+ * not return unless erts_check_io_interrupt(pt, 1) is called by another thread.
+ *
+ * @param pt the poll thread structure to use.
+ */
+void erts_check_io(struct erts_poll_thread *pt);
+/**
+ * Initialize the check io framework. This function will parse the arguments
+ * and delete any entries that it is interested in.
+ *
+ * @param argc the number of arguments
+ * @param argv an array with the arguments
+ */
+void erts_init_check_io(int *argc, char **argv);
+/**
+ * Interrupt the poll thread so that it can execute other code.
+ *
+ * Should be called with set = 0 by the waiting thread before calling
+ * erts_check_io.
+ *
+ * @param pt the poll thread to wake
+ * @param set whether to set or clear the interrupt flag
+ */
+void erts_check_io_interrupt(struct erts_poll_thread *pt, int set);
+/**
+ * Create a new poll thread structure that is associated with the number no.
+ * It is the callers responsibility that no is unique.
+ */
+struct erts_poll_thread* erts_create_pollset_thread(int no);
 #ifdef ERTS_ENABLE_LOCK_COUNT
+/**
+ * Toggle lock counting on all check io locks
+ */
 void erts_lcnt_update_cio_locks(int enable);
 #endif
 
-#endif
-
-extern erts_atomic_t erts_check_io_time;
-
 typedef struct {
     ErtsPortTaskHandle task;
-    erts_atomic_t executed_time;
+    ErtsSysFdType fd;
 } ErtsIoTask;
 
-ERTS_GLB_INLINE void erts_io_notify_port_task_executed(ErtsPortTaskHandle *pthp);
-
-#if ERTS_GLB_INLINE_INCL_FUNC_DEF
-
-ERTS_GLB_INLINE void
-erts_io_notify_port_task_executed(ErtsPortTaskHandle *pthp)
-{
-    ErtsIoTask *itp = (ErtsIoTask *) (((char *) pthp) - offsetof(ErtsIoTask, task));
-    erts_aint_t ci_time = erts_atomic_read_acqb(&erts_check_io_time);
-    erts_atomic_set_relb(&itp->executed_time, ci_time);
-}
-
-#endif
 
 #endif /*  ERL_CHECK_IO_H__ */
 
@@ -103,6 +111,16 @@ erts_io_notify_port_task_executed(ErtsPortTaskHandle *pthp)
 #define ERL_CHECK_IO_INTERNAL__
 #endif
 
+#define ERTS_CHECK_IO_DRV_EV_STATE_LOCK_CNT 128
+
+/* Controls how many pollsets to allocate. Fd's are hashed into
+   each pollset based on the FD. When doing non-concurrent updates
+   there will be one pollset per thread.
+*/
+extern int erts_no_pollsets;
+extern int erts_no_poll_threads;
+
+
 #ifndef ERL_CHECK_IO_INTERNAL__
 #define ERL_CHECK_IO_INTERNAL__
 #include "erl_poll.h"
@@ -115,24 +133,8 @@ erts_io_notify_port_task_executed(ErtsPortTaskHandle *pthp)
  */
 #  define ERTS_CIO_DEFER_ACTIVE_EVENTS 1
 #else
-#  define ERTS_CIO_DEFER_ACTIVE_EVENTS 0
-#endif
-
-/*
- * ErtsDrvEventDataState is used by driver_event() which is almost never
- * used. We allocate ErtsDrvEventDataState separate since we dont wan't
- * the size of ErtsDrvEventState to increase due to driver_event()
- * information.
- */
-typedef struct {
-    Eterm port;
-    ErlDrvEventData data;
-    ErtsPollEvents removed_events;
-#if ERTS_CIO_DEFER_ACTIVE_EVENTS
-    ErtsPollEvents deferred_events;
+#  define ERTS_CIO_DEFER_ACTIVE_EVENTS 1
 #endif
-    ErtsIoTask iotask;
-} ErtsDrvEventDataState;
 
 typedef struct {
     Eterm inport;
diff --git a/erts/emulator/sys/common/erl_poll.c b/erts/emulator/sys/common/erl_poll.c
index 7d26839b0f..30a595c17a 100644
--- a/erts/emulator/sys/common/erl_poll.c
+++ b/erts/emulator/sys/common/erl_poll.c
@@ -18,9 +18,8 @@
  * %CopyrightEnd%
  */
 
-/*
- * Description:	Poll interface suitable for ERTS with or without
- *              SMP support.
+/**
+ * @description Poll interface suitable for ERTS
  *
  *		The interface is currently implemented using:
  *		- select
@@ -29,12 +28,36 @@
  *              - epoll with poll or select as fallback
  *              - kqueue with poll or select as fallback
  *
- *		Some time in the future it will also be
- *		implemented using Solaris ports.
  *
+ * @author Rickard Green
+ * @author Lukas Larsson
+ *
+ * There are two major different implementations off IO polling in this
+ * file. The concurrent and non-concurrent implementations.
+ * When available epoll/kqueue are used to implement the concurrent
+ * versions. poll, select and dev/poll use non-concurrent updates.
+ *
+ * Concurrent version:
+ *   In the concurrent version erts_poll_control directly modifies
+ *   the kernel pollset without waking the thread that is waiting
+ *   on events. Also the ErtsPollResFd type is directly mapped to
+ *   the native event type, so no extra copying is needed. Note that
+ *   as no locking at all is done, fds can be triggered that have been
+ *   removed from the pollset. The check_io layer has to deal with this.
+ *
+ * Non-concurrent version:
+ *   In the non-concurrent version, the pollset has an internal representation
+ *   of the pollset that is updated by erts_poll_control. When an fd is updated,
+ *   its number is placed in the update request queue and then the waiting thread
+ *   is woken in order to see the change. The internal data in the pollset is
+ *   protected by a mutex that has to be taken by both the modifying and waiting
+ *   thread at different times.
  *
+ *   The non-concurrent pollset cannot have fd's closed in it while a thread is
+ *   waiting on that fd. In order to fix this, when an ERTS_POLL_OP_DEL command
+ *   is issued, the fd is marked as closing and the waiting thread is woken. The
+ *   fd is then returned in the waiting threads results as ERTS_POLL_EV_NONE.
  *
- * Author: 	Rickard Green
  */
 
 #ifdef HAVE_CONFIG_H
@@ -62,6 +85,8 @@
 #  ifdef SYS_SELECT_H
 #    include <sys/select.h>
 #  endif
+#elif defined(_DARWIN_UNLIMITED_SELECT)
+#  undef _DARWIN_UNLIMITED_SELECT
 #endif
 #ifdef NO_SYSCONF
 #  if ERTS_POLL_USE_SELECT
@@ -83,20 +108,35 @@
 #error "Missing implementation of erts_poll()"
 #endif
 
-#if defined(ERTS_KERNEL_POLL_VERSION) && !ERTS_POLL_USE_KERNEL_POLL
-#error "Missing kernel poll implementation of erts_poll()"
-#endif
+#if 0
+#define ERTS_POLL_DEBUG_PRINT 1
+
+#define DEBUG_PRINT(FMT, PS, ...)                                       \
+    do {                                                                \
+        int myerrno = errno;                                            \
+        erts_printf("%d: " FMT "\r\n", (PS)->id, ##__VA_ARGS__);        \
+        errno = myerrno;                                                \
+    } while(0)
 
-#if defined(ERTS_NO_KERNEL_POLL_VERSION) && ERTS_POLL_USE_KERNEL_POLL
-#error "Kernel poll used when it shouldn't be used"
+/* Define to print info about modifications done to each fd */
+#define DEBUG_PRINT_FD(FMT, PS, FD, ...) DEBUG_PRINT("%d: " FMT, PS, FD, ##__VA_ARGS__)
+/* Define to print entry and exit from erts_poll_wait (can be very spammy) */
+//#define DEBUG_PRINT_WAIT(FMT, PS, ...) DEBUG_PRINT(FMT, PS, ##__VA_ARGS__)
+
+#else
+#define ERTS_POLL_DEBUG_PRINT 0
+#define DEBUG_PRINT(...)
 #endif
 
-#if 0
-#define ERTS_POLL_DEBUG_PRINT
+#ifndef DEBUG_PRINT_FD
+#define DEBUG_PRINT_FD(...)
+#endif
+#ifndef DEBUG_PRINT_WAIT
+#define DEBUG_PRINT_WAIT(...)
 #endif
 
 
-#ifdef _DARWIN_UNLIMITED_SELECT
+#if defined(_DARWIN_UNLIMITED_SELECT) && ERTS_POLL_USE_SELECT
 typedef struct {
     size_t sz;
     fd_set* ptr;
@@ -142,25 +182,13 @@ int ERTS_SELECT(int nfds, ERTS_fd_set *readfds, ERTS_fd_set *writefds,
 #  define ERTS_SELECT	select
 #endif
 
-#define ERTS_POLL_USE_BATCH_UPDATE_POLLSET (ERTS_POLL_USE_DEVPOLL \
-					    || ERTS_POLL_USE_KQUEUE)
+#define ERTS_POLL_IS_FALLBACK (ERTS_POLL_USE_POLL || ERTS_POLL_USE_SELECT) && ERTS_ENABLE_KERNEL_POLL
 
-#define ERTS_POLL_USE_CONCURRENT_UPDATE ERTS_POLL_USE_EPOLL
+#define ERTS_POLL_USE_CONCURRENT_UPDATE (ERTS_POLL_USE_EPOLL || ERTS_POLL_USE_KQUEUE)
 
-#define ERTS_POLL_COALESCE_KP_RES (ERTS_POLL_USE_KQUEUE || ERTS_POLL_USE_EPOLL)
-
-#define ERTS_POLLSET_LOCK(PS) \
-  erts_mtx_lock(&(PS)->mtx)
-#define ERTS_POLLSET_UNLOCK(PS) \
-  erts_mtx_unlock(&(PS)->mtx)
-
-#define ERTS_POLLSET_SET_POLLED_CHK(PS) \
-  ((int) erts_atomic32_xchg_nob(&(PS)->polled, (erts_aint32_t) 1))
-#define ERTS_POLLSET_UNSET_POLLED(PS) \
-  erts_atomic32_set_nob(&(PS)->polled, (erts_aint32_t) 0)
-#define ERTS_POLLSET_IS_POLLED(PS) \
-  ((int) erts_atomic32_read_nob(&(PS)->polled))
+#define ERTS_POLL_USE_WAKEUP_PIPE (!ERTS_POLL_USE_CONCURRENT_UPDATE)
 
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
 
 #define ERTS_POLLSET_SET_HAVE_UPDATE_REQUESTS(PS) \
   erts_atomic32_set_nob(&(PS)->have_update_requests, (erts_aint32_t) 1)
@@ -169,17 +197,28 @@ int ERTS_SELECT(int nfds, ERTS_fd_set *readfds, ERTS_fd_set *writefds,
 #define ERTS_POLLSET_HAVE_UPDATE_REQUESTS(PS) \
   ((int) erts_atomic32_read_nob(&(PS)->have_update_requests))
 
-#if ERTS_POLL_USE_FALLBACK
-#  if ERTS_POLL_USE_POLL
-#    define ERTS_POLL_NEED_FALLBACK(PS) ((PS)->no_poll_fds > 1)
-#  elif ERTS_POLL_USE_SELECT
-#    define ERTS_POLL_NEED_FALLBACK(PS) ((PS)->no_select_fds > 1)
-#  endif
+#define ERTS_POLLSET_LOCK(PS) \
+  erts_mtx_lock(&(PS)->mtx)
+#define ERTS_POLLSET_UNLOCK(PS) \
+  erts_mtx_unlock(&(PS)->mtx)
+
+#else
+
+#define ERTS_POLLSET_SET_HAVE_UPDATE_REQUESTS(PS)
+#define ERTS_POLLSET_UNSET_HAVE_UPDATE_REQUESTS(PS)
+#define ERTS_POLLSET_HAVE_UPDATE_REQUESTS(PS) 0
+
+#define ERTS_POLLSET_LOCK(PS)
+#define ERTS_POLLSET_UNLOCK(PS)
+
 #endif
+
 /*
  * --- Data types ------------------------------------------------------------
  */
 
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
+
 #define ERTS_POLLSET_UPDATE_REQ_BLOCK_SIZE 128
 
 typedef struct ErtsPollSetUpdateRequestsBlock_ ErtsPollSetUpdateRequestsBlock;
@@ -189,237 +228,200 @@ struct ErtsPollSetUpdateRequestsBlock_ {
     int fds[ERTS_POLLSET_UPDATE_REQ_BLOCK_SIZE];
 };
 
-
-
 #  define ERTS_POLL_FD_FLG_INURQ	(((unsigned short) 1) << 0)
-#if ERTS_POLL_USE_FALLBACK
-#  define ERTS_POLL_FD_FLG_INFLBCK	(((unsigned short) 1) << 1)
-#  define ERTS_POLL_FD_FLG_USEFLBCK	(((unsigned short) 1) << 2)
-#endif
-#  define ERTS_POLL_FD_FLG_RST		(((unsigned short) 1) << 3)
+#  define ERTS_POLL_FD_FLG_RST		(((unsigned short) 1) << 1)
+
 typedef struct {
 #if ERTS_POLL_USE_POLL
     int pix;
 #endif
+
     ErtsPollEvents used_events;
     ErtsPollEvents events;
-#if ERTS_POLL_COALESCE_KP_RES
-    unsigned short res_ev_ix;
-#endif
     unsigned short flags;
 
 } ErtsFdStatus;
 
-
-#if ERTS_POLL_COALESCE_KP_RES
-/* res_ev_ix max value */
-#define ERTS_POLL_MAX_RES ((1 << sizeof(unsigned short)*8) - 1)
 #endif
 
-#if ERTS_POLL_USE_KQUEUE
-
-#define ERTS_POLL_KQ_OP_HANDLED			1
-#define ERTS_POLL_KQ_OP_DEL_R			2
-#define ERTS_POLL_KQ_OP_DEL_W			3
-#define ERTS_POLL_KQ_OP_ADD_R			4
-#define ERTS_POLL_KQ_OP_ADD_W			5
-#define ERTS_POLL_KQ_OP_ADD2_R			6
-#define ERTS_POLL_KQ_OP_ADD2_W			7
-
-#endif
-
-struct ErtsPollSet_ {
-    ErtsPollSet next;
+/*
+ * This struct is not really exported, but it's nice to
+ * get unique names in debugger for kp/nkp
+ */
+struct ERTS_POLL_EXPORT(erts_pollset) {
+    int id;
     int internal_fd_limit;
-    ErtsFdStatus *fds_status;
     erts_atomic_t no_of_user_fds;
-    int fds_status_len;
+
 #if ERTS_POLL_USE_KERNEL_POLL
     int kp_fd;
-    int res_events_len;
-#if ERTS_POLL_USE_EPOLL
-    struct epoll_event *res_events;
-#elif ERTS_POLL_USE_KQUEUE
-    struct kevent *res_events;
-#elif ERTS_POLL_USE_DEVPOLL
-    struct pollfd *res_events;
-#endif
 #endif /* ERTS_POLL_USE_KERNEL_POLL */
+
 #if ERTS_POLL_USE_POLL
     int next_poll_fds_ix;
     int no_poll_fds;
     int poll_fds_len;
-    struct pollfd*poll_fds;
+    struct pollfd *poll_fds;
 #elif ERTS_POLL_USE_SELECT
     int next_sel_fd;
     int max_fd;
-#if ERTS_POLL_USE_FALLBACK
-    int no_select_fds;
-#endif
     ERTS_fd_set input_fds;
     ERTS_fd_set res_input_fds;
     ERTS_fd_set output_fds;
     ERTS_fd_set res_output_fds;
+#elif ERTS_POLL_USE_DEVPOLL
+    struct pollfd *poll_fds;
+    int poll_fds_ix;
 #endif
+
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
+    ErtsFdStatus *fds_status;
+    int fds_status_len;
     ErtsPollSetUpdateRequestsBlock update_requests;
     ErtsPollSetUpdateRequestsBlock *curr_upd_req_block;
     erts_atomic32_t have_update_requests;
-    erts_atomic32_t polled;
     erts_mtx_t mtx;
-    int wake_fds[2];
-#if ERTS_POLL_USE_TIMERFD
-    int timer_fd;
-#endif
-#if ERTS_POLL_USE_FALLBACK
-    int fallback_used;
-#endif
     erts_atomic32_t wakeup_state;
-    erts_atomic64_t timeout_time;
-#ifdef ERTS_POLL_COUNT_AVOIDED_WAKEUPS
-    erts_atomic_t no_avoided_wakeups;
-    erts_atomic_t no_avoided_interrupts;
-    erts_atomic_t no_interrupt_timed;
+#endif
+
+#if ERTS_POLL_USE_WAKEUP_PIPE
+    int wake_fds[2];
 #endif
 };
 
 void erts_silence_warn_unused_result(long unused);
 static void fatal_error(char *format, ...);
-static void fatal_error_async_signal_safe(char *error_str);
 
 static int max_fds = -1;
-static ErtsPollSet pollsets;
-static erts_mtx_t pollsets_lock;
 
 #if ERTS_POLL_USE_POLL
 
+#if !ERTS_POLL_IS_FALLBACK
+static ERTS_INLINE short ev2pollev(ErtsPollEvents ev)
+{
+    return ERTS_POLL_EV_E2N(ev);
+}
+
+static ERTS_INLINE ErtsPollEvents pollev2ev(short ev)
+{
+    return ERTS_POLL_EV_N2E(ev);
+}
+
+#else /* ERTS_POLL_IS_FALLBACK */
+
 static ERTS_INLINE short
 ev2pollev(ErtsPollEvents ev)
 {
-#if !ERTS_POLL_USE_FALLBACK || ERTS_POLL_USE_KQUEUE
-    return ERTS_POLL_EV_E2N(ev);
-#else /* Note, we only map events we are interested in */
     short res_ev = (short) 0;
     if (ev & ERTS_POLL_EV_IN)
-	res_ev |= ERTS_POLL_EV_NKP_IN;
+       res_ev |= ERTS_POLL_EV_NKP_IN;
     if (ev & ERTS_POLL_EV_OUT)
-	res_ev |= ERTS_POLL_EV_NKP_OUT;
+       res_ev |= ERTS_POLL_EV_NKP_OUT;
     return res_ev;
-#endif
 }
 
 static ERTS_INLINE ErtsPollEvents
 pollev2ev(short ev)
 {
-#if !ERTS_POLL_USE_FALLBACK || ERTS_POLL_USE_KQUEUE
-    return ERTS_POLL_EV_N2E(ev);
-#else /* Note, we only map events we are interested in */
     ErtsPollEvents res_ev = (ErtsPollEvents) 0;
     if (ev & ERTS_POLL_EV_NKP_IN)
-	res_ev |= ERTS_POLL_EV_IN;
+       res_ev |= ERTS_POLL_EV_IN;
     if (ev & ERTS_POLL_EV_NKP_OUT)
-	res_ev |= ERTS_POLL_EV_OUT;
+       res_ev |= ERTS_POLL_EV_OUT;
     if (ev & ERTS_POLL_EV_NKP_ERR)
-	res_ev |= ERTS_POLL_EV_ERR;
+       res_ev |= ERTS_POLL_EV_ERR;
     if (ev & ERTS_POLL_EV_NKP_NVAL)
-	res_ev |= ERTS_POLL_EV_NVAL;
-    return res_ev;
-#endif
+       res_ev |= ERTS_POLL_EV_NVAL;
+   return res_ev;
 }
 
-#endif
+#endif /* !ERTS_POLL_IS_FALLBACK */
+
+#endif /* ERTS_POLL_USE_POLL */
+
 
 #ifdef HARD_DEBUG
 static void check_poll_result(ErtsPollResFd pr[], int len);
-#if ERTS_POLL_USE_DEVPOLL
-static void check_poll_status(ErtsPollSet ps);
-#endif /* ERTS_POLL_USE_DEVPOLL */
 #endif /* HARD_DEBUG */
-#ifdef ERTS_POLL_DEBUG_PRINT
+#if ERTS_POLL_USE_DEVPOLL && defined(DEBUG)
+static void check_poll_status(ErtsPollSet *ps);
+#endif /* ERTS_POLL_USE_DEVPOLL && DEBUG */
 static void print_misc_debug_info(void);
+#if ERTS_POLL_USE_EPOLL
+uint32_t epoll_events(int kp_fd, int fd);
 #endif
 
-static ERTS_INLINE void
-init_timeout_time(ErtsPollSet ps)
-{
-    erts_atomic64_init_nob(&ps->timeout_time,
-			   (erts_aint64_t) ERTS_MONOTONIC_TIME_MAX);
-}
-
-static ERTS_INLINE void
-set_timeout_time(ErtsPollSet ps, ErtsMonotonicTime time)
-{
-    erts_atomic64_set_relb(&ps->timeout_time,
-			   (erts_aint64_t) time);
-}
-
-static ERTS_INLINE ErtsMonotonicTime
-get_timeout_time(ErtsPollSet ps)
-{
-    return (ErtsMonotonicTime) erts_atomic64_read_acqb(&ps->timeout_time);
-}
 
 #define ERTS_POLL_NOT_WOKEN	0
 #define ERTS_POLL_WOKEN		-1
 #define ERTS_POLL_WOKEN_INTR	1
 
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
 static ERTS_INLINE void
-reset_wakeup_state(ErtsPollSet ps)
+reset_wakeup_state(ErtsPollSet *ps)
 {
     erts_atomic32_set_mb(&ps->wakeup_state, ERTS_POLL_NOT_WOKEN);
 }
+#endif
 
 static ERTS_INLINE int
-is_woken(ErtsPollSet ps)
+is_woken(ErtsPollSet *ps)
 {
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
     return erts_atomic32_read_acqb(&ps->wakeup_state) != ERTS_POLL_NOT_WOKEN;
+#else
+    return 0;
+#endif
 }
 
 static ERTS_INLINE int
-is_interrupted_reset(ErtsPollSet ps)
+is_interrupted_reset(ErtsPollSet *ps)
 {
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
     return (erts_atomic32_xchg_acqb(&ps->wakeup_state, ERTS_POLL_NOT_WOKEN)
 	    == ERTS_POLL_WOKEN_INTR);
+#else
+    return 0;
+#endif
 }
 
 static ERTS_INLINE void
-woke_up(ErtsPollSet ps)
+woke_up(ErtsPollSet *ps)
 {
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
     erts_aint32_t wakeup_state = erts_atomic32_read_acqb(&ps->wakeup_state);
     if (wakeup_state == ERTS_POLL_NOT_WOKEN)
 	(void) erts_atomic32_cmpxchg_nob(&ps->wakeup_state,
 					 ERTS_POLL_WOKEN,
 					 ERTS_POLL_NOT_WOKEN);
     ASSERT(erts_atomic32_read_nob(&ps->wakeup_state) != ERTS_POLL_NOT_WOKEN);
+#endif
 }
 
 /*
  * --- Wakeup pipe -----------------------------------------------------------
  */
 
+#if ERTS_POLL_USE_WAKEUP_PIPE
 
 static ERTS_INLINE void
-wake_poller(ErtsPollSet ps, int interrupted, int async_signal_safe)
+wake_poller(ErtsPollSet *ps, int interrupted)
 {
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
     int wake;
-    if (async_signal_safe)
-	wake = 1;
-    else {
-	erts_aint32_t wakeup_state;
-	if (!interrupted)
-	    wakeup_state = erts_atomic32_cmpxchg_relb(&ps->wakeup_state,
-						      ERTS_POLL_WOKEN,
-						      ERTS_POLL_NOT_WOKEN);
-	else
-            wakeup_state = erts_atomic32_xchg_relb(&ps->wakeup_state,
-                                                   ERTS_POLL_WOKEN_INTR);
-	wake = wakeup_state == ERTS_POLL_NOT_WOKEN;
-    }
-    /*
-     * NOTE: This function might be called from signal handlers in the
-     *       non-smp case; therefore, it has to be async-signal safe in
-     *       the non-smp case.
-     */
-    if (wake) {
+    erts_aint32_t wakeup_state;
+    if (!interrupted)
+        wakeup_state = erts_atomic32_cmpxchg_relb(&ps->wakeup_state,
+                                                  ERTS_POLL_WOKEN,
+                                                  ERTS_POLL_NOT_WOKEN);
+    else
+        wakeup_state = erts_atomic32_xchg_relb(&ps->wakeup_state,
+                                               ERTS_POLL_WOKEN_INTR);
+    wake = wakeup_state == ERTS_POLL_NOT_WOKEN;
+
+    if (wake)
+#endif
+    {
 	ssize_t res;
 	if (ps->wake_fds[1] < 0)
 	    return; /* Not initialized yet */
@@ -428,29 +430,27 @@ wake_poller(ErtsPollSet ps, int interrupted, int async_signal_safe)
 	    res = write(ps->wake_fds[1], "!", 1);
 	} while (res < 0 && errno == EINTR);
 	if (res <= 0 && errno != ERRNO_BLOCK) {
-	    if (async_signal_safe)
-		fatal_error_async_signal_safe(__FILE__
-					      ":XXX:wake_poller(): "
-					      "Failed to write on wakeup pipe\n");
-	    else
-		fatal_error("%s:%d:wake_poller(): "
-			    "Failed to write to wakeup pipe fd=%d: "
-			    "%s (%d)\n",
-			    __FILE__, __LINE__,
-			    ps->wake_fds[1],
-			    erl_errno_id(errno), errno);
+            fatal_error("%s:%d:wake_poller(): "
+                        "Failed to write to wakeup pipe fd=%d: "
+                        "%s (%d)\n",
+                        __FILE__, __LINE__,
+                        ps->wake_fds[1],
+                        erl_errno_id(errno), errno);
 	}
     }
 }
 
 static ERTS_INLINE void
-cleanup_wakeup_pipe(ErtsPollSet ps)
+cleanup_wakeup_pipe(ErtsPollSet *ps)
 {
+    int intr = 0;
     int fd = ps->wake_fds[0];
     int res;
     do {
 	char buf[32];
 	res = read(fd, buf, sizeof(buf));
+	if (res > 0)
+	    intr = 1;
     } while (res > 0 || (res < 0 && errno == EINTR));
     if (res < 0 && errno != ERRNO_BLOCK) {
 	fatal_error("%s:%d:cleanup_wakeup_pipe(): "
@@ -460,10 +460,14 @@ cleanup_wakeup_pipe(ErtsPollSet ps)
 		    fd,
 		    erl_errno_id(errno), errno);
     }
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
+    if (intr)
+	erts_atomic32_set_nob(&ps->wakeup_state, ERTS_POLL_WOKEN_INTR);
+#endif
 }
 
 static void
-create_wakeup_pipe(ErtsPollSet ps)
+create_wakeup_pipe(ErtsPollSet *ps)
 {
     int do_wake = 0;
     int wake_fds[2];
@@ -480,20 +484,13 @@ create_wakeup_pipe(ErtsPollSet ps)
     SET_NONBLOCKING(wake_fds[0]);
     SET_NONBLOCKING(wake_fds[1]);
 
-#ifdef ERTS_POLL_DEBUG_PRINT
-    erts_printf("wakeup fds = {%d, %d}\n", wake_fds[0], wake_fds[1]);
-#endif
+    DEBUG_PRINT("wakeup fds = {%d, %d}", ps, wake_fds[0], wake_fds[1]);
 
     ERTS_POLL_EXPORT(erts_poll_control)(ps,
 					wake_fds[0],
+                                        ERTS_POLL_OP_ADD,
 					ERTS_POLL_EV_IN,
-					1, &do_wake);
-#if ERTS_POLL_USE_FALLBACK
-    /* We depend on the wakeup pipe being handled by kernel poll */
-    if (ps->fds_status[wake_fds[0]].flags & ERTS_POLL_FD_FLG_INFLBCK)
-	fatal_error("%s:%d:create_wakeup_pipe(): Internal error\n",
-		    __FILE__, __LINE__);
-#endif
+                                        &do_wake);
     if (ps->internal_fd_limit <= wake_fds[1])
 	ps->internal_fd_limit = wake_fds[1] + 1;
     if (ps->internal_fd_limit <= wake_fds[0])
@@ -502,82 +499,16 @@ create_wakeup_pipe(ErtsPollSet ps)
     ps->wake_fds[1] = wake_fds[1];
 }
 
-
-/*
- * --- timer fd -----------------------------------------------------------
- */
-
-#if ERTS_POLL_USE_TIMERFD
-
-/* We use the timerfd when using epoll_wait to get high accuracy
-   timeouts, i.e. we want to sleep with < ms accuracy. */
-
-static void
-create_timerfd(ErtsPollSet ps)
-{
-    int do_wake = 0;
-    int timer_fd;
-    timer_fd = timerfd_create(CLOCK_MONOTONIC,0);
-    ERTS_POLL_EXPORT(erts_poll_control)(ps,
-					timer_fd,
-					ERTS_POLL_EV_IN,
-					1, &do_wake);
-#if ERTS_POLL_USE_FALLBACK
-    /* We depend on the wakeup pipe being handled by kernel poll */
-    if (ps->fds_status[timer_fd].flags & ERTS_POLL_FD_FLG_INFLBCK)
-	fatal_error("%s:%d:create_wakeup_pipe(): Internal error\n",
-		    __FILE__, __LINE__);
 #endif
-    if (ps->internal_fd_limit <= timer_fd)
-	ps->internal_fd_limit = timer_fd + 1;
-    ps->timer_fd = timer_fd;
-}
-
-static ERTS_INLINE void
-timerfd_set(ErtsPollSet ps, struct itimerspec *its)
-{
-#ifdef DEBUG
-    struct itimerspec old_its;
-    int res;
-    res = timerfd_settime(ps->timer_fd, 0, its, &old_its);
-    ASSERT(res == 0);
-    ASSERT(old_its.it_interval.tv_sec == 0 &&
-           old_its.it_interval.tv_nsec == 0 &&
-           old_its.it_value.tv_sec == 0 &&
-           old_its.it_value.tv_nsec == 0);
-
-#else
-    timerfd_settime(ps->timer_fd, 0, its, NULL);
-#endif
-}
-
-static ERTS_INLINE int
-timerfd_clear(ErtsPollSet ps, int res, int max_res) {
-
-    struct itimerspec its;
-    /* we always have to clear the timer */
-    its.it_interval.tv_sec = 0;
-    its.it_interval.tv_nsec = 0;
-    its.it_value.tv_sec = 0;
-    its.it_value.tv_nsec = 0;
-    timerfd_settime(ps->timer_fd, 0, &its, NULL);
-
-    /* only timeout fd triggered */
-    if (res == 1 && ps->res_events[0].data.fd == ps->timer_fd)
-        return 0;
-
-    return res;
-}
-
-#endif /* ERTS_POLL_USE_TIMERFD */
-
 
 /*
  * --- Poll set update requests ----------------------------------------------
  */
 
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
+
 static ERTS_INLINE void
-enqueue_update_request(ErtsPollSet ps, int fd)
+enqueue_update_request(ErtsPollSet *ps, int fd)
 {
     ErtsPollSetUpdateRequestsBlock *urqbp;
 
@@ -592,13 +523,11 @@ enqueue_update_request(ErtsPollSet ps, int fd)
     urqbp = ps->curr_upd_req_block;
 
     if (urqbp->len == ERTS_POLLSET_UPDATE_REQ_BLOCK_SIZE) {
-	ASSERT(!urqbp->next);
 	urqbp = erts_alloc(ERTS_ALC_T_POLLSET_UPDREQ,
 			   sizeof(ErtsPollSetUpdateRequestsBlock));
-	ps->curr_upd_req_block->next = urqbp;
-	ps->curr_upd_req_block = urqbp;
-	urqbp->next = NULL;
+	urqbp->next = ps->curr_upd_req_block;
 	urqbp->len = 0;
+	ps->curr_upd_req_block = urqbp;
     }
 
     ps->fds_status[fd].flags |= ERTS_POLL_FD_FLG_INURQ;
@@ -606,28 +535,29 @@ enqueue_update_request(ErtsPollSet ps, int fd)
 }
 
 static ERTS_INLINE void
-free_update_requests_block(ErtsPollSet ps,
+free_update_requests_block(ErtsPollSet *ps,
 			   ErtsPollSetUpdateRequestsBlock *urqbp)
 {
     if (urqbp != &ps->update_requests)
 	erts_free(ERTS_ALC_T_POLLSET_UPDREQ, (void *) urqbp);
     else {
-	urqbp->next = NULL;
 	urqbp->len = 0;
     }
 }
 
+#endif /* !ERTS_POLL_USE_CONCURRENT_UPDATE */
 
 /*
  * --- Growing poll set structures -------------------------------------------
  */
 
-#ifndef ERTS_KERNEL_POLL_VERSION   /* only one shared implementation */
+#if !ERTS_NO_KERNEL_POLL_VERSION || !ERTS_ENABLE_KERNEL_POLL
+/* only one shared implementation */
 
 #define ERTS_FD_TABLE_MIN_LENGTH	1024
 #define ERTS_FD_TABLE_EXP_THRESHOLD	(2048*1024)
 
-int erts_poll_new_table_len (int old_len, int need_len)
+int erts_poll_new_table_len(int old_len, int need_len)
 {
     int new_len;
 
@@ -637,7 +567,7 @@ int erts_poll_new_table_len (int old_len, int need_len)
     }
     else {
         new_len = old_len;
-        do {            
+        do {
             if (new_len < ERTS_FD_TABLE_EXP_THRESHOLD)
                 new_len *= 2;
             else
@@ -650,30 +580,9 @@ int erts_poll_new_table_len (int old_len, int need_len)
 }
 #endif
 
-#if ERTS_POLL_USE_KERNEL_POLL
-static void
-grow_res_events(ErtsPollSet ps, int new_len)
-{
-    size_t new_size = sizeof(
-#if ERTS_POLL_USE_EPOLL
-	struct epoll_event
-#elif ERTS_POLL_USE_DEVPOLL
-	struct pollfd
-#elif ERTS_POLL_USE_KQUEUE
-	struct kevent
-#endif
-	) * erts_poll_new_table_len(ps->res_events_len, new_len);
-    /* We do not need to save previously stored data */
-    if (ps->res_events)
-	erts_free(ERTS_ALC_T_POLL_RES_EVS, ps->res_events);
-    ps->res_events = erts_alloc(ERTS_ALC_T_POLL_RES_EVS, new_size);
-    ps->res_events_len = new_len;
-}
-#endif /* ERTS_POLL_USE_KERNEL_POLL */
-
 #if ERTS_POLL_USE_POLL
 static void
-grow_poll_fds(ErtsPollSet ps, int min_ix)
+grow_poll_fds(ErtsPollSet *ps, int min_ix)
 {
     int i;
     int new_len = erts_poll_new_table_len(ps->poll_fds_len, min_ix + 1);
@@ -721,8 +630,9 @@ ensure_select_fds(int fd, ERTS_fd_set* in, ERTS_fd_set* out)
 #  define ensure_select_fds(fd, in, out) do {} while(0)
 #endif /* _DARWIN_UNLIMITED_SELECT */
 
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
 static void
-grow_fds_status(ErtsPollSet ps, int min_fd)
+grow_fds_status(ErtsPollSet *ps, int min_fd)
 {
     int i;
     int new_len = erts_poll_new_table_len(ps->fds_status_len, min_fd + 1);
@@ -741,428 +651,26 @@ grow_fds_status(ErtsPollSet ps, int min_fd)
 #endif
 	ps->fds_status[i].used_events = (ErtsPollEvents) 0;
 	ps->fds_status[i].events = (ErtsPollEvents) 0;
-#if ERTS_POLL_COALESCE_KP_RES
-	ps->fds_status[i].res_ev_ix = (unsigned short) ERTS_POLL_MAX_RES;
-#endif
 	ps->fds_status[i].flags = (unsigned short) 0;
     }
     ps->fds_status_len = new_len;
 }
+#endif
 
 /*
  * --- Selecting fd to poll on -----------------------------------------------
  */
 
-#if ERTS_POLL_USE_FALLBACK
-static int update_fallback_pollset(ErtsPollSet ps, int fd);
-#endif
-
-static ERTS_INLINE int
-need_update(ErtsPollSet ps, int fd)
-{
-#if ERTS_POLL_USE_KERNEL_POLL
-    int reset;
-#endif
-
-    ASSERT(fd < ps->fds_status_len);
-
-#if ERTS_POLL_USE_KERNEL_POLL
-    reset = (int) (ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_RST);
-    if (reset && !ps->fds_status[fd].used_events) {
-	ps->fds_status[fd].flags &= ~ERTS_POLL_FD_FLG_RST;
-	reset = 0;
-    }
-#else
-    ps->fds_status[fd].flags &= ~ERTS_POLL_FD_FLG_RST;
-#endif
-
-    if (ps->fds_status[fd].used_events != ps->fds_status[fd].events)
-	return 1;
-
-#if ERTS_POLL_USE_KERNEL_POLL
-    return reset;
-#else
-    return 0;
-#endif
-}
-
-#if ERTS_POLL_USE_BATCH_UPDATE_POLLSET
-
-#if ERTS_POLL_USE_KQUEUE
-#define ERTS_POLL_MIN_BATCH_BUF_SIZE 128
-#else
-#define ERTS_POLL_MIN_BATCH_BUF_SIZE 64
-#endif
-
-typedef struct {
-    int len;
-    int size;
-#if ERTS_POLL_USE_DEVPOLL
-    struct pollfd *buf;
-#elif ERTS_POLL_USE_KQUEUE
-    struct kevent *buf;
-    struct kevent *ebuf;
-#endif
-} ErtsPollBatchBuf;
-
-
-static ERTS_INLINE void
-setup_batch_buf(ErtsPollSet ps, ErtsPollBatchBuf *bbp)
-{
-    bbp->len = 0;
-#if ERTS_POLL_USE_DEVPOLL
-    bbp->size = ps->res_events_len;
-    bbp->buf = ps->res_events;
-#elif ERTS_POLL_USE_KQUEUE
-    bbp->size = ps->res_events_len/2;
-    bbp->buf = ps->res_events;
-    bbp->ebuf = bbp->buf + bbp->size;
-#endif
-}
-
-
-#if ERTS_POLL_USE_DEVPOLL
-
-static void
-write_batch_buf(ErtsPollSet ps, ErtsPollBatchBuf *bbp)
-{
-    ssize_t wres;
-    char *buf = (char *) bbp->buf;
-    size_t buf_size = sizeof(struct pollfd)*bbp->len;
-    
-    while (1) {
-	wres = write(ps->kp_fd, (void *) buf, buf_size);
-	if (wres < 0) {
-	    if (errno == EINTR)
-		continue;
-	    fatal_error("%s:%d:write_batch_buf(): "
-			"Failed to write to /dev/poll: "
-			"%s (%d)\n",
-			__FILE__, __LINE__,
-			erl_errno_id(errno), errno);
-	}
-	buf_size -= wres;
-	if (buf_size <= 0)
-	    break;
-	buf += wres;
-    }
-
-    if (buf_size < 0) {
-	fatal_error("%s:%d:write_devpoll_buf(): Internal error\n",
-		    __FILE__, __LINE__);
-    }
-    bbp->len = 0;
-}
-
-#elif ERTS_POLL_USE_KQUEUE
-
-static void
-write_batch_buf(ErtsPollSet ps, ErtsPollBatchBuf *bbp)
-{
-    int res;
-    int len = bbp->len;
-    struct kevent *buf = bbp->buf;
-    struct timespec ts = {0, 0};
-
-    do {
-	res = kevent(ps->kp_fd, buf, len, NULL, 0, &ts);
-    } while (res < 0 && errno == EINTR);
-    if (res < 0) {
-	int i;
-	struct kevent *ebuf = bbp->ebuf;
-	do {
-	    res = kevent(ps->kp_fd, buf, len, ebuf, len, &ts);
-	} while (res < 0 && errno == EINTR);
-	if (res < 0) {
-	    fatal_error("%s:%d: kevent() failed: %s (%d)\n",
-			__FILE__, __LINE__, erl_errno_id(errno), errno);
-	}
-	for (i = 0; i < res; i++) {
-	    if (ebuf[i].flags & EV_ERROR) {
-		short filter;
-		int fd = (int) ebuf[i].ident;
-
-		switch ((int) (long) ebuf[i].udata) {
-
-		    /*
-		     * Since we use a lazy update approach EV_DELETE will
-		     * frequently fail. This since kqueue automatically
-		     * removes a file descriptor that is closed from the
-		     * poll set.
-		     */
-		case ERTS_POLL_KQ_OP_DEL_R:
-		case ERTS_POLL_KQ_OP_DEL_W:
-		case ERTS_POLL_KQ_OP_HANDLED:
-		    break;
-
-		    /*
-		     * According to the kqueue man page EVFILT_READ support
-		     * does not imply EVFILT_WRITE support; therefore,
-		     * if an EV_ADD fail, we may have to remove other
-		     * events on this fd in the kqueue pollset before
-		     * adding fd to the fallback pollset.
-		     */
-		case ERTS_POLL_KQ_OP_ADD_W:
-		    if (ps->fds_status[fd].used_events & ERTS_POLL_EV_IN) {
-			filter = EVFILT_READ;
-			goto rm_add_fb;
-		    }
-		    goto add_fb;
-		case ERTS_POLL_KQ_OP_ADD_R:
-		    if (ps->fds_status[fd].used_events & ERTS_POLL_EV_OUT) {
-			filter = EVFILT_WRITE;
-			goto rm_add_fb;
-		    }
-		    goto add_fb;
-		case ERTS_POLL_KQ_OP_ADD2_W:
-		case ERTS_POLL_KQ_OP_ADD2_R: {
-		    int j;
-		    for (j = i+1; j < res; j++) {
-			if (fd == (int) ebuf[j].ident) {
-			    ebuf[j].udata = (void *) ERTS_POLL_KQ_OP_HANDLED;
-			    if (!(ebuf[j].flags & EV_ERROR)) {
-				switch ((int) (long) ebuf[j].udata) {
-				case ERTS_POLL_KQ_OP_ADD2_W:
-				    filter = EVFILT_WRITE;
-				    goto rm_add_fb;
-				case ERTS_POLL_KQ_OP_ADD2_R:
-				    filter = EVFILT_READ;
-				    goto rm_add_fb;
-				default:
-				    fatal_error("%s:%d:write_batch_buf(): "
-						"Internal error",
-						__FILE__, __LINE__);
-				    break;
-				}
-			    }
-			    goto add_fb;
-			}
-		    }
-		    /* The other add succeded... */
-		    filter = ((((int) (long) ebuf[i].udata)
-			       == ERTS_POLL_KQ_OP_ADD2_W)
-			      ? EVFILT_READ
-			      : EVFILT_WRITE);
-		rm_add_fb:
-		    { 
-			struct kevent kev;
-			struct timespec ts = {0, 0};
-			EV_SET(&kev, fd, filter, EV_DELETE, 0, 0, 0);
-			(void) kevent(ps->kp_fd, &kev, 1, NULL, 0, &ts);
-		    }
-
-		add_fb:
-		    ps->fds_status[fd].flags |= ERTS_POLL_FD_FLG_USEFLBCK;
-		    ASSERT(ps->fds_status[fd].used_events);
-		    ps->fds_status[fd].used_events = 0;
-		    erts_atomic_dec_nob(&ps->no_of_user_fds);
-		    update_fallback_pollset(ps, fd);
-		    ASSERT(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK);
-		    break;
-		}
-		default:
-		    fatal_error("%s:%d:write_batch_buf(): Internal error",
-				__FILE__, __LINE__);
-		    break;
-		}
-	    }
-	}
-    }
-    bbp->len = 0;
-}
-
-#endif /* ERTS_POLL_USE_KQUEUE */
-
-static ERTS_INLINE void
-batch_update_pollset(ErtsPollSet ps, int fd, ErtsPollBatchBuf *bbp)
-{
-    int buf_len;
-#if ERTS_POLL_USE_DEVPOLL
-    short events;
-    struct pollfd *buf;
-#elif ERTS_POLL_USE_KQUEUE
-    struct kevent *buf;
-#endif
-
-#ifdef ERTS_POLL_DEBUG_PRINT
-    erts_printf("Doing lazy update on fd=%d\n", fd);
-#endif
-
-    if (!need_update(ps, fd))
-	return;
-
-    /* Make sure we have room for at least maximum no of entries
-       per fd */
-    if (bbp->size - bbp->len < 2)
-	write_batch_buf(ps, bbp);
-
-    buf_len = bbp->len;
-    buf = bbp->buf;
-
-    ASSERT(fd < ps->fds_status_len);
-
-#if ERTS_POLL_USE_DEVPOLL
-    events = ERTS_POLL_EV_E2N(ps->fds_status[fd].events);
-    if (!events) {
-	buf[buf_len].events = POLLREMOVE;
-	erts_atomic_dec_nob(&ps->no_of_user_fds);
-    }
-    else if (!ps->fds_status[fd].used_events) {
-	buf[buf_len].events = events;
-	erts_atomic_inc_nob(&ps->no_of_user_fds);
-    }
-    else {
-	if ((ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_RST)
-	    || (ps->fds_status[fd].used_events & ~events)) {
-	    /* Reset or removed events... */
-	    buf[buf_len].fd = fd;
-	    buf[buf_len].events = POLLREMOVE;
-	    buf[buf_len++].revents = 0;
-	}
-	buf[buf_len].events = events;
-    }
-    buf[buf_len].fd = fd;
-    buf[buf_len++].revents = 0;
-
-#elif ERTS_POLL_USE_KQUEUE
-
-    if (ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK) {
-	if (ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_USEFLBCK)
-	    update_fallback_pollset(ps, fd);
-	else { /* Remove from fallback and try kqueue */
-	    ErtsPollEvents events = ps->fds_status[fd].events;
-	    ps->fds_status[fd].events = (ErtsPollEvents) 0;
-	    update_fallback_pollset(ps, fd);
-	    ASSERT(!(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK));
-	    if (events) {
-		ps->fds_status[fd].events = events;
-		goto try_kqueue;
-	    }
-	}
-    }
-    else {
-	ErtsPollEvents events, used_events;
-	int mod_w, mod_r;
-    try_kqueue:
-	events = ERTS_POLL_EV_E2N(ps->fds_status[fd].events);
-	used_events = ERTS_POLL_EV_E2N(ps->fds_status[fd].used_events);
-	if (!(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_RST)) {
-	    if (!used_events &&
-		(events & ERTS_POLL_EV_IN) && (events & ERTS_POLL_EV_OUT))
-		goto do_add_rw;
-	    mod_r = ((events & ERTS_POLL_EV_IN)
-		     != (used_events & ERTS_POLL_EV_IN));
-	    mod_w = ((events & ERTS_POLL_EV_OUT)
-		     != (used_events & ERTS_POLL_EV_OUT));
-	    goto do_mod;
-	}
-	else { /* Reset */
-	    if ((events & ERTS_POLL_EV_IN) && (events & ERTS_POLL_EV_OUT)) {
-	    do_add_rw:
-		EV_SET(&buf[buf_len], fd, EVFILT_READ, EV_ADD,
-		       0, 0, (void *) ERTS_POLL_KQ_OP_ADD2_R);
-		buf_len++;
-		EV_SET(&buf[buf_len], fd, EVFILT_WRITE, EV_ADD,
-		       0, 0, (void *) ERTS_POLL_KQ_OP_ADD2_W);
-		buf_len++;
-
-	    }
-	    else {
-		mod_r = 1;
-		mod_w = 1;
-	    do_mod:
-		if (mod_r) {
-		    if (events & ERTS_POLL_EV_IN) {
-			EV_SET(&buf[buf_len], fd, EVFILT_READ, EV_ADD,
-			       0, 0, (void *) ERTS_POLL_KQ_OP_ADD_R);
-			buf_len++;
-		    }
-		    else if (used_events & ERTS_POLL_EV_IN) {
-			EV_SET(&buf[buf_len], fd, EVFILT_READ, EV_DELETE,
-			       0, 0, (void *) ERTS_POLL_KQ_OP_DEL_R);
-			buf_len++;
-		    }
-		}
-		if (mod_w) {
-		    if (events & ERTS_POLL_EV_OUT) {
-			EV_SET(&buf[buf_len], fd, EVFILT_WRITE, EV_ADD,
-			       0, 0, (void *) ERTS_POLL_KQ_OP_ADD_W);
-			buf_len++;
-		    }
-		    else if (used_events & ERTS_POLL_EV_OUT) {
-			EV_SET(&buf[buf_len], fd, EVFILT_WRITE, EV_DELETE,
-			       0, 0, (void *) ERTS_POLL_KQ_OP_DEL_W);
-			buf_len++;
-		    }
-		}
-	    }
-	}
-	if (used_events) {
-	    if (!events) {
-		erts_atomic_dec_nob(&ps->no_of_user_fds);
-	    }
-	}
-	else {
-	    if (events)
-		erts_atomic_inc_nob(&ps->no_of_user_fds);
-	}
-	ASSERT((events & ~(ERTS_POLL_EV_IN|ERTS_POLL_EV_OUT)) == 0);
-	ASSERT((used_events & ~(ERTS_POLL_EV_IN|ERTS_POLL_EV_OUT)) == 0);
-    }	    
-
-#endif
-
-    ps->fds_status[fd].flags &= ~ERTS_POLL_FD_FLG_RST;
-    ps->fds_status[fd].used_events = ps->fds_status[fd].events;
-
-    bbp->len = buf_len;
-}
-
-#else /* !ERTS_POLL_USE_BATCH_UPDATE_POLLSET */
-
 #if ERTS_POLL_USE_EPOLL
 static int
-#if ERTS_POLL_USE_CONCURRENT_UPDATE
-conc_update_pollset(ErtsPollSet ps, int fd, int *update_fallback)
-#else
-update_pollset(ErtsPollSet ps, int fd)
-#endif
+update_pollset(ErtsPollSet *ps, int fd, ErtsPollOp op, ErtsPollEvents events)
 {
     int res;
-    int op;
+    int epoll_op = EPOLL_CTL_MOD;
     struct epoll_event epe_templ;
     struct epoll_event epe;
 
-    ASSERT(fd < ps->fds_status_len);
-
-    if (!need_update(ps, fd))
-	return 0;
-
-#ifdef ERTS_POLL_DEBUG_PRINT
-    erts_printf("Doing update on fd=%d\n", fd);
-#endif
-    if (ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK) {
-#if ERTS_POLL_USE_CONCURRENT_UPDATE
-	if (!*update_fallback) {
-	    *update_fallback = 1;
-	    return 0;
-	}
-#endif
-	if (ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_USEFLBCK) {
-	    return update_fallback_pollset(ps, fd);
-	}
-	else { /* Remove from fallback and try epoll */
-	    ErtsPollEvents events = ps->fds_status[fd].events;
-	    ps->fds_status[fd].events = (ErtsPollEvents) 0;
-	    res = update_fallback_pollset(ps, fd);
-	    ASSERT(!(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK));
-	    if (!events)
-		return res;
-	    ps->fds_status[fd].events = events;
-	}
-    }
-
-    epe_templ.events = ERTS_POLL_EV_E2N(ps->fds_status[fd].events);
+    epe_templ.events = ERTS_POLL_EV_E2N(events) | EPOLLONESHOT;
     epe_templ.data.fd = fd;
 
 #ifdef VALGRIND
@@ -1170,30 +678,24 @@ update_pollset(ErtsPollSet ps, int fd)
     memset((void *) &epe.data, 0, sizeof(epoll_data_t));
 #endif
 
-    if (epe_templ.events && ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_RST) {
-	do {
-	    /* We init 'epe' every time since epoll_ctl() may modify it
-	       (not declared const and not documented as const). */
-	    epe.events = epe_templ.events;
-	    epe.data.fd = epe_templ.data.fd;
-	    res = epoll_ctl(ps->kp_fd, EPOLL_CTL_DEL, fd, &epe);
-	} while (res != 0 && errno == EINTR);
-	erts_atomic_dec_nob(&ps->no_of_user_fds);
-	ps->fds_status[fd].used_events = 0;
-    }
-
-    if (!epe_templ.events) {
+    switch (op) {
+    case ERTS_POLL_OP_DEL:
 	/* A note on EPOLL_CTL_DEL: linux kernel versions before 2.6.9
 	   need a non-NULL event pointer even though it is ignored... */
-	op = EPOLL_CTL_DEL;
+        epoll_op = EPOLL_CTL_DEL;
+        epe_templ.events = 0;
 	erts_atomic_dec_nob(&ps->no_of_user_fds);
-    }
-    else if (!ps->fds_status[fd].used_events) {
-	op = EPOLL_CTL_ADD;
+        break;
+    case ERTS_POLL_OP_ADD:
+        epoll_op = EPOLL_CTL_ADD;
 	erts_atomic_inc_nob(&ps->no_of_user_fds);
-    }
-    else {
-	op = EPOLL_CTL_MOD;
+        break;
+    case ERTS_POLL_OP_MOD:
+        epoll_op = EPOLL_CTL_MOD;
+        break;
+    default:
+        ASSERT(0);
+        break;
     }
 
     do {
@@ -1201,33 +703,32 @@ update_pollset(ErtsPollSet ps, int fd)
 	   (not declared const and not documented as const). */
 	epe.events = epe_templ.events;
 	epe.data.fd = epe_templ.data.fd;
-	res = epoll_ctl(ps->kp_fd, op, fd, &epe);
+	res = epoll_ctl(ps->kp_fd, epoll_op, fd, &epe);
     } while (res != 0 && errno == EINTR);
 
-#if defined(ERTS_POLL_DEBUG_PRINT) && 1
+#if ERTS_POLL_DEBUG_PRINT
     {
 	int saved_errno = errno;
-	erts_printf("%s = epoll_ctl(%d, %s, %d, {Ox%x, %d})\n",
-		     res == 0 ? "0" : erl_errno_id(errno),
-		     ps->kp_fd,
-		     (op == EPOLL_CTL_ADD
-		      ? "EPOLL_CTL_ADD"
-		      : (op == EPOLL_CTL_MOD
-			 ? "EPOLL_CTL_MOD"
-			 : (op == EPOLL_CTL_DEL
-			    ? "EPOLL_CTL_DEL"
-			    : "UNKNOWN"))),
-		     fd,
-		     epe_templ.events,
-		     fd);
+	DEBUG_PRINT_FD("%s = epoll_ctl(%d, %s, %d, {0x%x, %d})",
+                       ps, fd,
+                       res == 0 ? "0" : erl_errno_id(errno),
+                       ps->kp_fd,
+                       (epoll_op == EPOLL_CTL_ADD
+                        ? "EPOLL_CTL_ADD"
+                        : (epoll_op == EPOLL_CTL_MOD
+                           ? "EPOLL_CTL_MOD"
+                           : (epoll_op == EPOLL_CTL_DEL
+                              ? "EPOLL_CTL_DEL"
+                              : "UNKNOWN"))),
+                       fd,
+                       epe_templ.events,
+                       fd);
 	errno = saved_errno;
     }
 #endif
-    if (res == 0)
-	ps->fds_status[fd].used_events = ps->fds_status[fd].events;
-    else {
+    if (res != 0) {
 	switch (op) {
-	case EPOLL_CTL_MOD:
+	case ERTS_POLL_OP_MOD:
 	    epe.events = 0;
 	    do {
 		/* We init 'epe' every time since epoll_ctl() may modify it
@@ -1236,29 +737,18 @@ update_pollset(ErtsPollSet ps, int fd)
 		epe.data.fd = fd;
 		res = epoll_ctl(ps->kp_fd, EPOLL_CTL_DEL, fd, &epe);
 	    } while (res != 0 && errno == EINTR);
-	    ps->fds_status[fd].used_events = 0;
 	/* Fall through ... */
-	case EPOLL_CTL_ADD: {
-	    ps->fds_status[fd].flags |= ERTS_POLL_FD_FLG_USEFLBCK;
+	case ERTS_POLL_OP_ADD: {
 	    erts_atomic_dec_nob(&ps->no_of_user_fds);
-#if ERTS_POLL_USE_CONCURRENT_UPDATE
-	    if (!*update_fallback) {
-		*update_fallback = 1;
-		return 0;
-	    }
-#endif
-	    ASSERT(!(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK));
-	    res = update_fallback_pollset(ps, fd);
-	    ASSERT(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK);
+            res = ERTS_POLL_EV_NVAL;
 	    break;
 	}
-	case EPOLL_CTL_DEL: {
+	case ERTS_POLL_OP_DEL: {
 	    /*
 	     * Since we use a lazy update approach EPOLL_CTL_DEL will
 	     * frequently fail. This since epoll automatically removes
 	     * a filedescriptor that is closed from the poll set.
 	     */
-	    ps->fds_status[fd].used_events = 0;
 	    res = 0;
 	    break;
 	}
@@ -1267,67 +757,277 @@ update_pollset(ErtsPollSet ps, int fd)
 			__FILE__, __LINE__);
 	    break;
 	}
+    } else {
+        res = events;
     }
-    ps->fds_status[fd].flags &= ~ERTS_POLL_FD_FLG_RST;
     return res;
 }
 
-#if ERTS_POLL_USE_CONCURRENT_UPDATE
+#endif /* ERTS_POLL_USE_EPOLL */
+
+#if ERTS_POLL_USE_KQUEUE
+
+/* Some versions of the EV_SET macro used kevp multiple times,
+   so we define out own version that make sure that it is safe
+   to do kevp++ in the argument list. */
+#define ERTS_EV_SET(kevp, a, b, c, f) do {              \
+        struct kevent *kevp_ = kevp;                    \
+        EV_SET(kevp_, a, b, c, 0, 0, f);                \
+    } while(0)
+
 static int
-update_pollset(ErtsPollSet ps, int fd)
+update_pollset(ErtsPollSet *ps, int fd, ErtsPollOp op, ErtsPollEvents events)
 {
-    int update_fallback = 1;
-    return conc_update_pollset(ps, fd, &update_fallback);
-}
-#endif
-
-#endif /* ERTS_POLL_USE_EPOLL */
+    int res = 0, len = 0;
+    struct kevent evts[2];
+    struct timespec ts = {0, 0};
 
-#endif /* ERTS_POLL_USE_BATCH_UPDATE_POLLSET */
+#ifdef EV_DISPATCH
+    /* If we have EV_DISPATCH we use it. The kevent descriptions for both
+       read and write are added on OP_ADD and removed on OP_DEL. And then
+       after than only EV_ENABLE|EV_DISPATCH are used.
+
+       It could be possible to not modify the pollset when disabling and/or
+       deleting events, but that may cause the poll threads to be awoken
+       a lot more than they should so we take the cost here instead of
+       in the poll thread.
+
+       Note: We need to have EV_DISPATCH both when the event is enabled and
+       disabled, as otherwise the event may be triggered twice on each re-arm.
+       Not sure if this is intended or not (can't find anything about it in the
+       man page), but it seems to be the way it works...
+    */
+
+    if (op == ERTS_POLL_OP_DEL) {
+        erts_atomic_dec_nob(&ps->no_of_user_fds);
+        /* We could probably skip this delete, do we want to? */
+        ERTS_EV_SET(&evts[len++], fd, EVFILT_READ, EV_DELETE, (void *) 0);
+        ERTS_EV_SET(&evts[len++], fd, EVFILT_WRITE, EV_DELETE, (void *) 0);
+    } else if (op == ERTS_POLL_OP_ADD) {
+        uint32_t flags;
+        erts_atomic_inc_nob(&ps->no_of_user_fds);
+
+        flags = EV_ADD|EV_DISPATCH;
+        flags |= ((events & ERTS_POLL_EV_IN) ? 0 : EV_DISABLE);
+        ERTS_EV_SET(&evts[len++], fd, EVFILT_READ, flags, (void *) ERTS_POLL_EV_IN);
+
+        flags = EV_ADD|EV_DISPATCH;
+        flags |= ((events & ERTS_POLL_EV_OUT) ? 0 : EV_DISABLE);
+        ERTS_EV_SET(&evts[len++], fd, EVFILT_WRITE, flags, (void *) ERTS_POLL_EV_OUT);
+    } else {
+        uint32_t flags;
+        ASSERT(op == ERTS_POLL_OP_MOD);
 
-#if ERTS_POLL_USE_POLL || ERTS_POLL_USE_SELECT || ERTS_POLL_USE_FALLBACK
+        flags = EV_DISPATCH;
+        flags |= (events & ERTS_POLL_EV_IN) ? EV_ENABLE : EV_DISABLE;
+        ERTS_EV_SET(&evts[len++], fd, EVFILT_READ, flags, (void *) ERTS_POLL_EV_IN);
 
-#if ERTS_POLL_USE_FALLBACK
-static int update_fallback_pollset(ErtsPollSet ps, int fd)
+        flags = EV_DISPATCH;
+        flags |= (events & ERTS_POLL_EV_OUT) ? EV_ENABLE : EV_DISABLE;
+        ERTS_EV_SET(&evts[len++], fd, EVFILT_WRITE, flags, (void *) ERTS_POLL_EV_OUT);
+    }
 #else
-static int update_pollset(ErtsPollSet ps, int fd)
+    uint32_t flags = EV_ADD|EV_ONESHOT;
+
+    if (op == ERTS_POLL_OP_DEL) {
+        erts_atomic_dec_nob(&ps->no_of_user_fds);
+        /* We don't do anything when a delete is issued. The fds will be removed
+           when they are triggered, or when they are closed. */
+        events = 0;
+    } else if (op == ERTS_POLL_OP_ADD) {
+        erts_atomic_inc_nob(&ps->no_of_user_fds);
+    }
+
+    if (events & ERTS_POLL_EV_IN) {
+        ERTS_EV_SET(&evts[len++], fd, EVFILT_READ, flags, (void *) ERTS_POLL_EV_IN);
+    }
+    if (events & ERTS_POLL_EV_OUT) {
+        ERTS_EV_SET(&evts[len++], fd, EVFILT_WRITE, flags, (void *) ERTS_POLL_EV_OUT);
+    }
+
 #endif
-{
-#ifdef ERTS_POLL_DEBUG_PRINT
-#if ERTS_POLL_USE_FALLBACK
-    erts_printf("Doing fallback update on fd=%d\n", fd);
+    if (len)
+        do {
+            res = kevent(ps->kp_fd, evts, len, NULL, 0, &ts);
+        } while (res < 0 && errno == EINTR);
+#if ERTS_POLL_DEBUG_PRINT
+    {
+        int saved_errno = errno, i;
+        char keventb[255], *keventbp = keventb;
+        if (res < 0)
+            keventbp += sprintf(keventbp,"%s = ",erl_errno_id(saved_errno));
+        else
+            keventbp += sprintf(keventbp,"%d = ",res);
+        keventbp += sprintf(keventbp, "kevent(%d, {",ps->kp_fd);
+        for (i = 0; i < len; i++) {
+            const char *flags = "UNKNOWN";
+            if (evts[i].flags == EV_DELETE) flags = "EV_DELETE";
+            if (evts[i].flags == (EV_ADD|EV_ONESHOT)) flags = "EV_ADD|EV_ONESHOT";
+#ifdef EV_DISPATCH
+            if (evts[i].flags == (EV_ADD|EV_DISPATCH)) flags = "EV_ADD|EV_DISPATCH";
+            if (evts[i].flags == (EV_ADD|EV_DISABLE)) flags = "EV_ADD|EV_DISABLE";
+            if (evts[i].flags == (EV_ENABLE|EV_DISPATCH)) flags = "EV_ENABLE|EV_DISPATCH";
+            if (evts[i].flags == EV_DISABLE) flags = "EV_DISABLE";
+            if (evts[i].flags == (EV_DISABLE|EV_DISPATCH)) flags = "EV_DISABLE|EV_DISABLE";
+#endif
+
+            keventbp += sprintf(keventbp, "%s{%lu, %s, %s}",i > 0 ? ", " : "",
+                                evts[i].ident,
+                                (evts[i].filter == EVFILT_READ
+                                 ? "EVFILT_READ"
+                                 : (evts[i].filter == EVFILT_WRITE
+                                    ? "EVFILT_WRITE"
+                                    : "UNKNOWN")), flags);
+        }
+        keventbp += sprintf(keventbp, "}, %d)", len);
+        DEBUG_PRINT_FD("%s", ps, fd, keventb);
+        errno = saved_errno;
+    }
+#endif
+    if (res < 0) {
+        if (op != ERTS_POLL_OP_DEL) {
+#ifdef EV_RECEIPT
+            struct kevent receipt_evts[2];
+            len = 0;
+            ERTS_EV_SET(&evts[len++], fd, EVFILT_WRITE, EV_DELETE|EV_RECEIPT, (void *) 0);
+            ERTS_EV_SET(&evts[len++], fd, EVFILT_READ, EV_DELETE|EV_RECEIPT, (void *) 0);
+            do {
+                res = kevent(ps->kp_fd, evts, len, receipt_evts, 2, &ts);
+            } while (res < 0 && errno == EINTR);
 #else
-    erts_printf("Doing update on fd=%d\n", fd);
+            ERTS_EV_SET(&evts[0], fd, EVFILT_WRITE, EV_DELETE, (void *) 0);
+            do {
+                res = kevent(ps->kp_fd, evts, 1, NULL, 0, &ts);
+            } while (res < 0 && errno == EINTR);
+            ERTS_EV_SET(&evts[0], fd, EVFILT_READ, EV_DELETE, (void *) 0);
+            do {
+                res = kevent(ps->kp_fd, evts, 1, NULL, 0, &ts);
+            } while (res < 0 && errno == EINTR);
+#endif
+            if (op == ERTS_POLL_OP_ADD)
+                erts_atomic_dec_nob(&ps->no_of_user_fds);
+            events = ERTS_POLL_EV_NVAL;
+        } else
+            events = 0;
+    }
+    return events;
+}
+
+#endif /* ERTS_POLL_USE_KQUEUE */
+
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
+
+static ERTS_INLINE void
+init_batch_update(ErtsPollSet *ps, int len)
+{
+#if ERTS_POLL_USE_DEVPOLL
+    ASSERT(ps->poll_fds == NULL);
+    ps->poll_fds = erts_alloc(ERTS_ALC_T_TMP, sizeof(struct pollfd) * len);
+    ps->poll_fds_ix = 0;
 #endif
+}
+
+static ERTS_INLINE void
+write_batch_update(ErtsPollSet *ps)
+{
+#if ERTS_POLL_USE_DEVPOLL
+    ssize_t wres;
+    char *buf = (char *) ps->poll_fds;
+    size_t buf_size = sizeof(struct pollfd)*ps->poll_fds_ix;
+
+    while (1) {
+	wres = write(ps->kp_fd, (void *) buf, buf_size);
+	if (wres < 0) {
+	    if (errno == EINTR)
+		continue;
+	    fatal_error("%s:%d:write_batch_buf(): "
+			"Failed to write to /dev/poll: "
+			"%s (%d)\n",
+			__FILE__, __LINE__,
+			erl_errno_id(errno), errno);
+	}
+#if ERTS_POLL_DEBUG_PRINT
+        {
+            int saved_errno = errno, i;
+            char devpollb[2048], *devpollbp = devpollb;
+            devpollbp += sprintf(devpollbp, "%d = devpoll(%d, {", wres, ps->kp_fd);
+            for (i = 0; i < wres / sizeof(struct pollfd); i++) {
+                if (devpollbp == devpollb)
+                    devpollbp += sprintf(devpollbp, "%d = devpoll(%d, {", wres, ps->kp_fd);
+                devpollbp += sprintf(devpollbp, "%s{fd = %d, events = %s}",
+                                     i > 0 ? ", " : "",
+                                     ps->poll_fds[i].fd,
+                                     ev2str(ps->poll_fds[i].events));
+                if (devpollbp - devpollb > 512) {
+                    devpollbp += sprintf(devpollbp, "}, %d)", ps->poll_fds_ix);
+                    DEBUG_PRINT("%s", ps, devpollb);
+                    devpollbp = devpollb;
+                }
+            }
+            devpollbp += sprintf(devpollbp, "}, %d)", ps->poll_fds_ix);
+            DEBUG_PRINT("%s", ps, devpollb);
+            errno = saved_errno;
+        }
 #endif
 
-    ASSERT(fd < ps->fds_status_len);
-#if ERTS_POLL_USE_FALLBACK
-    ASSERT(ps->fds_status[fd].used_events
-	   ? (ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK)
-	   : (ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_USEFLBCK));
+	buf_size -= wres;
+	if (buf_size <= 0)
+	    break;
+	buf += wres;
+    }
+
+    if (buf_size < 0) {
+	fatal_error("%s:%d:write_devpoll_buf(): Internal error\n",
+		    __FILE__, __LINE__);
+    }
+    erts_free(ERTS_ALC_T_TMP, ps->poll_fds);
+    ps->poll_fds = NULL;
 #endif
+}
 
-    if (!need_update(ps, fd))
-	return 0;
+static ERTS_INLINE int
+need_update(ErtsPollSet *ps, int fd, int *resetp)
+{
+    int reset;
+    ASSERT(fd < ps->fds_status_len);
 
-#if ERTS_POLL_USE_FALLBACK
+    reset = (int) (ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_RST);
     ps->fds_status[fd].flags &= ~ERTS_POLL_FD_FLG_RST;
-#endif
+
+    *resetp = reset;
+
+    if (reset || ps->fds_status[fd].used_events != ps->fds_status[fd].events)
+	return 1;
+
+    return 0;
+}
+
+static int update_pollset(ErtsPollSet *ps, ErtsPollResFd pr[], int fd)
+{
+    int res = 0, reset = 0;
+    ErtsPollEvents events = ps->fds_status[fd].events;
+    ASSERT(fd < ps->fds_status_len);
+
+    if (!need_update(ps, fd, &reset))
+	return res;
 
 #if ERTS_POLL_USE_POLL	/* --- poll -------------------------------- */
-    if (!ps->fds_status[fd].events) {
+    if (!events) {
 	int pix = ps->fds_status[fd].pix;
 	int last_pix;
+
+        if (reset) {
+            /* When a fd has been reset, we tell the caller of erts_poll_wait
+               this by setting the fd as ERTS_POLL_EV_NONE */
+            ERTS_POLL_RES_SET_FD(&pr[res], fd);
+            ERTS_POLL_RES_SET_EVTS(&pr[res], ERTS_POLL_EV_NONE);
+            DEBUG_PRINT_FD("trig %s (poll)", ps, fd, ev2str(ERTS_POLL_EV_NONE));
+            res++;
+        }
+
 	if (pix < 0) {
-#if ERTS_POLL_USE_FALLBACK
-	    ASSERT(!(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK));
-#endif
-	    return -1;
+	    return res;
 	}
-#if ERTS_POLL_USE_FALLBACK
-	ASSERT(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK);
-#endif
 	erts_atomic_dec_nob(&ps->no_of_user_fds);
 	last_pix = --ps->no_poll_fds;
 	if (pix != last_pix) {
@@ -1344,126 +1044,151 @@ static int update_pollset(ErtsPollSet ps, int fd)
 	/* Clear this fd status */
 	ps->fds_status[fd].pix = -1;
 	ps->fds_status[fd].used_events = (ErtsPollEvents) 0;
-#if ERTS_POLL_USE_FALLBACK
-	ps->fds_status[fd].flags &= ~ERTS_POLL_FD_FLG_INFLBCK;
-#endif
+
     }
     else {
 	int pix = ps->fds_status[fd].pix;
 	if (pix < 0) {
-#if ERTS_POLL_USE_FALLBACK
-	    ASSERT(!(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK)
-		    || fd == ps->kp_fd);
-#endif
 	    erts_atomic_inc_nob(&ps->no_of_user_fds);
 	    ps->fds_status[fd].pix = pix = ps->no_poll_fds++;
 	    if (pix >= ps->poll_fds_len)
 		grow_poll_fds(ps, pix);
 	    ps->poll_fds[pix].fd = fd;
 	    ps->fds_status[fd].pix = pix;
-#if ERTS_POLL_USE_FALLBACK
-	    ps->fds_status[fd].flags |= ERTS_POLL_FD_FLG_INFLBCK;
-#endif
 	}
 
-#if ERTS_POLL_USE_FALLBACK
-	ASSERT(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK);
-#endif
-
 	/* Events to be used in next poll */
-	ps->poll_fds[pix].events = ev2pollev(ps->fds_status[fd].events);
+	ps->poll_fds[pix].events = ev2pollev(events);
 	if (ps->poll_fds[pix].revents) {
 	    /* Remove result events that we should not poll for anymore */
 	    ps->poll_fds[pix].revents
 		&= ev2pollev(~(~ps->fds_status[fd].used_events
-			       & ps->fds_status[fd].events));
+			       & events));
 	}
 	/* Save events to be used in next poll */
-	ps->fds_status[fd].used_events = ps->fds_status[fd].events;
+	ps->fds_status[fd].used_events = events;
     }
-    return 0;
+    return res;
 #elif ERTS_POLL_USE_SELECT	/* --- select ------------------------------ */
-    {
-	ErtsPollEvents events = ps->fds_status[fd].events;
+    if (!events) {
+
+        if (reset) {
+            /* When a fd has been reset, we tell the caller of erts_poll_wait
+               this by setting the fd as ERTS_POLL_EV_NONE */
+            ERTS_POLL_RES_SET_FD(&pr[res], fd);
+            ERTS_POLL_RES_SET_EVTS(&pr[res], ERTS_POLL_EV_NONE);
+            DEBUG_PRINT_FD("trig %s (select)", ps, fd, ev2str(ERTS_POLL_EV_NONE));
+            res++;
+        }
+
+        ERTS_FD_CLR(fd, &ps->input_fds);
+        ERTS_FD_CLR(fd, &ps->output_fds);
+
+        if (ps->fds_status[fd].used_events) {
+            erts_atomic_dec_nob(&ps->no_of_user_fds);
+            ps->fds_status[fd].used_events = (ErtsPollEvents) 0;
+        }
+
+        if (fd == ps->max_fd) {
+            int max = ps->max_fd;
+            for (max = ps->max_fd; max >= 0; max--)
+                if (ps->fds_status[max].used_events)
+                    break;
+            ps->max_fd = max;
+        }
+
+    } else {
+
 	ensure_select_fds(fd, &ps->input_fds, &ps->output_fds);
-	if ((ERTS_POLL_EV_IN & events)
-	    != (ERTS_POLL_EV_IN & ps->fds_status[fd].used_events)) {
-	    if (ERTS_POLL_EV_IN & events) {
-		ERTS_FD_SET(fd, &ps->input_fds);
-	    }
-	    else {
-		ERTS_FD_CLR(fd, &ps->input_fds);
-	    }
-	}
-	if ((ERTS_POLL_EV_OUT & events)
-	    != (ERTS_POLL_EV_OUT & ps->fds_status[fd].used_events)) {
-	    if (ERTS_POLL_EV_OUT & events) {
-		ERTS_FD_SET(fd, &ps->output_fds);
-	    }
-	    else {
-		ERTS_FD_CLR(fd, &ps->output_fds);
-	    }
-	}
 
-	if (!ps->fds_status[fd].used_events) {
-	    ASSERT(events);
-	    erts_atomic_inc_nob(&ps->no_of_user_fds);
-#if ERTS_POLL_USE_FALLBACK
-	    ps->no_select_fds++;
-	    ps->fds_status[fd].flags |= ERTS_POLL_FD_FLG_INFLBCK;
-#endif
-	}
-	else if (!events) {
-	    ASSERT(ps->fds_status[fd].used_events);
-	    erts_atomic_dec_nob(&ps->no_of_user_fds);
-	    ps->fds_status[fd].events = events;
-#if ERTS_POLL_USE_FALLBACK
-	    ps->no_select_fds--;
-	    ps->fds_status[fd].flags &= ~ERTS_POLL_FD_FLG_INFLBCK;
-#endif
-	}
+        if (!ps->fds_status[fd].used_events)
+            erts_atomic_inc_nob(&ps->no_of_user_fds);
+
+        if (events & ERTS_POLL_EV_IN)
+            ERTS_FD_SET(fd, &ps->input_fds);
+        else
+            ERTS_FD_CLR(fd, &ps->input_fds);
+
+        if (events & ERTS_POLL_EV_OUT)
+            ERTS_FD_SET(fd, &ps->output_fds);
+        else
+            ERTS_FD_CLR(fd, &ps->output_fds);
 
 	ps->fds_status[fd].used_events = events;
 
-	if (events && fd > ps->max_fd)
-	    ps->max_fd = fd;
-	else if (!events && fd == ps->max_fd) {
-	    int max = ps->max_fd;
-	    for (max = ps->max_fd; max >= 0; max--)
-		if (ps->fds_status[max].used_events)
-		    break;
-	    ps->max_fd = max;
-	}
+        if (fd > ps->max_fd)
+            ps->max_fd = fd;
     }
-    return 0;
-#endif
-}
 
-#endif /* ERTS_POLL_USE_POLL || ERTS_POLL_USE_SELECT || ERTS_POLL_USE_FALLBACK */
+    return res;
+#elif ERTS_POLL_USE_DEVPOLL
+
+    if (!events) {
 
+        if (reset) {
+            /* When a fd has been reset, we tell the caller of erts_poll_wait
+               this by setting the fd as ERTS_POLL_EV_NONE */
+            ERTS_POLL_RES_SET_FD(&pr[res], fd);
+            ERTS_POLL_RES_SET_EVTS(&pr[res], ERTS_POLL_EV_NONE);
+            DEBUG_PRINT_FD("trig %s (devpoll)", ps, fd, ev2str(ERTS_POLL_EV_NONE));
+            res++;
+        }
 
-static void
-handle_update_requests(ErtsPollSet ps)
-{
-    ErtsPollSetUpdateRequestsBlock *urqbp = &ps->update_requests;
-#if ERTS_POLL_USE_BATCH_UPDATE_POLLSET
-    ErtsPollBatchBuf bb;
-    setup_batch_buf(ps, &bb);
+        ps->poll_fds[ps->poll_fds_ix].fd = fd;
+        ps->poll_fds[ps->poll_fds_ix].revents = 0;
+        ps->poll_fds[ps->poll_fds_ix++].events = POLLREMOVE;
+
+        if (ps->fds_status[fd].used_events) {
+            erts_atomic_dec_nob(&ps->no_of_user_fds);
+            ps->fds_status[fd].used_events = 0;
+        }
+
+    } else {
+        if (!ps->fds_status[fd].used_events) {
+            erts_atomic_inc_nob(&ps->no_of_user_fds);
+        }
+        ps->poll_fds[ps->poll_fds_ix].fd = fd;
+        ps->poll_fds[ps->poll_fds_ix].revents = 0;
+        ps->poll_fds[ps->poll_fds_ix++].events = ERTS_POLL_EV_E2N(events);
+        ps->fds_status[fd].used_events = ps->fds_status[fd].events;
+    }
+
+    return res;
 #endif
+}
+
+static int
+handle_update_requests(ErtsPollSet *ps, ErtsPollResFd pr[], int no_fds)
+{
+    int res = 0;
+    ErtsPollSetUpdateRequestsBlock *urqbp = ps->curr_upd_req_block;
 
     while (urqbp) {
 	ErtsPollSetUpdateRequestsBlock *free_urqbp = urqbp;
 	int i;
 	int len = urqbp->len;
+
+        init_batch_update(ps, len);
+
 	for (i = 0; i < len; i++) {
 	    int fd = urqbp->fds[i];
 	    ASSERT(fd < ps->fds_status_len);
-	    ps->fds_status[fd].flags &= ~ERTS_POLL_FD_FLG_INURQ;
-#if ERTS_POLL_USE_BATCH_UPDATE_POLLSET
-	    batch_update_pollset(ps, fd, &bb);
-#else
-	    update_pollset(ps, fd);
-#endif
+            ASSERT(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INURQ);
+
+            /* We have run out of PollResFd slots to put results in,
+               so we yield here and return later for more. */
+            if (res == no_fds && pr != NULL) {
+                memmove(urqbp->fds, urqbp->fds+i, sizeof(int) * (len - i));
+                urqbp->len -= i;
+                ps->curr_upd_req_block = urqbp;
+                write_batch_update(ps);
+                return res;
+            }
+
+            if (ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INURQ) {
+                ps->fds_status[fd].flags &= ~ERTS_POLL_FD_FLG_INURQ;
+                res += update_pollset(ps, pr + res, fd);
+            }
 	}
 
 	free_urqbp = urqbp;
@@ -1471,12 +1196,9 @@ handle_update_requests(ErtsPollSet ps)
 
 	free_update_requests_block(ps, free_urqbp);
 
-    }
+        write_batch_update(ps);
 
-#if ERTS_POLL_USE_BATCH_UPDATE_POLLSET
-    if (bb.len)
-	write_batch_buf(ps, &bb);
-#endif
+    }
 
     ps->curr_upd_req_block = &ps->update_requests;
 
@@ -1485,16 +1207,19 @@ handle_update_requests(ErtsPollSet ps)
 #endif
 
     ERTS_POLLSET_UNSET_HAVE_UPDATE_REQUESTS(ps);
+    return res;
 }
 
+#endif /* !ERTS_POLL_USE_CONCURRENT_UPDATE */
 
 static ERTS_INLINE ErtsPollEvents
-poll_control(ErtsPollSet ps, int fd, ErtsPollEvents events, int on, int *do_wake)
+poll_control(ErtsPollSet *ps, int fd, ErtsPollOp op,
+             ErtsPollEvents events, int *do_wake)
 {
     ErtsPollEvents new_events;
 
     if (fd < ps->internal_fd_limit || fd >= max_fds) {
-	if (fd < 0) {
+	if (fd < 0 || fd >= max_fds) {
 	    new_events = ERTS_POLL_EV_ERR;
 	    goto done;
 	}
@@ -1504,115 +1229,55 @@ poll_control(ErtsPollSet ps, int fd, ErtsPollEvents events, int on, int *do_wake
 	    goto done;
 	}
 #endif
+#if ERTS_POLL_USE_WAKEUP_PIPE
 	if (fd == ps->wake_fds[0] || fd == ps->wake_fds[1]) {
 	    new_events = ERTS_POLL_EV_NVAL;
 	    goto done;
 	}
-#if ERTS_POLL_USE_TIMERFD
-	if (fd == ps->timer_fd) {
-	    new_events = ERTS_POLL_EV_NVAL;
-	    goto done;
-	}
 #endif
     }
 
+#if ERTS_POLL_USE_CONCURRENT_UPDATE
+
+    new_events = update_pollset(ps, fd, op, events);
+
+#else /* !ERTS_POLL_USE_CONCURRENT_UPDATE */
     if (fd >= ps->fds_status_len)
 	grow_fds_status(ps, fd);
 
     ASSERT(fd < ps->fds_status_len);
 
-    new_events = ps->fds_status[fd].events;
-
-    if (events == 0) {
-	*do_wake = 0;
-	goto done;
-    }
-
-    if (on)
-	new_events |= events;
-    else
-	new_events &= ~events;
-
-    if (new_events == (ErtsPollEvents) 0) {
-	ps->fds_status[fd].flags |= ERTS_POLL_FD_FLG_RST;
-#if ERTS_POLL_USE_FALLBACK
-	ps->fds_status[fd].flags &= ~ERTS_POLL_FD_FLG_USEFLBCK;
-#endif
-    }
-
-    ps->fds_status[fd].events = new_events;
-
-    if (new_events == ps->fds_status[fd].used_events
-	&& !(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_RST)
-	) {
-	*do_wake = 0;
-	goto done;
-    }
-
-
-#if ERTS_POLL_USE_CONCURRENT_UPDATE
-    if (ERTS_POLLSET_IS_POLLED(ps)) {
-	int update_fallback = 0;
-	conc_update_pollset(ps, fd, &update_fallback);
-	if (!update_fallback) {
-	    *do_wake = 0; /* no need to wake kernel poller */
-	    goto done;
-	}
+    if (op == ERTS_POLL_OP_DEL) {
+        ps->fds_status[fd].flags |= ERTS_POLL_FD_FLG_RST;
+        ps->fds_status[fd].events = 0;
+        *do_wake = 1;
+    } else if (op == ERTS_POLL_OP_ADD) {
+        ASSERT(ps->fds_status[fd].events == 0);
+        ps->fds_status[fd].events = events;
+        *do_wake = 1;
+    } else {
+        ASSERT(op == ERTS_POLL_OP_MOD);
+        ps->fds_status[fd].events = events;
+        *do_wake = 1;
     }
-#endif
+    new_events = ps->fds_status[fd].events;
 
     enqueue_update_request(ps, fd);
-	
-    /*
-     * If new events have been added, we need to wake up the
-     * polling thread, but if events have been removed we don't.
-     */
-    if ((new_events && (ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_RST))
-	|| (~ps->fds_status[fd].used_events & new_events))
-	*do_wake = 1;
 
+#endif /* !ERTS_POLL_USE_CONCURRENT_UPDATE */
 
  done:
-#ifdef ERTS_POLL_DEBUG_PRINT
-     erts_printf("0x%x = poll_control(ps, %d, 0x%x, %s) do_wake=%d\n",
-		 (int) new_events, fd, (int) events, (on ? "on" : "off"), *do_wake);
-#endif
+    DEBUG_PRINT_FD("%s = %s(%p, %d, %s, %s) do_wake=%d",
+                   ps, fd, ev2str(new_events), __FUNCTION__, ps,
+                   fd, op2str(op), ev2str(events), *do_wake);
     return new_events;
 }
 
-void
-ERTS_POLL_EXPORT(erts_poll_controlv)(ErtsPollSet ps,
-				     ErtsPollControlEntry pcev[],
-				     int len)
-{
-    int i;
-    int do_wake;
-    int final_do_wake = 0;
-
-    ERTS_POLLSET_LOCK(ps);
-
-    for (i = 0; i < len; i++) {
-	do_wake = 0;
-	pcev[i].events = poll_control(ps,
-				      pcev[i].fd,
-				      pcev[i].events,
-				      pcev[i].on,
-				      &do_wake);
-	final_do_wake |= do_wake;
-    }
-
-    ERTS_POLLSET_UNLOCK(ps);
-
-    if (final_do_wake)
-	wake_poller(ps, 0, 0);
-
-}
-
 ErtsPollEvents
-ERTS_POLL_EXPORT(erts_poll_control)(ErtsPollSet ps,
+ERTS_POLL_EXPORT(erts_poll_control)(ErtsPollSet *ps,
 				    ErtsSysFdType fd,
+                                    ErtsPollOp op,
 				    ErtsPollEvents events,
-				    int on,
 				    int* do_wake) /* In: Wake up polling thread */
 				                  /* Out: Poller is woken */
 {
@@ -1620,13 +1285,15 @@ ERTS_POLL_EXPORT(erts_poll_control)(ErtsPollSet ps,
 
     ERTS_POLLSET_LOCK(ps);
 
-    res = poll_control(ps, fd, events, on, do_wake);
+    res = poll_control(ps, fd, op, events, do_wake);
 
     ERTS_POLLSET_UNLOCK(ps);
 
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
     if (*do_wake) {
-	wake_poller(ps, 0, 0);
+	wake_poller(ps, 0);
     }
+#endif
 
     return res;
 }
@@ -1638,180 +1305,64 @@ ERTS_POLL_EXPORT(erts_poll_control)(ErtsPollSet ps,
 #if ERTS_POLL_USE_KERNEL_POLL
 
 static ERTS_INLINE int
-save_kp_result(ErtsPollSet ps, ErtsPollResFd pr[], int max_res, int chk_fds_res)
+ERTS_POLL_EXPORT(save_result)(ErtsPollSet *ps, ErtsPollResFd pr[], int max_res, int chk_fds_res, int ebadf)
 {
-    int res = 0;
-    int i;
-    int n = chk_fds_res < max_res ? chk_fds_res : max_res;
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE || ERTS_POLL_DEBUG_PRINT || ERTS_POLL_USE_WAKEUP_PIPE
+    int n = chk_fds_res < max_res ? chk_fds_res : max_res, i;
+    int res = n;
+#if ERTS_POLL_USE_WAKEUP_PIPE
     int wake_fd = ps->wake_fds[0];
-#if ERTS_POLL_USE_TIMERFD
-    int timer_fd = ps->timer_fd;
 #endif
 
     for (i = 0; i < n; i++) {
-
-#if ERTS_POLL_USE_EPOLL		/* --- epoll ------------------------------- */
-
-	if (ps->res_events[i].events) {
-	    int fd = ps->res_events[i].data.fd;
-	    int ix;
-	    ErtsPollEvents revents;
-	    if (fd == wake_fd) {
-		cleanup_wakeup_pipe(ps);
-		continue;
-	    }
-#if ERTS_POLL_USE_TIMERFD
-            if (fd == timer_fd) {
-                continue;
-            }
-#endif
-	    ASSERT(!(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK));
-	    /* epoll_wait() can repeat the same fd in result array... */
-	    ix = (int) ps->fds_status[fd].res_ev_ix;
-	    ASSERT(ix >= 0);
-	    if (ix >= res || pr[ix].fd != fd) {
-		ix = res;
-		pr[ix].fd = fd;
-		pr[ix].events = (ErtsPollEvents) 0;
-	    }
-
-	    revents = ERTS_POLL_EV_N2E(ps->res_events[i].events);
-	    pr[ix].events |= revents;
-	    if (revents) {
-		if (res == ix) {
-		    ps->fds_status[fd].res_ev_ix = (unsigned short) ix;
-		    res++;
-		}
-	    }
-	}
-
-#elif ERTS_POLL_USE_KQUEUE	/* --- kqueue ------------------------------ */
-
-	struct kevent *ev;
-	int fd;
-	int ix;
-
-	ev = &ps->res_events[i];
-	fd = (int) ev->ident;
-	ASSERT(fd < ps->fds_status_len);
-	ASSERT(!(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK));
-	ix = (int) ps->fds_status[fd].res_ev_ix;
-
-	ASSERT(ix >= 0);
-	if (ix >= res || pr[ix].fd != fd) {
-	    ix = res;
-	    pr[ix].fd = (int) ev->ident;
-	    pr[ix].events = (ErtsPollEvents) 0;
-	}
-
-	if (ev->filter == EVFILT_READ) {
-	    if (fd == wake_fd) {
-		cleanup_wakeup_pipe(ps);
-		continue;
-	    }
-	    pr[ix].events |= ERTS_POLL_EV_IN;
-	}
-	else if (ev->filter == EVFILT_WRITE)
-	    pr[ix].events |= ERTS_POLL_EV_OUT;
-	if (ev->flags & (EV_ERROR|EV_EOF)) {
-	    if ((ev->flags & EV_ERROR) && (((int) ev->data) == EBADF))
-		pr[ix].events |= ERTS_POLL_EV_NVAL;
-	    else
-		pr[ix].events |= ERTS_POLL_EV_ERR;
-	}
-	if (pr[ix].events) {
-	    if (res == ix) {
-		ps->fds_status[fd].res_ev_ix = (unsigned short) ix;
-		res++;
-	    }
-	}
-
-#elif ERTS_POLL_USE_DEVPOLL	/* --- devpoll ----------------------------- */
-
-	if (ps->res_events[i].revents) {
-	    int fd = ps->res_events[i].fd;
-	    ErtsPollEvents revents;
-	    if (fd == wake_fd) {
-		cleanup_wakeup_pipe(ps);
-		continue;
-	    }
-#if ERTS_POLL_USE_TIMERFD
-	    if (fd == timer_fd) {
-		continue;
-	    }
-#endif
-	    revents = ERTS_POLL_EV_N2E(ps->res_events[i].events);
-	    pr[res].fd = fd;
-	    pr[res].events = revents;
-	    res++;
-	}
-
+        int fd = ERTS_POLL_RES_GET_FD(&pr[i]);
+#ifdef DEBUG_PRINT_MODE
+        ErtsPollEvents evts = ERTS_POLL_RES_GET_EVTS(pr+i);
 #endif
 
-    }
-
-    return res;
-}
-
-#endif /* ERTS_POLL_USE_KERNEL_POLL */
-
-#if ERTS_POLL_USE_FALLBACK
-
-static int
-get_kp_results(ErtsPollSet ps, ErtsPollResFd pr[], int max_res)
-{
-    int res;
+        DEBUG_PRINT_FD("trig %s (%s)", ps, fd,
+                       ev2str(evts),
 #if ERTS_POLL_USE_KQUEUE
-    struct timespec ts = {0, 0};
+                       "kqueue"
+#elif ERTS_POLL_USE_EPOLL
+                       "epoll"
+#else
+                       "/dev/poll"
 #endif
+            );
 
-    if (max_res > ps->res_events_len)
-	grow_res_events(ps, max_res);
-
-    do {
-#if ERTS_POLL_USE_EPOLL
-	res = epoll_wait(ps->kp_fd, ps->res_events, max_res, 0);
-#elif ERTS_POLL_USE_KQUEUE
-	res = kevent(ps->kp_fd, NULL, 0, ps->res_events, max_res, &ts);
+#if ERTS_POLL_USE_WAKEUP_PIPE
+        if (fd == wake_fd) {
+            cleanup_wakeup_pipe(ps);
+            ERTS_POLL_RES_SET_EVTS(&pr[i], ERTS_POLL_EV_NONE);
+            if (n == 1)
+                return 0;
+        }
 #endif
-    } while (res < 0 && errno == EINTR);
-
-    if (res < 0) {
-	fatal_error("%s:%d: %s() failed: %s (%d)\n",
-		    __FILE__, __LINE__,
-#if ERTS_POLL_USE_EPOLL
-		    "epoll_wait",
-#elif ERTS_POLL_USE_KQUEUE
-		    "kevent",
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
+        else {
+            /* Reset the events to emulate ONESHOT semantics */
+            ps->fds_status[fd].events = 0;
+            enqueue_update_request(ps, fd);
+        }
 #endif
-		    erl_errno_id(errno), errno);
     }
 
-    return save_kp_result(ps, pr, max_res, res);
+    return res;
+#else
+    ASSERT(chk_fds_res <= max_res);
+    return chk_fds_res;
+#endif
 }
 
-#endif /* ERTS_POLL_USE_FALLBACK */
-
-
+#else /* !ERTS_POLL_USE_KERNEL_POLL */
 
 static ERTS_INLINE int
-save_poll_result(ErtsPollSet ps, ErtsPollResFd pr[], int max_res,
-		 int chk_fds_res, int ebadf)
+ERTS_POLL_EXPORT(save_result)(ErtsPollSet *ps, ErtsPollResFd pr[], int max_res, int chk_fds_res, int ebadf)
 {
-#if ERTS_POLL_USE_DEVPOLL
-    return save_kp_result(ps, pr, max_res, chk_fds_res);
-#elif ERTS_POLL_USE_FALLBACK
-    if (!ps->fallback_used)
-	return save_kp_result(ps, pr, max_res, chk_fds_res);
-    else
-#endif /* ERTS_POLL_USE_FALLBACK */
-    {
-
 #if ERTS_POLL_USE_POLL	/* --- poll -------------------------------- */
 	int res = 0;
-#if !ERTS_POLL_USE_FALLBACK
 	int wake_fd = ps->wake_fds[0];
-#endif
 	int i, first_ix, end_ix;
 
 	/*
@@ -1828,23 +1379,30 @@ save_poll_result(ErtsPollSet ps, ErtsPollResFd pr[], int max_res,
 		if (ps->poll_fds[i].revents != (short) 0) {
 		    int fd = ps->poll_fds[i].fd;
 		    ErtsPollEvents revents;
-#if ERTS_POLL_USE_FALLBACK
-		    if (fd == ps->kp_fd) {
-			res += get_kp_results(ps, &pr[res], max_res-res);
-			i++;
-			continue;
-		    }
-#else
 		    if (fd == wake_fd) {
 			cleanup_wakeup_pipe(ps);
 			i++;
 			continue;
 		    }
-#endif
 		    revents = pollev2ev(ps->poll_fds[i].revents);
-		    pr[res].fd = fd;
-		    pr[res].events = revents;
+		    ERTS_POLL_RES_SET_FD(&pr[res], fd);
+		    ERTS_POLL_RES_SET_EVTS(&pr[res], revents);
+
+                    /* If an fd returns as error, we may want to check the
+                       update_requests queue to see if it has been reset
+                       before delivering the result?!?! This should allow
+                       the user to do driver_dselect + close without waiting
+                       for stop_select... */
+
+                    DEBUG_PRINT_FD("trig %s (poll)", ps, ERTS_POLL_RES_GET_FD(&pr[res]),
+                                   ev2str(ERTS_POLL_RES_GET_EVTS(&pr[res])));
+
 		    res++;
+
+                    /* Clear the events for this fd in order to mimic
+                       how epoll ONESHOT works */
+                    ps->fds_status[fd].events = 0;
+                    enqueue_update_request(ps, fd);
 		}
 		i++;
 	    }
@@ -1860,9 +1418,7 @@ save_poll_result(ErtsPollSet ps, ErtsPollResFd pr[], int max_res,
 
 #elif ERTS_POLL_USE_SELECT	/* --- select ------------------------------ */
 	int res = 0;
-#if !ERTS_POLL_USE_FALLBACK
 	int wake_fd = ps->wake_fds[0];
-#endif
 	int fd, first_fd, end_fd;
 
 	/*
@@ -1875,29 +1431,23 @@ save_poll_result(ErtsPollSet ps, ErtsPollResFd pr[], int max_res,
 	if (!ebadf) {
 	    while (1) {
 		while (fd < end_fd && res < max_res) {
-
-		    pr[res].events = (ErtsPollEvents) 0;
+                    ErtsPollEvents events = 0;
 		    if (ERTS_FD_ISSET(fd, &ps->res_input_fds)) {
-#if ERTS_POLL_USE_FALLBACK
-			if (fd == ps->kp_fd) {
-			    res += get_kp_results(ps, &pr[res], max_res-res);
-			    fd++;
-			    continue;
-			}
-#else
 			if (fd == wake_fd) {
 			    cleanup_wakeup_pipe(ps);
 			    fd++;
 			    continue;
 			}
-#endif
-			pr[res].events |= ERTS_POLL_EV_IN;
+			events |= ERTS_POLL_EV_IN;
 		    }
 		    if (ERTS_FD_ISSET(fd, &ps->res_output_fds))
-			pr[res].events |= ERTS_POLL_EV_OUT;
-		    if (pr[res].events) {
-			pr[res].fd = fd;
+			events |= ERTS_POLL_EV_OUT;
+		    if (events) {
+                        ERTS_POLL_RES_SET_FD(&pr[res], fd);
+                        ERTS_POLL_RES_SET_EVTS(&pr[res], events);
 			res++;
+                        ps->fds_status[fd].events = 0;
+                        enqueue_update_request(ps, fd);
 		    }
 		    fd++;
 		}
@@ -1930,7 +1480,7 @@ save_poll_result(ErtsPollSet ps, ErtsPollResFd pr[], int max_res,
 			if (ps->fds_status[fd].events & ERTS_POLL_EV_OUT) {
 			    oset = &ps->res_output_fds;
 			    ERTS_FD_ZERO(oset);
-			    ERTS_FD_SET(fd, oset);			
+			    ERTS_FD_SET(fd, oset);
 			}
 			do {
 			    /* Initiate 'tv' each time;
@@ -1939,49 +1489,31 @@ save_poll_result(ErtsPollSet ps, ErtsPollResFd pr[], int max_res,
 			    sres = ERTS_SELECT(ps->max_fd+1, iset, oset, NULL, &tv);
 			} while (sres < 0 && errno == EINTR);
 			if (sres < 0) {
-#if ERTS_POLL_USE_FALLBACK
-			    if (fd == ps->kp_fd) {
-				res += get_kp_results(ps,
-						      &pr[res],
-						      max_res-res);
-				fd++;
-				continue;
-			    }
-#else
 			    if (fd == wake_fd) {
 				cleanup_wakeup_pipe(ps);
 				fd++;
 				continue;
 			    }
-#endif
-			    pr[res].fd = fd;
-			    pr[res].events = ERTS_POLL_EV_NVAL;
+                            ERTS_POLL_RES_SET_FD(&pr[res], fd);
+                            ERTS_POLL_RES_SET_EVTS(&pr[res], ERTS_POLL_EV_NVAL);
 			    res++;
 			}
 			else if (sres > 0) {
-			    pr[res].fd = fd;
+                            ErtsPollEvents events = 0;
+                            ERTS_POLL_RES_SET_FD(&pr[res], fd);
 			    if (iset && ERTS_FD_ISSET(fd, iset)) {
-#if ERTS_POLL_USE_FALLBACK
-				if (fd == ps->kp_fd) {
-				    res += get_kp_results(ps,
-							  &pr[res],
-							  max_res-res);
-				    fd++;
-				    continue;
-				}
-#else
 				if (fd == wake_fd) {
 				    cleanup_wakeup_pipe(ps);
 				    fd++;
 				    continue;
 				}
-#endif
-				pr[res].events |= ERTS_POLL_EV_IN;
+				events |= ERTS_POLL_EV_IN;
 			    }
 			    if (oset && ERTS_FD_ISSET(fd, oset)) {
-				pr[res].events |= ERTS_POLL_EV_OUT;
+				events |= ERTS_POLL_EV_OUT;
 			    }
-			    ASSERT(pr[res].events);
+			    ASSERT(events);
+                            ERTS_POLL_RES_SET_EVTS(&pr[res], events);
 			    res++;
 			}
 		    }
@@ -1996,353 +1528,145 @@ save_poll_result(ErtsPollSet ps, ErtsPollResFd pr[], int max_res,
 	}
 	ps->next_sel_fd = fd;
 	return res;
-#endif
-    }
+#endif /* ERTS_POLL_USE_SELECT */
 }
 
-static ERTS_INLINE ErtsMonotonicTime
-get_timeout(ErtsPollSet ps,
-	    int resolution,
-	    ErtsMonotonicTime timeout_time)
-{
-    ErtsMonotonicTime timeout, save_timeout_time;
-
-    if (timeout_time == ERTS_POLL_NO_TIMEOUT) {
-	save_timeout_time = ERTS_MONOTONIC_TIME_MIN;
-	timeout = 0;
-    }
-    else {
-	ErtsMonotonicTime diff_time, current_time;
-	current_time = erts_get_monotonic_time(NULL);
-	diff_time = timeout_time - current_time;
-	if (diff_time <= 0) {
-	    save_timeout_time = ERTS_MONOTONIC_TIME_MIN;
-	    timeout = 0;
-	}
-	else {
-	    save_timeout_time = current_time;
-	    switch (resolution) {
-	    case 1000:
-		/* Round up to nearest even milli second */
-		timeout = ERTS_MONOTONIC_TO_MSEC(diff_time - 1) + 1;
-		if (timeout > (ErtsMonotonicTime) INT_MAX)
-		    timeout = (ErtsMonotonicTime) INT_MAX;
-		save_timeout_time += ERTS_MSEC_TO_MONOTONIC(timeout);
-		timeout -= ERTS_PREMATURE_TIMEOUT(timeout, 1000);
-		break;
-	    case 1000000:
-		/* Round up to nearest even micro second */
-		timeout = ERTS_MONOTONIC_TO_USEC(diff_time - 1) + 1;
-		save_timeout_time += ERTS_USEC_TO_MONOTONIC(timeout);
-		timeout -= ERTS_PREMATURE_TIMEOUT(timeout, 1000*1000);
-		break;
-	    case 1000000000:
-		/* Round up to nearest even nano second */
-		timeout = ERTS_MONOTONIC_TO_NSEC(diff_time - 1) + 1;
-		save_timeout_time += ERTS_NSEC_TO_MONOTONIC(timeout);
-		timeout -= ERTS_PREMATURE_TIMEOUT(timeout, 1000*1000*1000);
-		break;
-	    default:
-		ERTS_INTERNAL_ERROR("Invalid resolution");
-		timeout = 0;
-		save_timeout_time = 0;
-		break;
-	    }
-	}
-    }
-    set_timeout_time(ps, save_timeout_time);
-    return timeout;
-}
-
-#if ERTS_POLL_USE_SELECT
-
-static ERTS_INLINE int
-get_timeout_timeval(ErtsPollSet ps,
-		    SysTimeval *tvp,
-		    ErtsMonotonicTime timeout_time)
-{
-    ErtsMonotonicTime timeout = get_timeout(ps,
-					    1000*1000,
-					    timeout_time);
-
-    if (!timeout) {
-	tvp->tv_sec = 0;
-	tvp->tv_usec = 0;
-
-	return 0;
-    }
-    else {
-	ErtsMonotonicTime sec = timeout/(1000*1000);
-	tvp->tv_sec = sec;
-	tvp->tv_usec = timeout - sec*(1000*1000);
-
-	ASSERT(tvp->tv_sec >= 0);
-	ASSERT(tvp->tv_usec >= 0);
-	ASSERT(tvp->tv_usec < 1000*1000);
-
-	return !0;
-    }
-
-}
-
-#endif
-
-#if ERTS_POLL_USE_KQUEUE || (ERTS_POLL_USE_POLL && defined(HAVE_PPOLL)) || ERTS_POLL_USE_TIMERFD
-
-static ERTS_INLINE int
-get_timeout_timespec(ErtsPollSet ps,
-		     struct timespec *tsp,
-		     ErtsMonotonicTime timeout_time)
-{
-    ErtsMonotonicTime timeout = get_timeout(ps,
-					    1000*1000*1000,
-					    timeout_time);
-
-    if (!timeout) {
-	tsp->tv_sec = 0;
-	tsp->tv_nsec = 0;
-	return 0;
-    }
-    else {
-	ErtsMonotonicTime sec = timeout/(1000*1000*1000);
-	tsp->tv_sec = sec;
-	tsp->tv_nsec = timeout - sec*(1000*1000*1000);
-
-	ASSERT(tsp->tv_sec >= 0);
-	ASSERT(tsp->tv_nsec >= 0);
-	ASSERT(tsp->tv_nsec < 1000*1000*1000);
-
-	return !0;
-    }
-}
-
-#endif
-
-#if ERTS_POLL_USE_TIMERFD
-
-static ERTS_INLINE int
-get_timeout_itimerspec(ErtsPollSet ps,
-                       struct itimerspec *itsp,
-                       ErtsMonotonicTime timeout_time)
-{
-
-    itsp->it_interval.tv_sec = 0;
-    itsp->it_interval.tv_nsec = 0;
-
-    return get_timeout_timespec(ps, &itsp->it_value, timeout_time);
-}
-
-#endif
+#endif /* !ERTS_POLL_USE_KERNEL_POLL */
 
 static ERTS_INLINE int
-check_fd_events(ErtsPollSet ps, ErtsMonotonicTime timeout_time, int max_res)
+check_fd_events(ErtsPollSet *ps, ErtsPollResFd pr[], int do_wait, int max_res)
 {
     int res;
-    ERTS_MSACC_PUSH_STATE_M();
-    if (erts_atomic_read_nob(&ps->no_of_user_fds) == 0
-	&& timeout_time == ERTS_POLL_NO_TIMEOUT) {
-	/* Nothing to poll and zero timeout; done... */
-	return 0;
-    }
-    else {
-	int timeout;
-#if ERTS_POLL_USE_FALLBACK
-	if (!(ps->fallback_used = ERTS_POLL_NEED_FALLBACK(ps))) {
-
-#if ERTS_POLL_USE_EPOLL		/* --- epoll ------------------------------- */
-	    if (max_res > ps->res_events_len)
-		grow_res_events(ps, max_res);
-#if ERTS_POLL_USE_TIMERFD
-            {
-                struct itimerspec its;
-                timeout = get_timeout_itimerspec(ps, &its, timeout_time);
-                if (timeout) {
-                    erts_thr_progress_prepare_wait(NULL);
-                    ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_SLEEP);
-                    timerfd_set(ps, &its);
-                    res = epoll_wait(ps->kp_fd, ps->res_events, max_res, -1);
-                    res = timerfd_clear(ps, res, max_res);
-                } else {
-                    res = epoll_wait(ps->kp_fd, ps->res_events, max_res, 0);
-                }
-            }
-#else /* !ERTS_POLL_USE_TIMERFD */
-	    timeout = (int) get_timeout(ps, 1000, timeout_time);
-            if (timeout) {
-		erts_thr_progress_prepare_wait(NULL);
-                ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_SLEEP);
-            }
-	    res = epoll_wait(ps->kp_fd, ps->res_events, max_res, timeout);
-#endif /* !ERTS_POLL_USE_TIMERFD */
-#elif ERTS_POLL_USE_KQUEUE	/* --- kqueue ------------------------------ */
-	    struct timespec ts;
-	    if (max_res > ps->res_events_len)
-		grow_res_events(ps, max_res);
-	    timeout = get_timeout_timespec(ps, &ts, timeout_time);
-            if (timeout) {
-		erts_thr_progress_prepare_wait(NULL);
-		ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_SLEEP);
-            }
-	    res = kevent(ps->kp_fd, NULL, 0, ps->res_events, max_res, &ts);
-#endif				/* ----------------------------------------- */
-	}
-	else /* use fallback (i.e. poll() or select()) */
-#endif /* ERTS_POLL_USE_FALLBACK */
-	{
+    int timeout = do_wait ? -1 : 0;
+    DEBUG_PRINT_WAIT("Entering check_fd_events(), do_wait=%d", ps, do_wait);
+    {
+#if ERTS_POLL_USE_EPOLL                /* --- epoll ------------------------------- */
+        res = epoll_wait(ps->kp_fd, pr, max_res, timeout);
+
+#elif ERTS_POLL_USE_KQUEUE     /* --- kqueue ------------------------------ */
+        struct timespec ts = {0, 0};
+        struct timespec *tsp = timeout ? NULL : &ts;
+        res = kevent(ps->kp_fd, NULL, 0, pr, max_res, tsp);
+#elif ERTS_POLL_USE_DEVPOLL	/* --- devpoll ----------------------------- */
+        /*
+         * The ioctl() will fail with EINVAL on Solaris 10 if dp_nfds
+         * is set too high. dp_nfds should not be set greater than
+         * the maximum number of file descriptors in the poll set.
+         */
+        struct dvpoll poll_res;
+        int nfds = (int) erts_atomic_read_nob(&ps->no_of_user_fds) + 1 /* wakeup pipe */;
+        poll_res.dp_nfds = nfds < max_res ? nfds : max_res;
+        poll_res.dp_fds = pr;
+        poll_res.dp_timeout = timeout;
+        res = ioctl(ps->kp_fd, DP_POLL, &poll_res);
 
-#if ERTS_POLL_USE_DEVPOLL	/* --- devpoll ----------------------------- */
-	    /*
-	     * The ioctl() will fail with EINVAL on Solaris 10 if dp_nfds
-	     * is set too high. dp_nfds should not be set greater than
-	     * the maximum number of file descriptors in the poll set.
-	     */
-	    struct dvpoll poll_res;
-	    int nfds = (int) erts_atomic_read_nob(&ps->no_of_user_fds);
-	    nfds++; /* Wakeup pipe */
-	    timeout = (int) get_timeout(ps, 1000, timeout_time);
-	    poll_res.dp_nfds = nfds < max_res ? nfds : max_res;
-	    if (poll_res.dp_nfds > ps->res_events_len)
-		grow_res_events(ps, poll_res.dp_nfds);
-	    poll_res.dp_fds = ps->res_events;
-	    if (timeout) {
-		erts_thr_progress_prepare_wait(NULL);
-                ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_SLEEP);
-            }
-	    poll_res.dp_timeout = timeout;
-	    res = ioctl(ps->kp_fd, DP_POLL, &poll_res);
-#elif ERTS_POLL_USE_POLL && defined(HAVE_PPOLL)	/* --- ppoll ---------------- */
-            struct timespec ts;
-	    timeout = get_timeout_timespec(ps, &ts, timeout_time);
-            if (timeout) {
-		erts_thr_progress_prepare_wait(NULL);
-		ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_SLEEP);
-            }
-            res = ppoll(ps->poll_fds, ps->no_poll_fds, &ts, NULL);
 #elif ERTS_POLL_USE_POLL        /* --- poll --------------------------------- */
-	    timeout = (int) get_timeout(ps, 1000, timeout_time);
 
-	    if (timeout) {
-		erts_thr_progress_prepare_wait(NULL);
-		ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_SLEEP);
-            }
-	    res = poll(ps->poll_fds, ps->no_poll_fds, timeout);
+        res = poll(ps->poll_fds, ps->no_poll_fds, timeout);
+
 #elif ERTS_POLL_USE_SELECT	/* --- select ------------------------------ */
-	    SysTimeval to;
-	    timeout = get_timeout_timeval(ps, &to, timeout_time);
+        SysTimeval tv = {0, 0};
+        SysTimeval *tvp = timeout ? NULL : &tv;
 
-	    ERTS_FD_COPY(&ps->input_fds, &ps->res_input_fds);
-	    ERTS_FD_COPY(&ps->output_fds, &ps->res_output_fds);
+        ERTS_FD_COPY(&ps->input_fds, &ps->res_input_fds);
+        ERTS_FD_COPY(&ps->output_fds, &ps->res_output_fds);
 
-	    if (timeout) {
-		erts_thr_progress_prepare_wait(NULL);
-		ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_SLEEP);
-	    }
-	    res = ERTS_SELECT(ps->max_fd + 1,
-			      &ps->res_input_fds,
-			      &ps->res_output_fds,
-			      NULL,
-			      &to);
-	    if (timeout) {
-		erts_thr_progress_finalize_wait(NULL);
-		ERTS_MSACC_POP_STATE_M();
-	    }
-	    if (res < 0
-		&& errno == EBADF
-		&& ERTS_POLLSET_HAVE_UPDATE_REQUESTS(ps)) {
-		/*
-		 * This may have happened because another thread deselected
-		 * a fd in our poll set and then closed it, i.e. the driver
-		 * behaved correctly. We wan't to avoid looking for a bad
-		 * fd, that may even not exist anymore. Therefore, handle
-		 * update requests and try again.
-		 *
-		 * We don't know how much of the timeout is left; therfore,
-		 * we use a zero timeout. If no error occur and no events
-		 * have triggered, we fake an EAGAIN error and let the caller
-		 * restart us.
-		 */
-		to.tv_sec = 0;
-		to.tv_usec = 0;
-		ERTS_POLLSET_LOCK(ps);
-		handle_update_requests(ps);
-		ERTS_POLLSET_UNLOCK(ps);
-		res = ERTS_SELECT(ps->max_fd + 1,
-				  &ps->res_input_fds,
-				  &ps->res_output_fds,
-				  NULL,
-				  &to);
-		if (res == 0) {
-		    errno = EAGAIN;
-		    res = -1;
-		}
-	    }
-	    return res;
+        res = ERTS_SELECT(ps->max_fd + 1,
+                          &ps->res_input_fds,
+                          &ps->res_output_fds,
+                          NULL,
+                          tvp);
 #endif				/* ----------------------------------------- */
-	}
-	if (timeout) {
-	    erts_thr_progress_finalize_wait(NULL);
-	    ERTS_MSACC_POP_STATE_M();
-	}
-	return res;
     }
+    DEBUG_PRINT_WAIT("Leaving check_fd_events(), res=%d", ps, res);
+    return res;
 }
 
 int
-ERTS_POLL_EXPORT(erts_poll_wait)(ErtsPollSet ps,
+ERTS_POLL_EXPORT(erts_poll_wait)(ErtsPollSet *ps,
 				 ErtsPollResFd pr[],
-				 int *len,
-				 ErtsMonotonicTime timeout_time)
+				 int *len)
 {
-    ErtsMonotonicTime to;
-    int res, no_fds;
+    int res, no_fds, used_fds = 0;
     int ebadf = 0;
+    int do_wait;
     int ps_locked = 0;
+    ERTS_MSACC_DECLARE_CACHE();
 
     no_fds = *len;
-#ifdef ERTS_POLL_MAX_RES
-    if (no_fds >= ERTS_POLL_MAX_RES)
-	no_fds = ERTS_POLL_MAX_RES;
-#endif
-
     *len = 0;
+    ASSERT(no_fds > 0);
 
-#ifdef ERTS_POLL_DEBUG_PRINT
-    erts_printf("Entering erts_poll_wait(), timeout_time=%bps\n",
-		timeout_time);
-#endif
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
+    if (ERTS_POLLSET_HAVE_UPDATE_REQUESTS(ps)) {
+	ERTS_POLLSET_LOCK(ps);
+	used_fds = handle_update_requests(ps, pr, no_fds);
+	ERTS_POLLSET_UNLOCK(ps);
 
-    if (ERTS_POLLSET_SET_POLLED_CHK(ps)) {
-	res = EINVAL; /* Another thread is in erts_poll_wait()
-			 on this pollset... */
-	goto done;
+        if (used_fds == no_fds) {
+            *len = used_fds;
+            return 0;
+        }
     }
+#endif
 
-    to = (is_woken(ps)
-	  ? ERTS_POLL_NO_TIMEOUT /* Use zero timeout */
-	  : timeout_time);
+    do_wait = !is_woken(ps) && used_fds == 0;
 
-    if (ERTS_POLLSET_HAVE_UPDATE_REQUESTS(ps)) {
-	ERTS_POLLSET_LOCK(ps);
-	handle_update_requests(ps);
-	ERTS_POLLSET_UNLOCK(ps);
+    DEBUG_PRINT_WAIT("Entering %s(), do_wait=%d", ps, __FUNCTION__, do_wait);
+
+    if (do_wait) {
+        erts_thr_progress_prepare_wait(NULL);
+        ERTS_MSACC_SET_STATE_CACHED(ERTS_MSACC_STATE_SLEEP);
     }
 
     while (1) {
-	res = check_fd_events(ps, to, no_fds);
+	res = check_fd_events(ps, pr + used_fds, do_wait, no_fds - used_fds);
+
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
+        if (res < 0
+            && errno == EBADF
+            && ERTS_POLLSET_HAVE_UPDATE_REQUESTS(ps)) {
+            /*
+             * This may have happened because another thread deselected
+             * a fd in our poll set and then closed it, i.e. the driver
+             * behaved correctly. We wan't to avoid looking for a bad
+             * fd, that may even not exist anymore. Therefore, handle
+             * update requests and try again. This behaviour should only
+             * happen when using SELECT as the polling mechanism.
+             */
+            ERTS_POLLSET_LOCK(ps);
+            used_fds += handle_update_requests(ps, pr + used_fds, no_fds - used_fds);
+            if (used_fds == no_fds) {
+                *len = used_fds;
+                ERTS_POLLSET_UNLOCK(ps);
+                return 0;
+            }
+            res = check_fd_events(ps, pr + used_fds, 0, no_fds - used_fds);
+            /* Keep the lock over the non-blocking poll in order to not
+               get any nasty races happening. */
+            ERTS_POLLSET_UNLOCK(ps);
+            if (res == 0) {
+                errno = EAGAIN;
+                res = -1;
+            }
+        }
+#endif
+
 	if (res != 0)
 	    break;
-	if (to == ERTS_POLL_NO_TIMEOUT)
-	    break;
-	if (erts_get_monotonic_time(NULL) >= timeout_time)
-	    break;
+        if (!do_wait)
+            break;
+    }
+
+    if (do_wait) {
+        erts_thr_progress_finalize_wait(NULL);
+        ERTS_MSACC_UPDATE_CACHE();
+        ERTS_MSACC_SET_STATE_CACHED(ERTS_MSACC_STATE_CHECK_IO);
     }
 
     woke_up(ps);
 
-    if (res == 0) {
-	res = ETIMEDOUT;
-    }
-    else if (res < 0) {
+    if (res < 0) {
 #if ERTS_POLL_USE_SELECT
 	if (errno == EBADF) {
 	    ebadf = 1;
@@ -2359,26 +1683,21 @@ ERTS_POLL_EXPORT(erts_poll_wait)(ErtsPollSet ps,
 	ps_locked = 1;
 	ERTS_POLLSET_LOCK(ps);
 
-	no_fds = save_poll_result(ps, pr, no_fds, res, ebadf);
+	used_fds += ERTS_POLL_EXPORT(save_result)(ps, pr + used_fds, no_fds - used_fds, res, ebadf);
 
 #ifdef HARD_DEBUG
-	check_poll_result(pr, no_fds);
+	check_poll_result(pr, used_fds);
 #endif
 
-	res = (no_fds == 0 ? (is_interrupted_reset(ps) ? EINTR : EAGAIN) : 0);
-	*len = no_fds;
+	res = (used_fds == 0 ? (is_interrupted_reset(ps) ? EINTR : EAGAIN) : 0);
+	*len = used_fds;
     }
 
     if (ps_locked)
 	ERTS_POLLSET_UNLOCK(ps);
-    ERTS_POLLSET_UNSET_POLLED(ps);
 
- done:
-    set_timeout_time(ps, ERTS_MONOTONIC_TIME_MAX);
-#ifdef ERTS_POLL_DEBUG_PRINT
-    erts_printf("Leaving %s = erts_poll_wait()\n",
-		 res == 0 ? "0" : erl_errno_id(res));
-#endif
+    DEBUG_PRINT_WAIT("Leaving %s = %s(len = %d)", ps,
+                     res == 0 ? "0" : erl_errno_id(res), __FUNCTION__, *len);
 
     return res;
 }
@@ -2388,40 +1707,14 @@ ERTS_POLL_EXPORT(erts_poll_wait)(ErtsPollSet ps,
  */
 
 void
-ERTS_POLL_EXPORT(erts_poll_interrupt)(ErtsPollSet ps, int set)
+ERTS_POLL_EXPORT(erts_poll_interrupt)(ErtsPollSet *ps, int set)
 {
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
     if (!set)
 	reset_wakeup_state(ps);
     else
-	wake_poller(ps, 1, 0);
-}
-
-
-/*
- * erts_poll_interrupt_timed():
- *   If 'set' != 0, interrupt thread blocked in erts_poll_wait() if it
- * is not guaranteed that it will timeout before 'msec' milli seconds.
- */
-void
-ERTS_POLL_EXPORT(erts_poll_interrupt_timed)(ErtsPollSet ps,
-					    int set,
-					    ErtsMonotonicTime timeout_time)
-{
-    if (!set)
-	reset_wakeup_state(ps);
-    else {
-	ErtsMonotonicTime max_wait_time = get_timeout_time(ps);
-	if (max_wait_time > timeout_time)
-	    wake_poller(ps, 1, 0);
-#ifdef ERTS_POLL_COUNT_AVOIDED_WAKEUPS
-	else {
-	    if (ERTS_POLLSET_IS_POLLED(ps))
-		erts_atomic_inc_nob(&ps->no_avoided_wakeups);
-	    erts_atomic_inc_nob(&ps->no_avoided_interrupts);
-	}
-	erts_atomic_inc_nob(&ps->no_interrupt_timed);
+	wake_poller(ps, 1);
 #endif
-    }
 }
 
 int
@@ -2434,14 +1727,19 @@ ERTS_POLL_EXPORT(erts_poll_max_fds)(void)
  */
 
 void
-ERTS_POLL_EXPORT(erts_poll_init)(void)
+ERTS_POLL_EXPORT(erts_poll_init)(int *concurrent_updates)
 {
-    erts_mtx_init(&pollsets_lock, "pollsets_lock", NIL,
-        ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_IO);
-    pollsets = NULL;
 
     errno = 0;
 
+    if (concurrent_updates) {
+#if ERTS_POLL_USE_CONCURRENT_UPDATE
+        *concurrent_updates = 1;
+#else
+        *concurrent_updates = 0;
+#endif
+    }
+
 #if !defined(NO_SYSCONF)
     max_fds = sysconf(_SC_OPEN_MAX);
 #elif ERTS_POLL_USE_SELECT
@@ -2460,37 +1758,28 @@ ERTS_POLL_EXPORT(erts_poll_init)(void)
 	fatal_error("erts_poll_init(): Failed to get max number of files: %s\n",
 		    erl_errno_id(errno));
 
-#ifdef ERTS_POLL_DEBUG_PRINT
     print_misc_debug_info();
-#endif
 }
 
-ErtsPollSet
-ERTS_POLL_EXPORT(erts_poll_create_pollset)(void)
+ErtsPollSet *
+ERTS_POLL_EXPORT(erts_poll_create_pollset)(int id)
 {
 #if ERTS_POLL_USE_KERNEL_POLL
     int kp_fd;
 #endif
-    ErtsPollSet ps = erts_alloc(ERTS_ALC_T_POLLSET,
-				sizeof(struct ErtsPollSet_));
+    ErtsPollSet *ps = erts_alloc(ERTS_ALC_T_POLLSET,
+				sizeof(struct ERTS_POLL_EXPORT(erts_pollset)));
+    ps->id = id;
     ps->internal_fd_limit = 0;
-    ps->fds_status = NULL;
-    ps->fds_status_len = 0;
     erts_atomic_init_nob(&ps->no_of_user_fds, 0);
 #if ERTS_POLL_USE_KERNEL_POLL
     ps->kp_fd = -1;
 #if ERTS_POLL_USE_EPOLL
     kp_fd = epoll_create(256);
-    ps->res_events_len = 0;
-    ps->res_events = NULL;
 #elif ERTS_POLL_USE_DEVPOLL
     kp_fd = open("/dev/poll", O_RDWR);
-    ps->res_events_len = 0;
-    ps->res_events = NULL;
 #elif ERTS_POLL_USE_KQUEUE
     kp_fd = kqueue();
-    ps->res_events_len = 0;
-    ps->res_events = NULL;
 #endif
     if (kp_fd < 0)
 	fatal_error("erts_poll_create_pollset(): Failed to "
@@ -2504,10 +1793,6 @@ ERTS_POLL_EXPORT(erts_poll_create_pollset)(void)
 		    ": %s (%d)\n",
 		    erl_errno_id(errno), errno);
 #endif /* ERTS_POLL_USE_KERNEL_POLL */
-#if ERTS_POLL_USE_BATCH_UPDATE_POLLSET
-    /* res_events is also used as write buffer */
-    grow_res_events(ps, ERTS_POLL_MIN_BATCH_BUF_SIZE);
-#endif
 #if ERTS_POLL_USE_POLL
     ps->next_poll_fds_ix = 0;
     ps->no_poll_fds = 0;
@@ -2516,9 +1801,6 @@ ERTS_POLL_EXPORT(erts_poll_create_pollset)(void)
 #elif ERTS_POLL_USE_SELECT
     ps->next_sel_fd = 0;
     ps->max_fd = -1;
-#if ERTS_POLL_USE_FALLBACK
-    ps->no_select_fds = 0;
-#endif
 #ifdef _DARWIN_UNLIMITED_SELECT
     ps->input_fds.sz = 0;
     ps->input_fds.ptr = NULL;
@@ -2535,140 +1817,85 @@ ERTS_POLL_EXPORT(erts_poll_create_pollset)(void)
     ERTS_FD_ZERO(&ps->res_output_fds);
 #endif
 #endif
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
+    ps->fds_status = NULL;
+    ps->fds_status_len = 0;
     ps->update_requests.next = NULL;
     ps->update_requests.len = 0;
     ps->curr_upd_req_block = &ps->update_requests;
     erts_atomic32_init_nob(&ps->have_update_requests, 0);
-    erts_atomic32_init_nob(&ps->polled, 0);
     erts_mtx_init(&ps->mtx, "pollset", NIL, ERTS_LOCK_FLAGS_CATEGORY_IO);
-    erts_atomic32_init_nob(&ps->wakeup_state, (erts_aint32_t) 0);
-    create_wakeup_pipe(ps);
-#if ERTS_POLL_USE_TIMERFD
-    create_timerfd(ps);
-#endif
-#if ERTS_POLL_USE_FALLBACK
-    if (kp_fd >= ps->fds_status_len)
-	grow_fds_status(ps, kp_fd);
-    /* Force kernel poll fd into fallback (poll/select) set */
-    ps->fds_status[kp_fd].flags
-	|= ERTS_POLL_FD_FLG_INFLBCK|ERTS_POLL_FD_FLG_USEFLBCK;
-    {
-	int do_wake = 0;
-	ERTS_POLL_EXPORT(erts_poll_control)(ps, kp_fd, ERTS_POLL_EV_IN, 1,
-					    &do_wake);
-    }    
 #endif
 #if ERTS_POLL_USE_KERNEL_POLL
     if (ps->internal_fd_limit <= kp_fd)
 	ps->internal_fd_limit = kp_fd + 1;
     ps->kp_fd = kp_fd;
 #endif
-    init_timeout_time(ps);
-#ifdef ERTS_POLL_COUNT_AVOIDED_WAKEUPS
-    erts_atomic_init_nob(&ps->no_avoided_wakeups, 0);
-    erts_atomic_init_nob(&ps->no_avoided_interrupts, 0);
-    erts_atomic_init_nob(&ps->no_interrupt_timed, 0);
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
+    erts_atomic32_init_nob(&ps->wakeup_state, (erts_aint32_t) 0);
+    create_wakeup_pipe(ps);
+    handle_update_requests(ps, NULL, 0);
+    cleanup_wakeup_pipe(ps);
 #endif
-    handle_update_requests(ps);
-#if ERTS_POLL_USE_FALLBACK
-    ps->fallback_used = 0;
+#if ERTS_POLL_USE_KERNEL_POLL && (defined(__DARWIN__) || defined(__APPLE__) && defined(__MACH__))
+    {
+        /*
+         * Using kqueue on OS X is a mess of brokenness...
+         *
+         * On OS X version older than 15.6 (i.e. OS X El Capitan released in July 2015),
+         * a thread waiting in kevent is not woken if an event is inserted into the kqueue
+         * by another thread and the event becomes ready. However if a new call to kevent
+         * is done by the waiting thread, the new event is found.
+         *
+         * So on effected OS X versions we could trigger the wakeup pipe so that
+         * the waiters will be woken and re-issue the kevent. However...
+         *
+         * On OS X version older then 16 (i.e. OS X Sierra released in September 2016),
+         * running the emulator driver_SUITE smp_select testcase consistently causes a
+         * kernel panic. I don't know why or what events that trigger it. But it seems
+         * like updates of the pollset while another thread is sleeping in it Creates
+         * some kind of race that triggers the kernel panic.
+         *
+         * So to deal with this, the erts configure check what OS X version is run
+         * and only enabled kernel poll on OS X 16 or newer. In addition, if someone
+         * attempts to compile Erlang on OS X 16 and then run it on OS X 15, we do the
+         * run-time check below to disallow this.
+         */
+        int major, minor, build;
+        os_version(&major,&minor,&build);
+        if (major < 16) {
+            erts_fprintf(stderr,"BROKEN KQUEUE!\n"
+                         "Erlang has been compiled with kernel-poll support,\n"
+                         "but this OS X version is known to have kernel bugs\n"
+                         "when using kernel-poll. You have two options:\n"
+                         " 1) update to a newer OS X version (OS X Sierra or newer)\n"
+                         " 2) recompile erlang without kernel-poll support\n");
+            erts_exit(1, "");
+        }
+    }
 #endif
     erts_atomic_set_nob(&ps->no_of_user_fds, 0); /* Don't count wakeup pipe and fallback fd */
 
-    erts_mtx_lock(&pollsets_lock);
-    ps->next = pollsets;
-    pollsets = ps;
-    erts_mtx_unlock(&pollsets_lock);
-
     return ps;
 }
 
-void
-ERTS_POLL_EXPORT(erts_poll_destroy_pollset)(ErtsPollSet ps)
-{
-
-    if (ps->fds_status)
-	erts_free(ERTS_ALC_T_FD_STATUS, (void *) ps->fds_status);
-
-#if ERTS_POLL_USE_EPOLL
-    if (ps->kp_fd >= 0)
-	close(ps->kp_fd);
-    if (ps->res_events)
-	erts_free(ERTS_ALC_T_POLL_RES_EVS, (void *) ps->res_events);
-#elif ERTS_POLL_USE_DEVPOLL
-    if (ps->kp_fd >= 0)
-	close(ps->kp_fd);
-    if (ps->res_events)
-	erts_free(ERTS_ALC_T_POLL_RES_EVS, (void *) ps->res_events);
-#elif ERTS_POLL_USE_POLL
-    if (ps->poll_fds)
-	erts_free(ERTS_ALC_T_POLL_FDS, (void *) ps->poll_fds);
-#elif ERTS_POLL_USE_SELECT
-#ifdef _DARWIN_UNLIMITED_SELECT
-    if (ps->input_fds.ptr)
-	erts_free(ERTS_ALC_T_SELECT_FDS, (void *) ps->input_fds.ptr);
-    if (ps->res_input_fds.ptr)
-	erts_free(ERTS_ALC_T_SELECT_FDS, (void *) ps->res_input_fds.ptr);
-    if (ps->output_fds.ptr)
-	erts_free(ERTS_ALC_T_SELECT_FDS, (void *) ps->output_fds.ptr);
-    if (ps->res_output_fds.ptr)
-	erts_free(ERTS_ALC_T_SELECT_FDS, (void *) ps->res_output_fds.ptr);
-#endif
-#endif
-    {
-	ErtsPollSetUpdateRequestsBlock *urqbp = ps->update_requests.next;
-	while (urqbp) {
-	    ErtsPollSetUpdateRequestsBlock *free_urqbp = urqbp;
-	    urqbp = urqbp->next;
-	    free_update_requests_block(ps, free_urqbp);
-	}
-    }
-    erts_mtx_destroy(&ps->mtx);
-    if (ps->wake_fds[0] >= 0)
-	close(ps->wake_fds[0]);
-    if (ps->wake_fds[1] >= 0)
-	close(ps->wake_fds[1]);
-#if ERTS_POLL_USE_TIMERFD
-    if (ps->timer_fd >= 0)
-        close(ps->timer_fd);
-#endif
-
-    erts_mtx_lock(&pollsets_lock);
-    if (ps == pollsets)
-	pollsets = pollsets->next;
-    else {
-	ErtsPollSet prev_ps;
-	for (prev_ps = pollsets; ps != prev_ps->next; prev_ps = prev_ps->next)
-            ;
-	ASSERT(ps == prev_ps->next);
-	prev_ps->next = ps->next;
-    }
-    erts_mtx_unlock(&pollsets_lock);
-
-    erts_free(ERTS_ALC_T_POLLSET, (void *) ps);
-}
-
 /*
  * --- Info ------------------------------------------------------------------
  */
 
 void
-ERTS_POLL_EXPORT(erts_poll_info)(ErtsPollSet ps, ErtsPollInfo *pip)
+ERTS_POLL_EXPORT(erts_poll_info)(ErtsPollSet *ps, ErtsPollInfo *pip)
 {
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
     int pending_updates;
+#endif
     Uint size = 0;
 
     ERTS_POLLSET_LOCK(ps);
 
-    size += sizeof(struct ErtsPollSet_);
+    size += sizeof(struct ERTS_POLL_EXPORT(erts_pollset));
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
     size += ps->fds_status_len*sizeof(ErtsFdStatus);
-
-#if ERTS_POLL_USE_EPOLL
-    size += ps->res_events_len*sizeof(struct epoll_event);
-#elif ERTS_POLL_USE_DEVPOLL
-    size += ps->res_events_len*sizeof(struct pollfd);
-#elif ERTS_POLL_USE_KQUEUE
-    size += ps->res_events_len*sizeof(struct kevent);
 #endif
 
 #if ERTS_POLL_USE_POLL
@@ -2680,6 +1907,7 @@ ERTS_POLL_EXPORT(erts_poll_info)(ErtsPollSet ps, ErtsPollInfo *pip)
 #endif
 #endif
 
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
     {
 	ErtsPollSetUpdateRequestsBlock *urqbp = ps->update_requests.next;
 	pending_updates = ps->update_requests.len;
@@ -2689,8 +1917,9 @@ ERTS_POLL_EXPORT(erts_poll_info)(ErtsPollSet ps, ErtsPollInfo *pip)
 	    urqbp = urqbp->next;
 	}
     }
+#endif
 
-    pip->primary = 
+    pip->primary =
 #if ERTS_POLL_USE_KQUEUE
 	"kqueue"
 #elif ERTS_POLL_USE_EPOLL
@@ -2704,17 +1933,7 @@ ERTS_POLL_EXPORT(erts_poll_info)(ErtsPollSet ps, ErtsPollInfo *pip)
 #endif
 	;
 
-    pip->fallback = 
-#if !ERTS_POLL_USE_FALLBACK
-	NULL
-#elif ERTS_POLL_USE_POLL
-	"poll"
-#elif ERTS_POLL_USE_SELECT
-	"select"
-#endif
-	;
-
-    pip->kernel_poll = 
+    pip->kernel_poll =
 #if !ERTS_POLL_USE_KERNEL_POLL
 	NULL
 #elif ERTS_POLL_USE_KQUEUE
@@ -2729,40 +1948,21 @@ ERTS_POLL_EXPORT(erts_poll_info)(ErtsPollSet ps, ErtsPollInfo *pip)
     pip->memory_size = size;
 
     pip->poll_set_size = (int) erts_atomic_read_nob(&ps->no_of_user_fds);
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
     pip->poll_set_size++; /* Wakeup pipe */
-#if ERTS_POLL_USE_TIMERFD
-    pip->poll_set_size++; /* timerfd */
-#endif
-
-    pip->fallback_poll_set_size =
-#if !ERTS_POLL_USE_FALLBACK
-	0
-#elif ERTS_POLL_USE_POLL
-	ps->no_poll_fds
-#elif ERTS_POLL_USE_SELECT
-	ps->no_select_fds
-#endif
-	;
-
-#if ERTS_POLL_USE_FALLBACK
-    /* If only kp_fd is in fallback poll set we don't use fallback... */
-    if (pip->fallback_poll_set_size == 1)
-	pip->fallback_poll_set_size = 0;
-    else
-	pip->poll_set_size++; /* kp_fd */
 #endif
 
     pip->lazy_updates =
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
 	1
+#else
+	0
+#endif
 	;
 
     pip->pending_updates = 
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
 	pending_updates
-	;
-
-    pip->batch_updates = 
-#if ERTS_POLL_USE_BATCH_UPDATE_POLLSET
-	1
 #else
 	0
 #endif
@@ -2776,13 +1976,23 @@ ERTS_POLL_EXPORT(erts_poll_info)(ErtsPollSet ps, ErtsPollInfo *pip)
 #endif
 	;
 
-    pip->max_fds = max_fds;
+    pip->is_fallback =
+#if ERTS_POLL_IS_FALLBACK
+        1
+#else
+        0
+#endif
+        ;
 
-#ifdef ERTS_POLL_COUNT_AVOIDED_WAKEUPS
-    pip->no_avoided_wakeups = erts_atomic_read_nob(&ps->no_avoided_wakeups);
-    pip->no_avoided_interrupts = erts_atomic_read_nob(&ps->no_avoided_interrupts);
-    pip->no_interrupt_timed = erts_atomic_read_nob(&ps->no_interrupt_timed);
+    pip->batch_updates =
+#if ERTS_POLL_USE_DEVPOLL
+        1
+#else
+        0
 #endif
+        ;
+
+    pip->max_fds = max_fds;
 
     ERTS_POLLSET_UNLOCK(ps);
 
@@ -2818,35 +2028,60 @@ fatal_error(char *format, ...)
     abort();
 }
 
-static void
-fatal_error_async_signal_safe(char *error_str)
+/*
+ * --- Debug -----------------------------------------------------------------
+ */
+
+#if ERTS_POLL_USE_EPOLL
+uint32_t epoll_events(int kp_fd, int fd)
 {
-    if (ERTS_SOMEONE_IS_CRASH_DUMPING || ERTS_GOT_SIGUSR1) {
-	/* See comment above in fatal_error() */
-	return;
+    /* For epoll we read the information about what is selected upon from the proc fs.*/
+    char fname[30];
+    FILE *f;
+    unsigned int pos, flags, mnt_id;
+    int line = 0;
+    sprintf(fname,"/proc/%d/fdinfo/%d",getpid(), kp_fd);
+    f = fopen(fname,"r");
+    if (!f) {
+        fprintf(stderr,"failed to open file %s, errno = %d\n", fname, errno);
+        ASSERT(0);
+        return 0;
     }
-    if (error_str) {
-	int len = 0;
-	while (error_str[len])
-	    len++;
-	if (len) {
-	    /* async signal safe */
-	    erts_silence_warn_unused_result(write(2, error_str, len));
-	}
+    if (fscanf(f,"pos:\t%x\nflags:\t%x", &pos, &flags) != 2) {
+        fprintf(stderr,"failed to parse file %s, errno = %d\n", fname, errno);
+        ASSERT(0);
+        return 0;
     }
-    abort();
+    if (fscanf(f,"\nmnt_id:\t%x\n", &mnt_id));
+    line += 3;
+    while (!feof(f)) {
+        /* tfd:       10 events: 40000019 data:       180000000a */
+        int ev_fd;
+        uint32_t events;
+        uint64_t data;
+        if (fscanf(f,"tfd:%d events:%x data:%lx\n", &ev_fd, &events, &data) != 3) {
+            fprintf(stderr,"failed to parse file %s on line %d, errno = %d\n", fname,
+                    line,
+                    errno);
+            return 0;
+        }
+        if (fd == ev_fd) {
+            fclose(f);
+            return events;
+        }
+    }
+    fclose(f);
+    return 0;
 }
- 
-/*
- * --- Debug -----------------------------------------------------------------
- */
+#endif
 
 void
-ERTS_POLL_EXPORT(erts_poll_get_selected_events)(ErtsPollSet ps,
+ERTS_POLL_EXPORT(erts_poll_get_selected_events)(ErtsPollSet *ps,
 						ErtsPollEvents ev[],
 						int len)
 {
     int fd;
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
     ERTS_POLLSET_LOCK(ps);
     for (fd = 0; fd < len; fd++) {
 	if (fd >= ps->fds_status_len)
@@ -2855,9 +2090,6 @@ ERTS_POLL_EXPORT(erts_poll_get_selected_events)(ErtsPollSet ps,
 	    ev[fd] = ps->fds_status[fd].events;
             if (
                 fd == ps->wake_fds[0] || fd == ps->wake_fds[1] ||
-#if ERTS_POLL_USE_TIMERFD
-                fd == ps->timer_fd ||
-#endif
 #if ERTS_POLL_USE_KERNEL_POLL
                 fd == ps->kp_fd ||
 #endif
@@ -2866,7 +2098,50 @@ ERTS_POLL_EXPORT(erts_poll_get_selected_events)(ErtsPollSet ps,
 	}
     }
     ERTS_POLLSET_UNLOCK(ps);
+#elif ERTS_POLL_USE_EPOLL
 
+    /* For epoll we read the information about what is selected upon from the proc fs.*/
+    char fname[30];
+    FILE *f;
+    unsigned int pos, flags, mnt_id;
+    int line = 0;
+    sprintf(fname,"/proc/%d/fdinfo/%d",getpid(), ps->kp_fd);
+    for (fd = 0; fd < len; fd++)
+        ev[fd] = ERTS_POLL_EV_NONE;
+    f = fopen(fname,"r");
+    if (!f) {
+        fprintf(stderr,"failed to open file %s, errno = %d\n", fname, errno);
+        return;
+    }
+    if (fscanf(f,"pos:\t%x\nflags:\t%x", &pos, &flags) != 2) {
+        fprintf(stderr,"failed to parse file %s, errno = %d\n", fname, errno);
+        ASSERT(0);
+        return;
+    }
+    if (fscanf(f,"\nmnt_id:\t%x\n", &mnt_id));
+    line += 3;
+    while (!feof(f)) {
+        /* tfd:       10 events: 40000019 data:       180000000a */
+        int fd;
+        uint32_t events;
+        uint64_t data;
+        if (fscanf(f,"tfd:%d events:%x data:%lx\n", &fd, &events, &data) != 3) {
+            fprintf(stderr,"failed to parse file %s on line %d, errno = %d\n",
+                    fname, line, errno);
+            ASSERT(0);
+            return;
+        }
+        data &= 0xFFFFFFFF;
+        ASSERT(fd == data);
+        /* Events are the events that are being monitored, which of course include
+           error and hup events, but we are only interested in IN/OUT events */
+        ev[fd] = (ERTS_POLL_EV_IN|ERTS_POLL_EV_OUT) & ERTS_POLL_EV_N2E(events);
+        line++;
+    }
+#else
+    for (fd = 0; fd < len; fd++)
+        ev[fd] = ERTS_POLL_EV_NONE;
+#endif
 }
 
 #ifdef HARD_DEBUG
@@ -2886,10 +2161,10 @@ check_poll_result(ErtsPollResFd pr[], int len)
 }
 
 
-#if ERTS_POLL_USE_DEVPOLL
+#if ERTS_POLL_USE_DEVPOLL && defined(DEBUG)
 
 static void
-check_poll_status(ErtsPollSet ps)
+check_poll_status(ErtsPollSet *ps)
 {
     int i;
     for (i = 0; i < ps->fds_status_len; i++) {
@@ -2921,30 +2196,24 @@ check_poll_status(ErtsPollSet ps)
 #endif /* ERTS_POLL_USE_DEVPOLL */
 #endif /* HARD_DEBUG */
 
-#ifdef ERTS_POLL_DEBUG_PRINT
 static void
 print_misc_debug_info(void)
 {
-    erts_printf("erts_poll using: %s lazy_updates:%s batch_updates:%s\n",
+#if ERTS_POLL_DEBUG_PRINT
+    erts_printf("erts_poll using: %s lazy_updates:%s\n",
 #if ERTS_POLL_USE_KQUEUE
 		"kqueue"
 #elif ERTS_POLL_USE_EPOLL
 		"epoll"
 #elif ERTS_POLL_USE_DEVPOLL
 		"/dev/poll"
-#endif
-#if ERTS_POLL_USE_FALLBACK
-		"-"
-#endif
-#if ERTS_POLL_USE_POLL
+#elif ERTS_POLL_USE_POLL
 		"poll"
 #elif ERTS_POLL_USE_SELECT
 		"select"
 #endif
 		,
-		"true"
-		,
-#if ERTS_POLL_USE_BATCH_UPDATE_POLLSET
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
 		"true"
 #else
 		"false"
@@ -2963,29 +2232,20 @@ print_misc_debug_info(void)
 #ifdef FD_SETSIZE
     erts_printf("FD_SETSIZE=%d\n", FD_SETSIZE);
 #endif
-}
-    
 #endif
+}
 
 #ifdef ERTS_ENABLE_LOCK_COUNT
-static void erts_lcnt_enable_pollset_lock_count(ErtsPollSet pollset, int enable) {
+void ERTS_POLL_EXPORT(erts_lcnt_enable_pollset_lock_count)(ErtsPollSet *pollset, int enable)
+{
+#if !ERTS_POLL_USE_CONCURRENT_UPDATE
     if(enable) {
         erts_lcnt_install_new_lock_info(&pollset->mtx.lcnt, "pollset_rm", NIL,
             ERTS_LOCK_TYPE_MUTEX | ERTS_LOCK_FLAGS_CATEGORY_IO);
     } else {
         erts_lcnt_uninstall(&pollset->mtx.lcnt);
     }
-}
-
-void ERTS_POLL_EXPORT(erts_lcnt_update_pollset_locks)(int enable) {
-    ErtsPollSet iterator;
-
-    erts_mtx_lock(&pollsets_lock);
-
-    for(iterator = pollsets; iterator != NULL; iterator = iterator->next) {
-        erts_lcnt_enable_pollset_lock_count(iterator, enable);
-    }
-
-    erts_mtx_unlock(&pollsets_lock);
+#endif
+    return;
 }
 #endif
diff --git a/erts/emulator/sys/common/erl_poll.h b/erts/emulator/sys/common/erl_poll.h
index a57dc51e5b..e9a667cac1 100644
--- a/erts/emulator/sys/common/erl_poll.h
+++ b/erts/emulator/sys/common/erl_poll.h
@@ -18,11 +18,31 @@
  * %CopyrightEnd%
  */
 
-/*
- * Description:	Poll interface suitable for ERTS with or without
- *              SMP support.
+/**
+ * @description: Poll interface suitable for ERTS with SMP support.
+ *
+ * @author: 	Rickard Green
+ * @author: 	Lukas Larsson
+ *
+ * This header file exports macros and functions that are used to
+ * react to I/O polling events from file descriptors or wait-able
+ * objects. The API exported is the following:
  *
- * Author: 	Rickard Green
+ * defines:
+ *   ERTS_POLL_EV_NONE - No events have been set. This is not the same as 0.
+ *   ERTS_POLL_EV_IN   - Represent an IN event
+ *   ERTS_POLL_EV_OUT  - Represent an OUT event
+ *   ERTS_POLL_EV_ERR  - Represent an error event
+ *   ERTS_POLL_EV_NVAL - Represent an invalid event
+ *
+ * macro functions:
+ *   ErtsSysFdType ERTS_POLL_RES_GET_FD(ErtsPollResFd *evt);
+ *   void ERTS_POLL_RES_SET_FD(ErtsPollResFd *evt, ErtsSysFdType fd);
+ *   ErtsPollEvents ERTS_POLL_RES_GET_EVTS(ErtsPollResFd *evt)
+ *   void ERTS_POLL_RES_SET_EVTS(ErtsPollResFd *evt, ErtsPollEvents fd);
+ *
+ * functions:
+ *   See erl_poll_api.h
  */
 
 #ifndef ERL_POLL_H__
@@ -32,33 +52,27 @@
 
 #define ERTS_POLL_NO_TIMEOUT ERTS_MONOTONIC_TIME_MIN
 
-#if 0
-#define ERTS_POLL_COUNT_AVOIDED_WAKEUPS
-#endif
-
 #ifdef ERTS_ENABLE_KERNEL_POLL
-#  if defined(ERTS_KERNEL_POLL_VERSION)
-#    define ERTS_POLL_EXPORT(FUNC) FUNC ## _kp
+#  undef ERTS_ENABLE_KERNEL_POLL
+#  define ERTS_ENABLE_KERNEL_POLL 1
+#  if defined(ERTS_NO_KERNEL_POLL_VERSION)
+#    define ERTS_POLL_EXPORT(FUNC) FUNC ## _flbk
+#    undef ERTS_NO_KERNEL_POLL_VERSION
+#    define ERTS_NO_KERNEL_POLL_VERSION 1
+#    define ERTS_KERNEL_POLL_VERSION 0
 #  else
-#    define ERTS_POLL_EXPORT(FUNC) FUNC ## _nkp
-#    undef ERTS_POLL_DISABLE_KERNEL_POLL
-#    define ERTS_POLL_DISABLE_KERNEL_POLL
+#    undef ERTS_KERNEL_POLL_VERSION
+#    define ERTS_KERNEL_POLL_VERSION 1
+#    define ERTS_NO_KERNEL_POLL_VERSION 0
+#    define ERTS_POLL_EXPORT(FUNC) FUNC
 #  endif
 #else
 #    define ERTS_POLL_EXPORT(FUNC) FUNC
-#    undef ERTS_POLL_DISABLE_KERNEL_POLL
-#    define ERTS_POLL_DISABLE_KERNEL_POLL
-#endif
-
-#ifdef ERTS_POLL_DISABLE_KERNEL_POLL
-#  undef HAVE_SYS_EPOLL_H
-#  undef HAVE_SYS_EVENT_H
-#  undef HAVE_SYS_DEVPOLL_H
+#    define ERTS_ENABLE_KERNEL_POLL 0
+#    define ERTS_NO_KERNEL_POLL_VERSION 1
+#    define ERTS_KERNEL_POLL_VERSION 0
 #endif
 
-#undef ERTS_POLL_USE_KERNEL_POLL
-#define ERTS_POLL_USE_KERNEL_POLL 0
-
 #undef ERTS_POLL_USE_KQUEUE
 #define ERTS_POLL_USE_KQUEUE 0
 #undef ERTS_POLL_USE_EPOLL
@@ -70,68 +84,96 @@
 #undef ERTS_POLL_USE_SELECT
 #define ERTS_POLL_USE_SELECT 0
 
-#if defined(HAVE_SYS_EVENT_H)
-#  undef ERTS_POLL_USE_KQUEUE
-#  define ERTS_POLL_USE_KQUEUE 1
-#  undef ERTS_POLL_USE_KERNEL_POLL
-#  define ERTS_POLL_USE_KERNEL_POLL 1
-#elif defined(HAVE_SYS_EPOLL_H)
-#  undef ERTS_POLL_USE_EPOLL
-#  define ERTS_POLL_USE_EPOLL 1
-#  undef ERTS_POLL_USE_KERNEL_POLL
-#  define ERTS_POLL_USE_KERNEL_POLL 1
-#elif defined(HAVE_SYS_DEVPOLL_H)
-#  undef ERTS_POLL_USE_DEVPOLL
-#  define ERTS_POLL_USE_DEVPOLL 1
-#  undef ERTS_POLL_USE_KERNEL_POLL
-#  define ERTS_POLL_USE_KERNEL_POLL 1
+/* Defines which structure that erts_poll_wait should use to wait with
+   and how events should be represented */
+#define ERTS_POLL_USE_EPOLL_EVS 0
+#define ERTS_POLL_USE_KQUEUE_EVS 0
+#define ERTS_POLL_USE_DEVPOLL_EVS 0
+#define ERTS_POLL_USE_POLL_EVS 0
+#define ERTS_POLL_USE_SELECT_EVS 0
+
+#define ERTS_POLL_USE_KERNEL_POLL ERTS_KERNEL_POLL_VERSION
+
+#if ERTS_ENABLE_KERNEL_POLL
+#  if defined(HAVE_SYS_EVENT_H)
+#    undef ERTS_POLL_USE_KQUEUE_EVS
+#    define ERTS_POLL_USE_KQUEUE_EVS 1
+#    undef ERTS_POLL_USE_KQUEUE
+#    define ERTS_POLL_USE_KQUEUE ERTS_KERNEL_POLL_VERSION
+#  elif defined(HAVE_SYS_EPOLL_H)
+#    undef ERTS_POLL_USE_EPOLL_EVS
+#    define ERTS_POLL_USE_EPOLL_EVS 1
+#    undef ERTS_POLL_USE_EPOLL
+#    define ERTS_POLL_USE_EPOLL ERTS_KERNEL_POLL_VERSION
+#  elif defined(HAVE_SYS_DEVPOLL_H)
+#    undef ERTS_POLL_USE_DEVPOLL_EVS
+#    define ERTS_POLL_USE_DEVPOLL_EVS 1
+#    undef ERTS_POLL_USE_DEVPOLL
+#    define ERTS_POLL_USE_DEVPOLL ERTS_KERNEL_POLL_VERSION
+#  else
+#    error "Missing kernel poll implementation of erts_poll()"
+#  endif
 #endif
 
-#define ERTS_POLL_USE_FALLBACK (ERTS_POLL_USE_KQUEUE || ERTS_POLL_USE_EPOLL)
-
-#if !ERTS_POLL_USE_KERNEL_POLL || ERTS_POLL_USE_FALLBACK
+#if ERTS_NO_KERNEL_POLL_VERSION
 #  if defined(ERTS_USE_POLL)
+#    undef ERTS_POLL_USE_POLL_EVS
+#    define ERTS_POLL_USE_POLL_EVS 1
 #    undef ERTS_POLL_USE_POLL
 #    define ERTS_POLL_USE_POLL 1
 #  elif !defined(__WIN32__)
+#    undef ERTS_POLL_USE_SELECT_EVS
+#    define ERTS_POLL_USE_SELECT_EVS 1
 #    undef ERTS_POLL_USE_SELECT
 #    define ERTS_POLL_USE_SELECT 1
 #  endif
 #endif
 
-#define ERTS_POLL_USE_TIMERFD 0
+#define ERTS_POLL_USE_FALLBACK (ERTS_POLL_USE_KQUEUE || ERTS_POLL_USE_EPOLL)
 
 typedef Uint32 ErtsPollEvents;
-#undef ERTS_POLL_EV_E2N
+
+typedef enum {
+    ERTS_POLL_OP_ADD = 0,          /* Add the FD to the pollset */
+    ERTS_POLL_OP_MOD = 1,          /* Modify the FD in the pollset */
+    ERTS_POLL_OP_DEL = 2           /* Delete the FD from the pollset */
+} ErtsPollOp;
+
+#define op2str(op) (op == ERTS_POLL_OP_ADD ? "add" :            \
+                    (op == ERTS_POLL_OP_MOD ? "mod" : "del"))
 
 #if defined(__WIN32__)	/* --- win32  --------------------------------------- */
 
-#define ERTS_POLL_EV_IN   1
-#define ERTS_POLL_EV_OUT  2
-#define ERTS_POLL_EV_ERR  4
-#define ERTS_POLL_EV_NVAL 8
+#define ERTS_POLL_EV_IN    1
+#define ERTS_POLL_EV_OUT   2
+#define ERTS_POLL_EV_ERR   4
+#define ERTS_POLL_EV_NVAL  8
 
-#elif ERTS_POLL_USE_EPOLL	/* --- epoll ------------------------------- */
+#define ERTS_POLL_EV_E2N(EV) 		(EV)
+#define ERTS_POLL_EV_N2E(EV) 		(EV)
 
-#include <sys/epoll.h>
+#elif ERTS_POLL_USE_EPOLL_EVS	/* --- epoll ------------------------------- */
 
-#ifdef HAVE_SYS_TIMERFD_H
-#include <sys/timerfd.h>
-#undef ERTS_POLL_USE_TIMERFD
-#define ERTS_POLL_USE_TIMERFD 1
-#endif
+#include <sys/epoll.h>
 
 #define ERTS_POLL_EV_E2N(EV) \
   ((uint32_t) (EV))
 #define ERTS_POLL_EV_N2E(EV) \
-  ((ErtsPollEvents) (EV))
+  ((ErtsPollEvents) (EV) & ~EPOLLONESHOT)
 
 #define ERTS_POLL_EV_IN			ERTS_POLL_EV_N2E(EPOLLIN)
 #define ERTS_POLL_EV_OUT		ERTS_POLL_EV_N2E(EPOLLOUT)
 #define ERTS_POLL_EV_NVAL		ERTS_POLL_EV_N2E(EPOLLET)
 #define ERTS_POLL_EV_ERR		ERTS_POLL_EV_N2E(EPOLLERR|EPOLLHUP)
 
-#elif ERTS_POLL_USE_DEVPOLL	/* --- devpoll ----------------------------- */
+typedef struct epoll_event ErtsPollResFd;
+
+#define ERTS_POLL_RES_GET_FD(evt) ((ErtsSysFdType)((evt)->data.fd))
+#define ERTS_POLL_RES_SET_FD(evt, ident) (evt)->data.fd = ident
+#define ERTS_POLL_RES_GET_EVTS(evt) ERTS_POLL_EV_N2E((evt)->events)
+#define ERTS_POLL_RES_SET_EVTS(evt, evts) (evt)->events = ERTS_POLL_EV_E2N(evts)
+
+#elif ERTS_POLL_USE_DEVPOLL_EVS	/* --- devpoll ----------------------------- */
 
 #include <sys/devpoll.h>
 
@@ -145,12 +187,37 @@ typedef Uint32 ErtsPollEvents;
 #define ERTS_POLL_EV_NVAL		ERTS_POLL_EV_N2E(POLLNVAL)
 #define ERTS_POLL_EV_ERR		ERTS_POLL_EV_N2E(POLLERR|POLLHUP)
 
-#elif ERTS_POLL_USE_KQUEUE	/* --- kqueue ------------------------------ */
+typedef struct pollfd ErtsPollResFd;
+
+#define ERTS_POLL_RES_GET_FD(evt) ((ErtsSysFdType)((evt)->fd))
+#define ERTS_POLL_RES_SET_FD(evt, ident) (evt)->fd = ident
+#define ERTS_POLL_RES_GET_EVTS(evt) ERTS_POLL_EV_N2E((evt)->revents)
+#define ERTS_POLL_RES_SET_EVTS(evt, evts) (evt)->revents = ERTS_POLL_EV_E2N(evts)
+
+#elif ERTS_POLL_USE_KQUEUE_EVS	/* --- kqueue ------------------------------ */
 /* Kqueue use fallback defines (poll() or select()) */
+
+#include <sys/event.h>
+
+#ifdef ERTS_USE_POLL
+#  undef ERTS_POLL_USE_POLL_EVS
+#  define ERTS_POLL_USE_POLL_EVS   1
+#elif !defined(__WIN32__)
+#  undef ERTS_POLL_USE_SELECT_EVS
+#  define ERTS_POLL_USE_SELECT_EVS 1
 #endif
 
-#if ERTS_POLL_USE_POLL	/* --- poll -------------------------------- */
+typedef struct kevent ErtsPollResFd;
+
+#define ERTS_POLL_RES_GET_FD(evt) ((ErtsSysFdType)((evt)->ident))
+#define ERTS_POLL_RES_SET_FD(evt, fd) (evt)->ident = fd
+#define ERTS_POLL_RES_GET_EVTS(evt) ERTS_POLL_EV_N2E((ErtsPollEvents)(evt)->udata)
+#define ERTS_POLL_RES_SET_EVTS(evt, evts) (evt)->udata = (void*)(UWord)(ERTS_POLL_EV_E2N(evts))
+
+#endif
 
+#if ERTS_POLL_USE_POLL_EVS
+				/* --- poll -------------------------------- */
 #include <poll.h>
 
 #define ERTS_POLL_EV_NKP_E2N(EV) \
@@ -169,7 +236,7 @@ typedef Uint32 ErtsPollEvents;
 #define ERTS_POLL_EV_NKP_NVAL		ERTS_POLL_EV_N2E(POLLNVAL)
 #define ERTS_POLL_EV_NKP_ERR		ERTS_POLL_EV_N2E(POLLERR|POLLHUP)
 
-#elif ERTS_POLL_USE_SELECT	/* --- select ------------------------------ */
+#elif ERTS_POLL_USE_SELECT_EVS	/* --- select ------------------------------ */
 
 #define ERTS_POLL_EV_NKP_E2N(EV) (EV)
 #define ERTS_POLL_EV_NKP_N2E(EV) (EV)
@@ -195,70 +262,65 @@ typedef Uint32 ErtsPollEvents;
 
 #endif
 
-typedef struct ErtsPollSet_ *ErtsPollSet;
+#if !ERTS_ENABLE_KERNEL_POLL
 
-typedef struct {
-    ErtsSysFdType fd;
-    ErtsPollEvents events;
-    int on;
-} ErtsPollControlEntry;
-
-typedef struct {
+typedef struct _ErtsPollResFd {
     ErtsSysFdType fd;
     ErtsPollEvents events;
 } ErtsPollResFd;
 
+#define ERTS_POLL_RES_GET_FD(evt) (evt)->fd
+#define ERTS_POLL_RES_SET_FD(evt, ident) (evt)->fd = (ident)
+#define ERTS_POLL_RES_GET_EVTS(evt) ERTS_POLL_EV_N2E((evt)->events)
+#define ERTS_POLL_RES_SET_EVTS(evt, evts) (evt)->events = ERTS_POLL_EV_E2N(evts)
+
+#endif
+
+#define ERTS_POLL_EV_NONE (UINT_MAX & ~(ERTS_POLL_EV_IN|ERTS_POLL_EV_OUT|ERTS_POLL_EV_NVAL|ERTS_POLL_EV_ERR))
+
+#define ev2str(ev)                                                     \
+    (((ev) == 0 || (ev) == ERTS_POLL_EV_NONE) ? "NONE" :               \
+     ((ev) == ERTS_POLL_EV_IN ? "IN" :                                 \
+      ((ev) == ERTS_POLL_EV_OUT ? "OUT" :                              \
+       ((ev) == (ERTS_POLL_EV_IN|ERTS_POLL_EV_OUT) ? "IN|OUT" :        \
+        ((ev) & ERTS_POLL_EV_ERR ? "ERR" :                             \
+         ((ev) & ERTS_POLL_EV_NVAL ? "NVAL" : "OTHER"))))))
+
+
+typedef struct ERTS_POLL_EXPORT(erts_pollset) ErtsPollSet;
+
 typedef struct {
     char *primary;
-    char *fallback;
     char *kernel_poll;
     Uint memory_size;
-    int poll_set_size;
-    int fallback_poll_set_size;
+    Uint poll_set_size;
     int lazy_updates;
-    int pending_updates;
+    Uint pending_updates;
     int batch_updates;
     int concurrent_updates;
-    int max_fds;
-#ifdef ERTS_POLL_COUNT_AVOIDED_WAKEUPS
-    long no_avoided_wakeups;
-    long no_avoided_interrupts;
-    long no_interrupt_timed;
-#endif
+    int is_fallback;
+    Uint max_fds;
+    Uint active_fds;
+    Uint poll_threads;
 } ErtsPollInfo;
 
-void		ERTS_POLL_EXPORT(erts_poll_interrupt)(ErtsPollSet,
-						      int);
-void		ERTS_POLL_EXPORT(erts_poll_interrupt_timed)(ErtsPollSet,
-							    int,
-							    ErtsMonotonicTime);
-ErtsPollEvents	ERTS_POLL_EXPORT(erts_poll_control)(ErtsPollSet,
-						    ErtsSysFdType,
-						    ErtsPollEvents,
-						    int on,
-						    int* wake_poller
-						    );
-void		ERTS_POLL_EXPORT(erts_poll_controlv)(ErtsPollSet,
-						     ErtsPollControlEntry [],
-						     int on);
-int		ERTS_POLL_EXPORT(erts_poll_wait)(ErtsPollSet,
-						 ErtsPollResFd [],
-						 int *,
-						 ErtsMonotonicTime);
-int		ERTS_POLL_EXPORT(erts_poll_max_fds)(void);
-void		ERTS_POLL_EXPORT(erts_poll_info)(ErtsPollSet,
-						 ErtsPollInfo *);
-ErtsPollSet	ERTS_POLL_EXPORT(erts_poll_create_pollset)(void);
-void		ERTS_POLL_EXPORT(erts_poll_destroy_pollset)(ErtsPollSet);
-void		ERTS_POLL_EXPORT(erts_poll_init)(void);
-void		ERTS_POLL_EXPORT(erts_poll_get_selected_events)(ErtsPollSet,
-								ErtsPollEvents [],
-								int);
+#if defined(ERTS_POLL_USE_FALLBACK) && ERTS_KERNEL_POLL_VERSION
+#  undef ERTS_POLL_EXPORT
+#  define ERTS_POLL_EXPORT(FUNC) FUNC ## _flbk
+#  include "erl_poll_api.h"
+#  undef ERTS_POLL_EXPORT
+#  define ERTS_POLL_EXPORT(FUNC) FUNC
+#elif !defined(ERTS_POLL_USE_FALLBACK)
+#  define ERTS_POLL_USE_FALLBACK 0
+#endif
 
-int erts_poll_new_table_len(int old_len, int need_len);
+#include "erl_poll_api.h"
 
-#ifdef ERTS_ENABLE_LOCK_COUNT
-void ERTS_POLL_EXPORT(erts_lcnt_update_pollset_locks)(int enable);
-#endif
+/**
+ * Get the next size of the array that holds the file descriptors.
+ * This function is used in order for the check io array and the
+ * pollset array to be of the same size.
+ */
+int erts_poll_new_table_len(int old_len, int need_len);
 
 #endif /* #ifndef ERL_POLL_H__ */
diff --git a/erts/emulator/sys/common/erl_poll_api.h b/erts/emulator/sys/common/erl_poll_api.h
new file mode 100644
index 0000000000..04beb37d1c
--- /dev/null
+++ b/erts/emulator/sys/common/erl_poll_api.h
@@ -0,0 +1,122 @@
+/*
+ * %CopyrightBegin%
+ *
+ * Copyright Ericsson AB 2006-2016. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * %CopyrightEnd%
+ */
+/**
+ * @description: Poll interface functions
+ * @author Lukas Larsson
+ *
+ * The functions in the header are used to interact with the poll
+ * implementation. Iff the kernel-poll implementation needs a fallback
+ * pollset, then all functions are exported twice. Once with a _flbk
+ * suffix and once without any suffix. If no fallback is needed, then
+ * only the non-suffix version is exported.
+ */
+
+/**
+ * Initialize the poll implementation. Has to be called before any other function.
+ * @param[out] concurrent_waiters if not NULL, set to 1 if more then one thread
+ * is allowed to wait in the pollsets at the same time.
+ */
+void ERTS_POLL_EXPORT(erts_poll_init)(int *concurrent_waiters);
+/**
+ * @brief Create a new pollset.
+ * @param id The unique debug id of this pollset.
+ */
+ErtsPollSet *ERTS_POLL_EXPORT(erts_poll_create_pollset)(int id);
+
+/**
+ * Modify the contents of a pollset. This function can be called while one
+ * (or possibly more) thread is waiting in the pollset.
+ *
+ * @param ps the pollset to modify
+ * @param fd the file descriptor to modify
+ * @param op the type of operation to do. Normal usage is ADD,MOD...MOD,DEL.
+ * @param evts the events that we are changing interest to. Ignored if op is DEL.
+ * @param[in] wake_poller if set to 1 any thread waiting in the pollset will be woken.
+ *   This parameter is ignored if the pollset supports concurrent waiters.
+ * @param[out] wake_poller set to 1 if the waiting thread was woken.
+ * @return The events set, or ERTS_POLL_EV_NVAL if it was not possible to add the
+ * fd to the pollset.
+ */
+ErtsPollEvents ERTS_POLL_EXPORT(erts_poll_control)(ErtsPollSet *ps,
+                                                   ErtsSysFdType fd,
+                                                   ErtsPollOp op,
+                                                   ErtsPollEvents evts,
+                                                   int *wake_poller);
+
+/**
+ * Wait for events to be ready in the pollset. If the erts_poll_init call
+ * set concurrent_waiters to 1, then multiple threads are allowed to call
+ * this function at the same time.
+ *
+ * When an event has been triggered on a fd, that event is disabled. To
+ * re-enable it the implementation has to call erts_poll_control again.
+ *
+ * @param ps the pollset to wait for events in
+ * @param res an array of fd results that the ready fds are put in.
+ * @param[in] length the length of the res array
+ * @param[out] length the number of ready events returned in res
+ * @return 0 on success, else the ERRNO of the error that happened.
+ */
+int ERTS_POLL_EXPORT(erts_poll_wait)(ErtsPollSet *ps,
+                                     ErtsPollResFd res[],
+                                     int *length);
+/**
+ * Interrupt the thread waiting in the pollset. This function should be called
+ * with set = 0 before any thread calls erts_poll_wait in order to clear any
+ * interrupts that have happened while the thread was awake.
+ *
+ * This function has no effect on pollsets that support concurrent waiters.
+ *
+ * @param ps the pollset to wake
+ * @param set if 1, interrupt the pollset, if 0 clear the interrupt flag.
+ */
+void ERTS_POLL_EXPORT(erts_poll_interrupt)(ErtsPollSet *ps, int set);
+
+/* Debug functions */
+
+/**
+ * Get the maximum number of fds supported by the pollset
+ */
+int ERTS_POLL_EXPORT(erts_poll_max_fds)(void);
+/**
+ * Get information about the given pollset
+ */
+void ERTS_POLL_EXPORT(erts_poll_info)(ErtsPollSet *ps,
+                                      ErtsPollInfo *info);
+/**
+ * Get information about which events are currently selected.
+ *
+ * The unix fd is used to index into the array, so naturally this function does
+ * not work on windows. If the pollset cannot figure out what the selected
+ * events for a given fd is, it is set to ERTS_POLL_EV_NONE.
+ *
+ * @param ps the pollset to get events from
+ * @param evts an array of which events are selected on.
+ */
+void ERTS_POLL_EXPORT(erts_poll_get_selected_events)(ErtsPollSet *ps,
+                                                     ErtsPollEvents evts[],
+                                                     int length);
+
+#ifdef ERTS_ENABLE_LOCK_COUNT
+/**
+ * Enable lock counting of any locks within the pollset.
+ */
+void ERTS_POLL_EXPORT(erts_lcnt_enable_pollset_lock_count)(ErtsPollSet *, int enable);
+#endif
diff --git a/erts/emulator/sys/common/erl_sys_common_misc.c b/erts/emulator/sys/common/erl_sys_common_misc.c
index 09237c81ce..420138ff0a 100644
--- a/erts/emulator/sys/common/erl_sys_common_misc.c
+++ b/erts/emulator/sys/common/erl_sys_common_misc.c
@@ -45,14 +45,6 @@
 #endif
 #endif
 
-/*
- * erts_check_io_time is used by the erl_check_io implementation. The
- * global erts_check_io_time variable is declared here since there
- * (often) exist two versions of erl_check_io (kernel-poll and
- * non-kernel-poll), and we dont want two versions of this variable.
- */
-erts_atomic_t erts_check_io_time;
-
 /* Written once and only once */
 
 static int filename_encoding = ERL_FILENAME_UNKNOWN;
diff --git a/erts/emulator/sys/unix/sys.c b/erts/emulator/sys/unix/sys.c
index d05028cabc..6315135151 100644
--- a/erts/emulator/sys/unix/sys.c
+++ b/erts/emulator/sys/unix/sys.c
@@ -131,121 +131,6 @@ static int replace_intr = 0;
 /* assume yes initially, ttsl_init will clear it */
 int using_oldshell = 1;
 
-#ifdef ERTS_ENABLE_KERNEL_POLL
-
-int erts_use_kernel_poll = 0;
-
-struct {
-    int (*select)(ErlDrvPort, ErlDrvEvent, int, int);
-    int (*enif_select)(ErlNifEnv*, ErlNifEvent, enum ErlNifSelectFlags, void*, const ErlNifPid*, Eterm);
-    int (*event)(ErlDrvPort, ErlDrvEvent, ErlDrvEventData);
-    void (*check_io_as_interrupt)(void);
-    void (*check_io_interrupt)(int);
-    void (*check_io_interrupt_tmd)(int, ErtsMonotonicTime);
-    void (*check_io)(int);
-    Uint (*size)(void);
-    Eterm (*info)(void *);
-    int (*check_io_debug)(ErtsCheckIoDebugInfo *);
-} io_func = {0};
-
-
-int
-driver_select(ErlDrvPort port, ErlDrvEvent event, int mode, int on)
-{
-    return (*io_func.select)(port, event, mode, on);
-}
-
-int
-driver_event(ErlDrvPort port, ErlDrvEvent event, ErlDrvEventData event_data)
-{
-    return (*io_func.event)(port, event, event_data);
-}
-
-int enif_select(ErlNifEnv* env, ErlNifEvent event,
-                enum ErlNifSelectFlags flags, void* obj, const ErlNifPid* pid, Eterm ref)
-{
-    return (*io_func.enif_select)(env, event, flags, obj, pid, ref);
-}
-
-
-Eterm erts_check_io_info(void *p)
-{
-    return (*io_func.info)(p);
-}
-
-int
-erts_check_io_debug(ErtsCheckIoDebugInfo *ip)
-{
-    return (*io_func.check_io_debug)(ip);
-}
-
-
-static void
-init_check_io(void)
-{
-    if (erts_use_kernel_poll) {
-	io_func.select			= driver_select_kp;
-        io_func.enif_select		= enif_select_kp;
-	io_func.event			= driver_event_kp;
-	io_func.check_io_interrupt	= erts_check_io_interrupt_kp;
-	io_func.check_io_interrupt_tmd	= erts_check_io_interrupt_timed_kp;
-	io_func.check_io		= erts_check_io_kp;
-	io_func.size			= erts_check_io_size_kp;
-	io_func.info			= erts_check_io_info_kp;
-	io_func.check_io_debug		= erts_check_io_debug_kp;
-	erts_init_check_io_kp();
-	max_files = erts_check_io_max_files_kp();
-    }
-    else {
-	io_func.select			= driver_select_nkp;
-        io_func.enif_select		= enif_select_nkp;
-	io_func.event			= driver_event_nkp;
-	io_func.check_io_interrupt	= erts_check_io_interrupt_nkp;
-	io_func.check_io_interrupt_tmd	= erts_check_io_interrupt_timed_nkp;
-	io_func.check_io		= erts_check_io_nkp;
-	io_func.size			= erts_check_io_size_nkp;
-	io_func.info			= erts_check_io_info_nkp;
-	io_func.check_io_debug		= erts_check_io_debug_nkp;
-	erts_init_check_io_nkp();
-	max_files = erts_check_io_max_files_nkp();
-    }
-}
-
-#define ERTS_CHK_IO_AS_INTR()	(*io_func.check_io_interrupt)(1)
-#define ERTS_CHK_IO_INTR	(*io_func.check_io_interrupt)
-#define ERTS_CHK_IO_INTR_TMD	(*io_func.check_io_interrupt_tmd)
-#define ERTS_CHK_IO		(*io_func.check_io)
-#define ERTS_CHK_IO_SZ		(*io_func.size)
-
-#else /* !ERTS_ENABLE_KERNEL_POLL */
-
-static void
-init_check_io(void)
-{
-    erts_init_check_io();
-    max_files = erts_check_io_max_files();
-}
-
-#define ERTS_CHK_IO_AS_INTR()	erts_check_io_interrupt(1)
-#define ERTS_CHK_IO_INTR	erts_check_io_interrupt
-#define ERTS_CHK_IO_INTR_TMD	erts_check_io_interrupt_timed
-#define ERTS_CHK_IO		erts_check_io
-#define ERTS_CHK_IO_SZ		erts_check_io_size
-
-#endif
-
-void
-erts_sys_schedule_interrupt(int set)
-{
-    ERTS_CHK_IO_INTR(set);
-}
-
-void
-erts_sys_schedule_interrupt_timed(int set, ErtsMonotonicTime timeout_time)
-{
-    ERTS_CHK_IO_INTR_TMD(set, timeout_time);
-}
-
 UWord
 erts_sys_get_page_size(void)
 {
@@ -261,7 +146,7 @@ erts_sys_get_page_size(void)
 Uint
 erts_sys_misc_mem_sz(void)
 {
-    Uint res = ERTS_CHK_IO_SZ();
+    Uint res = erts_check_io_size();
     res += erts_atomic_read_mb(&sys_misc_mem_sz);
     return res;
 }
@@ -618,14 +503,12 @@ break_requested(void)
    * just set a flag - checked for and handled by
    * scheduler threads erts_check_io() (not signal handler).
    */
-#ifdef DEBUG			
-  fprintf(stderr,"break!\n");
-#endif
   if (ERTS_BREAK_REQUESTED)
       erts_exit(ERTS_INTR_EXIT, "");
 
   ERTS_SET_BREAK_REQUESTED;
-  ERTS_CHK_IO_AS_INTR(); /* Make sure we don't sleep in poll */
+  /* Wake aux thread to get handle break */
+  erts_aux_thread_poke();
 }
 
 static RETSIGTYPE request_break(int signum)
@@ -813,7 +696,7 @@ erts_sys_unix_later_init(void)
 
 int sys_max_files(void)
 {
-   return(max_files);
+   return max_files;
 }
 
 /************************** OS info *******************************/
@@ -1190,20 +1073,6 @@ erl_debug(char* fmt, ...)
 
 #endif /* DEBUG */
 
-/*
- * Called from schedule() when it runs out of runnable processes,
- * or when Erlang code has performed INPUT_REDUCTIONS reduction
- * steps. runnable == 0 iff there are no runnable Erlang processes.
- */
-void
-erl_sys_schedule(int runnable)
-{
-    ERTS_CHK_IO(!runnable);
-    ERTS_LC_ASSERT(!erts_thr_progress_is_blocking());
-}
-
-
-
 static erts_tid_t sig_dispatcher_tid;
 
 static void
@@ -1392,99 +1261,18 @@ erts_sys_main_thread(void)
 }
 
 
-#ifdef ERTS_ENABLE_KERNEL_POLL /* get_value() is currently only used when
-				  kernel-poll is enabled */
-
-/* Get arg marks argument as handled by
-   putting NULL in argv */
-static char *
-get_value(char* rest, char** argv, int* ip)
-{
-    char *param = argv[*ip]+1;
-    argv[*ip] = NULL;
-    if (*rest == '\0') {
-	char *next = argv[*ip + 1];
-	if (next[0] == '-'
-	    && next[1] == '-'
-	    &&  next[2] == '\0') {
-	    erts_fprintf(stderr, "bad \"%s\" value: \n", param);
-	    erts_usage();
-	}
-	(*ip)++;
-	argv[*ip] = NULL;
-	return next;
-    }
-    return rest;
-}
-
-#endif /* ERTS_ENABLE_KERNEL_POLL */
-
 void
 erl_sys_args(int* argc, char** argv)
 {
-    int i, j;
 
     erts_rwmtx_init(&environ_rwmtx, "environ", NIL,
         ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_GENERIC);
 
-    i = 1;
-
     ASSERT(argc && argv);
 
-    while (i < *argc) {
-	if(argv[i][0] == '-') {
-	    switch (argv[i][1]) {
-#ifdef ERTS_ENABLE_KERNEL_POLL
-	    case 'K': {
-		char *arg = get_value(argv[i] + 2, argv, &i);
-		if (strcmp("true", arg) == 0) {
-		    erts_use_kernel_poll = 1;
-		}
-		else if (strcmp("false", arg) == 0) {
-		    erts_use_kernel_poll = 0;
-		}
-		else {
-		    erts_fprintf(stderr, "bad \"K\" value: %s\n", arg);
-		    erts_usage();
-		}
-		break;
-	    }
-#endif
-	    case '-':
-		goto done_parsing;
-	    default:
-		break;
-	    }
-	}
-	i++;
-    }
-
- done_parsing:
-
-#ifdef ERTS_ENABLE_KERNEL_POLL
-    if (erts_use_kernel_poll) {
-	char no_kp[10];
-	size_t no_kp_sz = sizeof(no_kp);
-	int res = erts_sys_getenv_raw("ERL_NO_KERNEL_POLL", no_kp, &no_kp_sz);
-	if (res > 0
-	    || (res == 0
-		&& sys_strcmp("false", no_kp) != 0
-		&& sys_strcmp("FALSE", no_kp) != 0)) {
-	    erts_use_kernel_poll = 0;
-	}
-    }
-#endif
-
-    init_check_io();
+    max_files = erts_check_io_max_files();
 
     init_smp_sig_notify();
     init_smp_sig_suspend();
 
-    /* Handled arguments have been marked with NULL. Slide arguments
-       not handled towards the beginning of argv. */
-    for (i = 0, j = 0; i < *argc; i++) {
-	if (argv[i])
-	    argv[j++] = argv[i];
-    }
-    *argc = j;
 }
diff --git a/erts/emulator/sys/unix/sys_drivers.c b/erts/emulator/sys/unix/sys_drivers.c
index 7c9a532fed..0228e1af54 100644
--- a/erts/emulator/sys/unix/sys_drivers.c
+++ b/erts/emulator/sys/unix/sys_drivers.c
@@ -1723,8 +1723,6 @@ static ErlDrvData forker_start(ErlDrvPort port_num, char* name,
 
     SET_NONBLOCKING(forker_fd);
 
-    driver_select(port_num, forker_fd, ERL_DRV_READ|ERL_DRV_USE, 1);
-
     return (ErlDrvData)port_num;
 }
 
@@ -1821,10 +1819,19 @@ static void forker_ready_output(ErlDrvData e, ErlDrvEvent fd)
 static ErlDrvSSizeT forker_control(ErlDrvData e, unsigned int cmd, char *buf,
                                    ErlDrvSizeT len, char **rbuf, ErlDrvSizeT rlen)
 {
+    static int first_call = 1;
     ErtsSysForkerProto *proto = (ErtsSysForkerProto *)buf;
     ErlDrvPort port_num = (ErlDrvPort)e;
     int res;
 
+    if (first_call) {
+        /*
+         * Do driver_select here when schedulers and their pollsets have started.
+         */
+        driver_select(port_num, forker_fd, ERL_DRV_READ|ERL_DRV_USE, 1);
+        first_call = 0;
+    }
+
     driver_enq(port_num, buf, len);
     if (driver_sizeq(port_num) > sizeof(*proto)) {
         return 0;
diff --git a/erts/emulator/sys/win32/erl_poll.c b/erts/emulator/sys/win32/erl_poll.c
index 0bd43bb4fb..fd4c745c3b 100644
--- a/erts/emulator/sys/win32/erl_poll.c
+++ b/erts/emulator/sys/win32/erl_poll.c
@@ -34,6 +34,7 @@
  */
 
 /*#define HARDDEBUG */
+/*#define HARDTRACE */
 #ifdef HARDDEBUG
 #ifdef HARDTRACE
 #define HARDTRACEF(X) my_debug_printf##X
@@ -50,7 +51,7 @@ static void my_debug_printf(char *fmt, ...)
     va_start(args, fmt);
     erts_vsnprintf(buffer,1024,fmt,args);
     va_end(args);
-    erts_fprintf(stderr,"%s\r\n",buffer);
+    erts_printf("%s\r\n",buffer);
 }
 #else
 #define HARDTRACEF(X)
@@ -274,20 +275,17 @@ typedef struct _Waiter {
 /*
  * The structure for a pollset. There can currently be only one...
  */
-struct ErtsPollSet_ {
+struct erts_pollset {
     Waiter** waiter;
     int allocated_waiters;  /* Size ow waiter array */ 
     int num_waiters;	    /* Number of waiter threads. */
-    int restore_events;        /* Tells us to restore waiters events 
-				  next time around */
     HANDLE event_io_ready;     /* To be used when waiting for io */
     /* These are used to wait for workers to enter standby */
     volatile int standby_wait_counter; /* Number of threads to wait for */
     CRITICAL_SECTION standby_crit;     /* CS to guard the counter */
-    HANDLE standby_wait_event;         /* Event signalled when counte == 0 */
+    HANDLE standby_wait_event;         /* Event signalled when counter == 0 */
     erts_atomic32_t wakeup_state;
     erts_mtx_t mtx;
-    erts_atomic64_t timeout_time;
 };
 
 
@@ -352,39 +350,19 @@ do { \
     wait_standby(PS); \
  } while(0)
 
-static ERTS_INLINE void
-init_timeout_time(ErtsPollSet ps)
-{
-    erts_atomic64_init_nob(&ps->timeout_time,
-			   (erts_aint64_t) ERTS_MONOTONIC_TIME_MAX);
-}
-
-static ERTS_INLINE void
-set_timeout_time(ErtsPollSet ps, ErtsMonotonicTime time)
-{
-    erts_atomic64_set_relb(&ps->timeout_time,
-			   (erts_aint64_t) time);
-}
-
-static ERTS_INLINE ErtsMonotonicTime
-get_timeout_time(ErtsPollSet ps)
-{
-    return (ErtsMonotonicTime) erts_atomic64_read_acqb(&ps->timeout_time);
-}
-
 #define ERTS_POLL_NOT_WOKEN		((erts_aint32_t) 0)
 #define ERTS_POLL_WOKEN_IO_READY	((erts_aint32_t) 1)
 #define ERTS_POLL_WOKEN_INTR		((erts_aint32_t) 2)
 #define ERTS_POLL_WOKEN_TIMEDOUT	((erts_aint32_t) 3)
 
 static ERTS_INLINE int
-is_io_ready(ErtsPollSet ps)
+is_io_ready(ErtsPollSet *ps)
 {
     return erts_atomic32_read_nob(&ps->wakeup_state) == ERTS_POLL_WOKEN_IO_READY;
 }
 
 static ERTS_INLINE void
-woke_up(ErtsPollSet ps)
+woke_up(ErtsPollSet *ps)
 {
     if (erts_atomic32_read_nob(&ps->wakeup_state) == ERTS_POLL_NOT_WOKEN)
 	erts_atomic32_cmpxchg_nob(&ps->wakeup_state,
@@ -407,7 +385,7 @@ woke_up(ErtsPollSet ps)
 }
 
 static ERTS_INLINE int
-wakeup_cause(ErtsPollSet ps)
+wakeup_cause(ErtsPollSet *ps)
 {
     int res;
     erts_aint32_t wakeup_state = erts_atomic32_read_acqb(&ps->wakeup_state);
@@ -430,46 +408,8 @@ wakeup_cause(ErtsPollSet ps)
     return res;
 }
 
-static ERTS_INLINE DWORD
-poll_wait_timeout(ErtsPollSet ps, ErtsMonotonicTime timeout_time)
-{
-    ErtsMonotonicTime current_time, diff_time, timeout;
-
-    if (timeout_time == ERTS_POLL_NO_TIMEOUT) {
-    no_timeout:
-	set_timeout_time(ps, ERTS_MONOTONIC_TIME_MIN);
-	woke_up(ps);
-	return (DWORD) 0;
-    }
-
-    current_time = erts_get_monotonic_time(NULL);
-    diff_time = timeout_time - current_time;
-    if (diff_time <= 0)
-	goto no_timeout;
-
-    /* Round up to nearest milli second */
-    timeout = (ERTS_MONOTONIC_TO_MSEC(diff_time - 1) + 1);
-    if (timeout > INT_MAX)
-	timeout = INT_MAX; /* Also prevents DWORD overflow */
-
-    set_timeout_time(ps, current_time + ERTS_MSEC_TO_MONOTONIC(timeout));
-
-    ResetEvent(ps->event_io_ready);
-    /*
-     * Since we don't know the internals of ResetEvent() we issue
-     * a memory barrier as a safety precaution ensuring that
-     * the load of wakeup_state wont be reordered with stores made
-     * by ResetEvent().
-     */
-    ERTS_THR_MEMORY_BARRIER;
-    if (erts_atomic32_read_nob(&ps->wakeup_state) != ERTS_POLL_NOT_WOKEN)
-	return (DWORD) 0;
-
-    return (DWORD) timeout;
-}
-
 static ERTS_INLINE void
-wake_poller(ErtsPollSet ps, int io_ready)
+wake_poller(ErtsPollSet *ps, int io_ready)
 {
     erts_aint32_t wakeup_state;
     if (io_ready) {
@@ -504,13 +444,13 @@ wake_poller(ErtsPollSet ps, int io_ready)
 }
 
 static ERTS_INLINE void
-reset_io_ready(ErtsPollSet ps)
+reset_io_ready(ErtsPollSet *ps)
 {
     erts_atomic32_set_nob(&ps->wakeup_state, ERTS_POLL_NOT_WOKEN);
 }
 
 static ERTS_INLINE void
-restore_io_ready(ErtsPollSet ps)
+restore_io_ready(ErtsPollSet *ps)
 {
     erts_atomic32_set_nob(&ps->wakeup_state, ERTS_POLL_WOKEN_IO_READY);
 }
@@ -520,13 +460,13 @@ restore_io_ready(ErtsPollSet ps)
  * notifying a poller thread about I/O ready.
  */
 static ERTS_INLINE void
-notify_io_ready(ErtsPollSet ps)
+notify_io_ready(ErtsPollSet *ps)
 {
     wake_poller(ps, 1);
 }
 
 static ERTS_INLINE void
-reset_interrupt(ErtsPollSet ps)
+reset_interrupt(ErtsPollSet *ps)
 {
     /* We need to keep io-ready if set */
     erts_aint32_t wakeup_state = erts_atomic32_read_nob(&ps->wakeup_state);
@@ -543,12 +483,12 @@ reset_interrupt(ErtsPollSet ps)
 }
 
 static ERTS_INLINE void
-set_interrupt(ErtsPollSet ps)
+set_interrupt(ErtsPollSet *ps)
 {
     wake_poller(ps, 0);
 }
 
-static void setup_standby_wait(ErtsPollSet ps, int num_threads)
+static void setup_standby_wait(ErtsPollSet *ps, int num_threads)
 {
     EnterCriticalSection(&(ps->standby_crit));
     ps->standby_wait_counter = num_threads;
@@ -556,7 +496,7 @@ static void setup_standby_wait(ErtsPollSet ps, int num_threads)
     LeaveCriticalSection(&(ps->standby_crit));
 }
 
-static void signal_standby(ErtsPollSet ps) 
+static void signal_standby(ErtsPollSet *ps)
 {
     EnterCriticalSection(&(ps->standby_crit));
     --(ps->standby_wait_counter);
@@ -570,7 +510,7 @@ static void signal_standby(ErtsPollSet ps)
     LeaveCriticalSection(&(ps->standby_crit));
 }
 
-static void wait_standby(ErtsPollSet ps)
+static void wait_standby(ErtsPollSet *ps)
 {
     WaitForSingleObject(ps->standby_wait_event,INFINITE);
 }
@@ -638,7 +578,7 @@ static void consistency_check(Waiter* w)
 
 #endif
 
-static void new_waiter(ErtsPollSet ps)
+static void new_waiter(ErtsPollSet *ps)
 {
     register Waiter* w;
     DWORD tid;			/* Id for thread. */
@@ -732,7 +672,7 @@ static void *break_waiter(void *param)
 static void *threaded_waiter(void *param)
 {
     register Waiter* w = (Waiter *) param;
-    ErtsPollSet ps = (ErtsPollSet) w->xdata;
+    ErtsPollSet *ps = (ErtsPollSet*) w->xdata;
 #ifdef HARD_POLL_DEBUG2
     HANDLE oold_fired[64];
     int num_oold_fired;
@@ -835,9 +775,9 @@ event_happened:
 	    ASSERT(i >= WAIT_OBJECT_0+1);
 	    i -= WAIT_OBJECT_0;
 	    ASSERT(i >= 1);
-	    w->active_events--;
 	    HARDDEBUGF(("i = %d, a,h,t = %d,%d,%d",i,
 			w->active_events, w->highwater, w->total_events));
+	    w->active_events--;
 #ifdef HARD_POLL_DEBUG2
 	    fired[num_fired++] = w->events[i];
 #endif
@@ -867,7 +807,7 @@ event_happened:
  * The actual adding and removing from pollset utilities 
  */
 
-static int set_driver_select(ErtsPollSet ps, HANDLE event, ErtsPollEvents mode)
+static int set_driver_select(ErtsPollSet *ps, HANDLE event, ErtsPollEvents mode)
 {
     int i;
     int best_waiter = -1;	/* The waiter with lowest number of events. */
@@ -957,13 +897,13 @@ static int set_driver_select(ErtsPollSet ps, HANDLE event, ErtsPollEvents mode)
 #endif
     erts_mtx_unlock(&w->mtx);
     START_WAITER(ps,w);
-    HARDDEBUGF(("add select %d %d %d %d",best_waiter,
+    HARDDEBUGF(("%d: add select %d %d %d %d", event, best_waiter,
 		w->active_events,w->highwater,w->total_events));
     return mode;
 }
 
 
-static int cancel_driver_select(ErtsPollSet ps, HANDLE event)
+static int cancel_driver_select(ErtsPollSet *ps, HANDLE event)
 {
     int i;
 
@@ -1018,7 +958,7 @@ static int cancel_driver_select(ErtsPollSet ps, HANDLE event)
  * Interface functions
  */
 
-void  erts_poll_interrupt(ErtsPollSet ps, int set /* bool */)
+void  erts_poll_interrupt(ErtsPollSet *ps, int set /* bool */)
 {
     HARDTRACEF(("In erts_poll_interrupt(%d)",set));
     if (!set)
@@ -1028,35 +968,23 @@ void  erts_poll_interrupt(ErtsPollSet ps, int set /* bool */)
     HARDTRACEF(("Out erts_poll_interrupt(%d)",set));
 }
 
-void erts_poll_interrupt_timed(ErtsPollSet ps,
-			       int set /* bool */,
-			       ErtsMonotonicTime timeout_time)
-{
-    HARDTRACEF(("In erts_poll_interrupt_timed(%d,%ld)",set,timeout_time));
-    if (!set)
-	reset_interrupt(ps);
-    else if (get_timeout_time(ps) > timeout_time)
-	set_interrupt(ps);
-    HARDTRACEF(("Out erts_poll_interrupt_timed"));
-}
-
 
 /*
  * Windows is special, there is actually only one event type, and
  * the only difference between ERTS_POLL_EV_IN and ERTS_POLL_EV_OUT
  * is which driver callback will eventually be called.
  */
-static ErtsPollEvents do_poll_control(ErtsPollSet ps,
-				      ErtsSysFdType fd,
-				      ErtsPollEvents pe,
-				      int on /* bool */)
+static ErtsPollEvents do_poll_control(ErtsPollSet *ps,
+                                      ErtsSysFdType fd,
+                                      ErtsPollOp op,
+                                      ErtsPollEvents pe)
 {
     HANDLE event = (HANDLE) fd;
     ErtsPollEvents mode;
     ErtsPollEvents result;
     ASSERT(event != INVALID_HANDLE_VALUE);
 
-    if (on) {
+    if (op != ERTS_POLL_OP_DEL) {
 	if (pe & ERTS_POLL_EV_IN || !(pe & ERTS_POLL_EV_OUT )) {
 	    mode = ERTS_POLL_EV_IN;
 	} else {
@@ -1069,51 +997,30 @@ static ErtsPollEvents do_poll_control(ErtsPollSet ps,
     return result;
 }
 
-ErtsPollEvents erts_poll_control(ErtsPollSet ps,
+ErtsPollEvents erts_poll_control(ErtsPollSet *ps,
 				 ErtsSysFdType fd,
+                                 ErtsPollOp op,
 				 ErtsPollEvents pe,
-				 int on,
 				 int* do_wake) /* In: Wake up polling thread */
 				               /* Out: Poller is woken */
 {
     ErtsPollEvents result;
-    HARDTRACEF(("In erts_poll_control(0x%08X, %u, %d)",(unsigned long) fd, (unsigned) pe, on));
+    HARDTRACEF(("In erts_poll_control(0x%08X, %s, %s)",
+                (unsigned long) fd, op2str(op), ev2str(pe)));
     ERTS_POLLSET_LOCK(ps);
-    result=do_poll_control(ps,fd,pe,on);
+    result=do_poll_control(ps, fd, op, pe);
     ERTS_POLLSET_UNLOCK(ps);
     *do_wake = 0; /* Never any need to wake polling threads on windows */
     HARDTRACEF(("Out erts_poll_control -> %u",(unsigned) result));
     return result;
 }
 
-void erts_poll_controlv(ErtsPollSet ps,
-			ErtsPollControlEntry pcev[],
-			int len)
-{
-    int i;
-    int hshur = 0;
-    int do_wake = 0;
-
-    HARDTRACEF(("In erts_poll_controlv(%d)",len));
-    ERTS_POLLSET_LOCK(ps);
-
-    for (i = 0; i < len; i++) {
-	pcev[i].events = do_poll_control(ps,
-					 pcev[i].fd,
-					 pcev[i].events,
-					 pcev[i].on);
-    }
-    ERTS_POLLSET_UNLOCK(ps);
-    HARDTRACEF(("Out erts_poll_controlv"));
-}
-
-int erts_poll_wait(ErtsPollSet ps,
+int erts_poll_wait(ErtsPollSet *ps,
 		   ErtsPollResFd pr[],
-		   int *len,
-		   ErtsMonotonicTime timeout_time)
+		   int *len)
 {
     int no_fds;
-    DWORD timeout;
+    DWORD timeout = INFINITE;
     EventData* ev;
     int res = 0;
     int num = 0;
@@ -1124,42 +1031,6 @@ int erts_poll_wait(ErtsPollSet ps,
     HARDTRACEF(("In erts_poll_wait"));
     ERTS_POLLSET_LOCK(ps);
 
-    if (!is_io_ready(ps) && ps->restore_events) {
-	HARDDEBUGF(("Restore events: %d",ps->num_waiters));
-	ps->restore_events = 0;
-	for (i = 0; i < ps->num_waiters; ++i) {
-	   Waiter* w = ps->waiter[i];
-	   erts_mtx_lock(&w->mtx);
-	   HARDDEBUGF(("Maybe reset %d %d %d %d",i,
-		       w->active_events,w->highwater,w->total_events));
-	   if (w->active_events < w->total_events) {
-	       erts_mtx_unlock(&w->mtx);
-	       STOP_WAITER(ps,w);
-	       HARDDEBUGF(("Need reset %d %d %d %d",i,
-			   w->active_events,w->highwater,w->total_events));
-	       erts_mtx_lock(&w->mtx);	       
-	       /* Need reset, just check that it doesn't have got more to tell */
-	       if (w->highwater != w->active_events) {
-		   HARDDEBUGF(("Oups!"));
-		   /* Oups, got signalled before we took the lock, can't reset */
-		   if(!is_io_ready(ps)) {
-		       erts_exit(ERTS_ERROR_EXIT,"Internal error: "
-				"Inconsistent io structures in erl_poll.\n");
-		   }
-		   START_WAITER(ps,w);
-		   erts_mtx_unlock(&w->mtx);
-		   ps->restore_events = 1; 
-		   continue;
-	       }
-	       w->active_events = w->highwater =  w->total_events;
-	       START_WAITER(ps,w);
-	       erts_mtx_unlock(&w->mtx);
-	   } else {
-	       erts_mtx_unlock(&w->mtx);
-	   }
-	}
-    }
-
     no_fds = *len;
 
 #ifdef ERTS_POLL_MAX_RES
@@ -1167,22 +1038,29 @@ int erts_poll_wait(ErtsPollSet ps,
 	no_fds = ERTS_POLL_MAX_RES;
 #endif
 
-    timeout = poll_wait_timeout(ps, timeout_time);
-
-    /*HARDDEBUGF(("timeout = %ld",(long) timeout));*/
+    ResetEvent(ps->event_io_ready);
+    /*
+     * Since we don't know the internals of ResetEvent() we issue
+     * a memory barrier as a safety precaution ensuring that
+     * the load of wakeup_state wont be reordered with stores made
+     * by ResetEvent().
+     */
+    ERTS_THR_MEMORY_BARRIER;
+    if (erts_atomic32_read_nob(&ps->wakeup_state) != ERTS_POLL_NOT_WOKEN)
+       timeout = (DWORD) 0;
 
-    if (timeout > 0 && !erts_atomic32_read_nob(&break_waiter_state)) {
+    if (!erts_atomic32_read_nob(&break_waiter_state)) {
 	HANDLE harr[2] = {ps->event_io_ready, break_happened_event};
 	int num_h = 2;
-        ERTS_MSACC_PUSH_STATE_M();
+        ERTS_MSACC_PUSH_STATE();
 
 	HARDDEBUGF(("Start waiting %d [%d]",num_h, (int) timeout));
 	ERTS_POLLSET_UNLOCK(ps);
 	erts_thr_progress_prepare_wait(NULL);
-        ERTS_MSACC_SET_STATE_CACHED_M(ERTS_MSACC_STATE_SLEEP);
+        ERTS_MSACC_SET_STATE_CACHED(ERTS_MSACC_STATE_SLEEP);
 	WaitForMultipleObjects(num_h, harr, FALSE, timeout);
 	erts_thr_progress_finalize_wait(NULL);
-        ERTS_MSACC_POP_STATE_M();
+        ERTS_MSACC_POP_STATE();
 	ERTS_POLLSET_LOCK(ps);
 	HARDDEBUGF(("Stop waiting %d [%d]",num_h, (int) timeout));
 	woke_up(ps);
@@ -1215,7 +1093,7 @@ int erts_poll_wait(ErtsPollSet ps,
 
     reset_io_ready(ps);
 
-    n = ps->num_waiters;	
+    n = ps->num_waiters;
 
     for (i = 0; i < n; i++) {
 	Waiter* w = ps->waiter[i];
@@ -1241,11 +1119,10 @@ int erts_poll_wait(ErtsPollSet ps,
 		HARDDEBUGF(("To many FD's to report!"));
 		goto done;
 	    }
-	    HARDDEBUGF(("SET! Restore events"));
-	    ps->restore_events = 1;
 	    HARDDEBUGF(("Report %d,%d",i,j));
-	    pr[num].fd = (ErtsSysFdType) w->events[j];
-	    pr[num].events = w->evdata[j]->mode;
+	    ERTS_POLL_RES_SET_FD(&pr[num], w->events[j]);
+	    ERTS_POLL_RES_SET_EVTS(&pr[num], w->evdata[j]->mode);
+            remove_event_from_set(w, j);
 #ifdef HARD_POLL_DEBUG
 	    poll_debug_reported(w->events[j],w->highwater | (j << 16));
 	    poll_debug_reported(w->events[j],first | (last << 16));
@@ -1253,13 +1130,14 @@ int erts_poll_wait(ErtsPollSet ps,
 	    ++num;
 	}
 
+        w->total_events = w->highwater = w->active_events;
+
 #ifdef DEBUG
 	consistency_check(w);
 #endif
 	erts_mtx_unlock(&w->mtx);
     }
  done:
-    set_timeout_time(ps, ERTS_MONOTONIC_TIME_MAX);
     *len = num;
     ERTS_POLLSET_UNLOCK(ps);
     HARDTRACEF(("Out erts_poll_wait"));
@@ -1274,7 +1152,7 @@ int erts_poll_max_fds(void)
     return res;
 }
 
-void erts_poll_info(ErtsPollSet ps,
+void erts_poll_info(ErtsPollSet *ps,
 		    ErtsPollInfo *pip)
 {
     Uint size = 0;
@@ -1284,7 +1162,7 @@ void erts_poll_info(ErtsPollSet ps,
     HARDTRACEF(("In erts_poll_info"));
     ERTS_POLLSET_LOCK(ps);
 
-    size += sizeof(struct ErtsPollSet_);
+    size += sizeof(struct erts_pollset);
     size += sizeof(Waiter *) * ps->allocated_waiters;
     for (i = 0; i < ps->num_waiters; ++i) {
 	Waiter *w = ps->waiter[i];
@@ -1299,16 +1177,12 @@ void erts_poll_info(ErtsPollSet ps,
 
     pip->primary = "WaitForMultipleObjects"; 
 
-    pip->fallback = NULL;
-
     pip->kernel_poll = NULL;
 
     pip->memory_size = size;
 
     pip->poll_set_size = num_events;
 
-    pip->fallback_poll_set_size = 0;
-
     pip->lazy_updates = 0;
 
     pip->pending_updates = 0;
@@ -1316,6 +1190,8 @@ void erts_poll_info(ErtsPollSet ps,
     pip->batch_updates = 0;
 
     pip->concurrent_updates = 0;
+
+    pip->is_fallback = 0;
     ERTS_POLLSET_UNLOCK(ps);
 
     pip->max_fds = erts_poll_max_fds();
@@ -1323,10 +1199,10 @@ void erts_poll_info(ErtsPollSet ps,
 
 }
 
-ErtsPollSet erts_poll_create_pollset(void)
+ErtsPollSet *erts_poll_create_pollset(int no)
 {
-    ErtsPollSet ps = SEL_ALLOC(ERTS_ALC_T_POLLSET,
-			       sizeof(struct ErtsPollSet_));
+    ErtsPollSet *ps = SEL_ALLOC(ERTS_ALC_T_POLLSET,
+			       sizeof(struct erts_pollset));
     HARDTRACEF(("In erts_poll_create_pollset"));
 
     ps->num_waiters = 0;
@@ -1337,17 +1213,15 @@ ErtsPollSet erts_poll_create_pollset(void)
     ps->standby_wait_counter = 0;
     ps->event_io_ready = CreateManualEvent(FALSE);
     ps->standby_wait_event = CreateManualEvent(FALSE); 
-    ps->restore_events = 0;
 
     erts_atomic32_init_nob(&ps->wakeup_state, ERTS_POLL_NOT_WOKEN);
     erts_mtx_init(&ps->mtx, "pollset", NIL, ERTS_LOCK_FLAGS_CATEGORY_IO);
-    init_timeout_time(ps);
 
     HARDTRACEF(("Out erts_poll_create_pollset"));
     return ps;
 }
 
-void erts_poll_destroy_pollset(ErtsPollSet ps)
+void erts_poll_destroy_pollset(ErtsPollSet *ps)
 {
     int i;
     HARDTRACEF(("In erts_poll_destroy_pollset"));
@@ -1378,14 +1252,16 @@ void erts_poll_destroy_pollset(ErtsPollSet ps)
 /*
  * Actually mostly initializes the friend module sys_interrupt...
  */
-void  erts_poll_init(void)
+void  erts_poll_init(int *concurrent_updates)
 {
-    erts_tid_t thread;
 
 #ifdef HARD_POLL_DEBUG
     poll_debug_init();
 #endif
 
+    if (concurrent_updates)
+        *concurrent_updates = 0;
+
     HARDTRACEF(("In erts_poll_init"));
     erts_sys_break_event = CreateManualEvent(FALSE);
 
@@ -1394,21 +1270,26 @@ void  erts_poll_init(void)
     break_happened_event = CreateManualEvent(FALSE);
     erts_atomic32_init_nob(&break_waiter_state, 0); 
 
+    HARDTRACEF(("Out erts_poll_init"));
+}
+
+void erts_poll_late_init(void)
+{
+    erts_tid_t thread;
     erts_thr_create(&thread, &break_waiter, NULL, NULL);
     ERTS_UNSET_BREAK_REQUESTED;
-    HARDTRACEF(("Out erts_poll_init"));
 }
 
 /*
  * Non windows friendly interface, not used when fd's are not continous
  */
-void  erts_poll_get_selected_events(ErtsPollSet ps,
+void  erts_poll_get_selected_events(ErtsPollSet *ps,
 				    ErtsPollEvents ev[],
 				    int len)
 {
     int i;
     HARDTRACEF(("In erts_poll_get_selected_events"));
     for (i = 0; i < len; ++i)
-	ev[i] = 0;
+	ev[i] = ERTS_POLL_EV_NONE;
     HARDTRACEF(("Out erts_poll_get_selected_events"));
 }
diff --git a/erts/emulator/sys/win32/erl_win_dyn_driver.h b/erts/emulator/sys/win32/erl_win_dyn_driver.h
index 6f28d513c2..0d1a6d4c87 100644
--- a/erts/emulator/sys/win32/erl_win_dyn_driver.h
+++ b/erts/emulator/sys/win32/erl_win_dyn_driver.h
@@ -40,7 +40,6 @@ WDD_TYPEDEF(int, driver_exit, (ErlDrvPort, int));
 WDD_TYPEDEF(int, driver_failure_eof, (ErlDrvPort));
 WDD_TYPEDEF(void, erl_drv_busy_msgq_limits, (ErlDrvPort, ErlDrvSizeT *, ErlDrvSizeT *));
 WDD_TYPEDEF(int, driver_select, (ErlDrvPort, ErlDrvEvent, int, int));
-WDD_TYPEDEF(int, driver_event, (ErlDrvPort, ErlDrvEvent,ErlDrvEventData));
 WDD_TYPEDEF(int, driver_output, (ErlDrvPort, char *, ErlDrvSizeT));
 WDD_TYPEDEF(int, driver_output2, (ErlDrvPort, char *, ErlDrvSizeT ,char *, ErlDrvSizeT));
 WDD_TYPEDEF(int, driver_output_binary, (ErlDrvPort, char *, ErlDrvSizeT, ErlDrvBinary*, ErlDrvSizeT, ErlDrvSizeT));
@@ -162,7 +161,7 @@ typedef struct {
     WDD_FTYPE(driver_failure_eof) *driver_failure_eof;
     WDD_FTYPE(erl_drv_busy_msgq_limits) *erl_drv_busy_msgq_limits;
     WDD_FTYPE(driver_select) *driver_select;
-    WDD_FTYPE(driver_event) *driver_event;
+    void *REMOVED_driver_event;
     WDD_FTYPE(driver_output) *driver_output;
     WDD_FTYPE(driver_output2) *driver_output2;
     WDD_FTYPE(driver_output_binary) *driver_output_binary;
@@ -276,7 +275,6 @@ extern TWinDynDriverCallbacks WinDynDriverCallbacks;
 #define driver_failure_eof (WinDynDriverCallbacks.driver_failure_eof)
 #define erl_drv_busy_msgq_limits (WinDynDriverCallbacks.erl_drv_busy_msgq_limits)
 #define driver_select (WinDynDriverCallbacks.driver_select)
-#define driver_event (WinDynDriverCallbacks.driver_event)
 #define driver_output (WinDynDriverCallbacks.driver_output)
 #define driver_output2 (WinDynDriverCallbacks.driver_output2)
 #define driver_output_binary (WinDynDriverCallbacks.driver_output_binary)
@@ -414,7 +412,7 @@ do {				                        \
 ((W).driver_failure_eof) = driver_failure_eof;		\
 ((W).erl_drv_busy_msgq_limits) = erl_drv_busy_msgq_limits;\
 ((W).driver_select) = driver_select;			\
-((W).driver_event) = driver_event;			\
+((W).REMOVED_driver_event) = NULL;			\
 ((W).driver_output) = driver_output;			\
 ((W).driver_output2) = driver_output2;			\
 ((W).driver_output_binary) = driver_output_binary;	\
diff --git a/erts/emulator/sys/win32/sys.c b/erts/emulator/sys/win32/sys.c
index b23dbecbac..0598a12351 100644
--- a/erts/emulator/sys/win32/sys.c
+++ b/erts/emulator/sys/win32/sys.c
@@ -3235,40 +3235,16 @@ void erl_sys_init(void)
 	SetStdHandle(STD_ERROR_HANDLE, GetStdHandle(STD_OUTPUT_HANDLE));
     }
     erts_sys_init_float();
-    erts_init_check_io();
 
     /* Suppress windows error message popups */
     SetErrorMode(SetErrorMode(0) |
 		 SEM_FAILCRITICALERRORS | SEM_NOOPENFILEERRORBOX); 
 }
+void erts_poll_late_init(void);
 
 void
 erl_sys_late_init(void)
 {
     /* do nothing */
+    erts_poll_late_init();
 }
-
-void
-erts_sys_schedule_interrupt(int set)
-{
-    erts_check_io_interrupt(set);
-}
-
-void
-erts_sys_schedule_interrupt_timed(int set, ErtsMonotonicTime timeout_time)
-{
-    erts_check_io_interrupt_timed(set, timeout_time);
-}
-
-/*
- * Called from schedule() when it runs out of runnable processes,
- * or when Erlang code has performed INPUT_REDUCTIONS reduction
- * steps. runnable == 0 iff there are no runnable Erlang processes.
- */
-void
-erl_sys_schedule(int runnable)
-{
-    erts_check_io(!runnable);
-    ERTS_LC_ASSERT(!erts_thr_progress_is_blocking());
-}
-
diff --git a/erts/emulator/test/driver_SUITE.erl b/erts/emulator/test/driver_SUITE.erl
index 5fca191679..33d0b708cf 100644
--- a/erts/emulator/test/driver_SUITE.erl
+++ b/erts/emulator/test/driver_SUITE.erl
@@ -43,9 +43,9 @@
          outputv_errors/1,
          driver_unloaded/1,
          io_ready_exit/1,
+         use_fallback_pollset/0,
          use_fallback_pollset/1,
          bad_fd_in_pollset/1,
-         driver_event/1,
          fd_change/1,
          steal_control/1,
          otp_6602/1,
@@ -58,11 +58,9 @@
          ioq_exit_ready_output/1,
          ioq_exit_timeout/1,
          ioq_exit_ready_async/1,
-         ioq_exit_event/1,
          ioq_exit_ready_input_async/1,
          ioq_exit_ready_output_async/1,
          ioq_exit_timeout_async/1,
-         ioq_exit_event_async/1,
          zero_extended_marker_garb_drv/1,
          invalid_extended_marker_drv/1,
          larger_major_vsn_drv/1,
@@ -86,6 +84,8 @@
 
 -export([bin_prefix/2]).
 
+-export([get_check_io_total/1]).   % for z_SUITE.erl
+
 -include_lib("common_test/include/ct.hrl").
 
 
@@ -119,17 +119,26 @@
 -define(heap_binary_size, 64).
 
 init_per_testcase(Case, Config) when is_atom(Case), is_list(Config) ->
-    case catch erts_debug:get_internal_state(available_internal_state) of
-        true -> ok;
-        _ -> erts_debug:set_internal_state(available_internal_state, true)
-    end,
+    CIOD = rpc(Config,
+               fun() ->
+                       case catch erts_debug:get_internal_state(available_internal_state) of
+                           true -> ok;
+                           _ -> erts_debug:set_internal_state(available_internal_state, true)
+                       end,
+                       erts_debug:get_internal_state(check_io_debug)
+               end),
     erlang:display({init_per_testcase, Case}),
-    0 = element(1, erts_debug:get_internal_state(check_io_debug)),
+    0 = element(1, CIOD),
     [{testcase, Case}|Config].
 
-end_per_testcase(Case, _Config) ->
+end_per_testcase(Case, Config) ->
     erlang:display({end_per_testcase, Case}),
-    0 = element(1, erts_debug:get_internal_state(check_io_debug)),
+    CIOD = rpc(Config,
+               fun() ->
+                       get_stable_check_io_info(),
+                       erts_debug:get_internal_state(check_io_debug)
+               end),
+    0 = element(1, CIOD),
     ok.
 
 suite() ->
@@ -137,10 +146,13 @@ suite() ->
      {timetrap, {minutes, 1}}].
 
 all() -> %% Keep a_test first and z_test last...
-    [a_test, outputv_errors, outputv_echo, queue_echo, {group, timer},
-     driver_unloaded, io_ready_exit, use_fallback_pollset,
-     bad_fd_in_pollset, driver_event, fd_change,
-     steal_control, otp_6602, driver_system_info_base_ver,
+    [a_test, outputv_errors, outputv_echo, queue_echo,
+     {group, timer},
+     driver_unloaded, io_ready_exit, otp_6602,
+     {group, polling},
+     {group, poll_thread},
+     {group, poll_set},
+     driver_system_info_base_ver,
      driver_system_info_prev_ver,
      driver_system_info_current_ver, driver_monitor,
      {group, ioq_exit}, zero_extended_marker_garb_drv,
@@ -148,7 +160,6 @@ all() -> %% Keep a_test first and z_test last...
      larger_minor_vsn_drv, smaller_major_vsn_drv,
      smaller_minor_vsn_drv, peek_non_existing_queue,
      otp_6879, caller, many_events, missing_callbacks,
-     smp_select, driver_select_use,
      thread_mseg_alloc_cache_clean,
      otp_9302,
      thr_free_drv,
@@ -161,11 +172,18 @@ groups() ->
     [{timer, [],
       [timer_measure, timer_cancel, timer_delay,
        timer_change]},
+     {poll_thread, [], [{group, polling}]},
+     {poll_set, [], [{group, polling}]},
+     {polling, [],
+      [a_test, use_fallback_pollset,
+       bad_fd_in_pollset, fd_change,
+       steal_control, smp_select,
+       driver_select_use, z_test]},
      {ioq_exit, [],
       [ioq_exit_ready_input, ioq_exit_ready_output,
-       ioq_exit_timeout, ioq_exit_ready_async, ioq_exit_event,
+       ioq_exit_timeout, ioq_exit_ready_async,
        ioq_exit_ready_input_async, ioq_exit_ready_output_async,
-       ioq_exit_timeout_async, ioq_exit_event_async]}].
+       ioq_exit_timeout_async]}].
 
 init_per_suite(Config) ->
     Config.
@@ -173,10 +191,28 @@ init_per_suite(Config) ->
 end_per_suite(_Config) ->
     catch erts_debug:set_internal_state(available_internal_state, false).
 
+init_per_group(poll_thread, Config) ->
+    [{node_args, "+IOt 2"} | Config];
+init_per_group(poll_set, Config) ->
+    [{node_args, "+IOt 2 +IOp 2"} | Config];
+init_per_group(polling, Config) ->
+    case proplists:get_value(node_args, Config) of
+        undefined ->
+            Config;
+        Args ->
+            {ok, Node} = start_node(polling, Args),
+            [{node, Node} | Config]
+    end;
 init_per_group(_GroupName, Config) ->
     Config.
 
 end_per_group(_GroupName, Config) ->
+    case proplists:get_value(node, Config) of
+        undefined ->
+            ok;
+        Node ->
+            stop_node(Node)
+    end,
     Config.
 
 %% Test sending bad types to port with an outputv-capable driver.
@@ -778,21 +814,23 @@ io_ready_exit(Config) when is_list(Config) ->
 -define(CHKIO_STOP, 0).
 -define(CHKIO_USE_FALLBACK_POLLSET, 1).
 -define(CHKIO_BAD_FD_IN_POLLSET, 2).
--define(CHKIO_DRIVER_EVENT, 3).
 -define(CHKIO_FD_CHANGE, 4).
 -define(CHKIO_STEAL, 5).
 -define(CHKIO_STEAL_AUX, 6).
 -define(CHKIO_SMP_SELECT, 7).
 -define(CHKIO_DRV_USE, 8).
 
+use_fallback_pollset() ->
+    [{timetrap, {minutes, 2}}].
+
 use_fallback_pollset(Config) when is_list(Config) ->
+    rpc(Config, fun() -> use_fallback_pollset_t(Config) end).
+
+use_fallback_pollset_t(Config) when is_list(Config) ->
     FlbkFun = fun () ->
-                      ChkIoDuring = erlang:system_info(check_io),
-                      case lists:keysearch(fallback_poll_set_size,
-                                           1,
-                                           ChkIoDuring) of
-                          {value,
-                           {fallback_poll_set_size, N}} when N > 0 ->
+                      {Flbk, _} = get_fallback(erlang:system_info(check_io)),
+                      case lists:keysearch(total_poll_set_size, 1, Flbk) of
+                          {value, {total_poll_set_size, N}} when N > 0 ->
                               ok;
                           Error ->
                               ct:fail({failed_to_use_fallback, Error})
@@ -814,6 +852,7 @@ use_fallback_pollset(Config) when is_list(Config) ->
           Skip ->
               {fun () -> ok end, Skip, ok}
       end,
+    io:format("Node = ~p~n",[node()]),
     case chkio_test_fini(chkio_test(Handel,
                                     ?CHKIO_USE_FALLBACK_POLLSET,
                                     fun () ->
@@ -825,27 +864,31 @@ use_fallback_pollset(Config) when is_list(Config) ->
     end.
 
 bad_fd_in_pollset(Config) when is_list(Config) ->
-    chkio_test_fini(chkio_test(chkio_test_init(Config),
-                               ?CHKIO_BAD_FD_IN_POLLSET,
-                               fun () -> sleep(1000) end)).
-
-driver_event(Config) when is_list(Config) ->
-    chkio_test_fini(chkio_test(chkio_test_init(Config),
-                               ?CHKIO_DRIVER_EVENT,
-                               fun () -> sleep(1000) end)).
+    rpc(Config,
+        fun() ->
+                chkio_test_fini(chkio_test(chkio_test_init(Config),
+                                           ?CHKIO_BAD_FD_IN_POLLSET,
+                                           fun () -> sleep(1000) end))
+        end).
 
 fd_change(Config) when is_list(Config) ->
-    chkio_test_fini(chkio_test(chkio_test_init(Config),
-                               ?CHKIO_FD_CHANGE,
-                               fun () -> sleep(1000) end)).
+    rpc(Config,
+        fun() ->
+                chkio_test_fini(chkio_test(chkio_test_init(Config),
+                                           ?CHKIO_FD_CHANGE,
+                                           fun () -> sleep(1000) end))
+        end).
 
 steal_control(Config) when is_list(Config) ->
-    chkio_test_fini(case chkio_test_init(Config) of
-                        {erts_poll_info, _} = Hndl ->
-                            steal_control_test(Hndl);
-                        Skip ->
-                            Skip
-                    end).
+    rpc(Config,
+        fun() ->
+                chkio_test_fini(case chkio_test_init(Config) of
+                                    {erts_poll_info, _} = Hndl ->
+                                        steal_control_test(Hndl);
+                                    Skip ->
+                                        Skip
+                                end)
+        end).
 
 steal_control_test(Hndl = {erts_poll_info, Before}) ->
     Port = open_chkio_port(),
@@ -887,7 +930,7 @@ chkio_test_init(Config) when is_list(Config) ->
     ChkIo = get_stable_check_io_info(),
     case catch lists:keysearch(name, 1, ChkIo) of
         {value, {name, erts_poll}} ->
-            io:format("Before test: ~p~n", [ChkIo]),
+            ct:log("Before test: ~p~n", [ChkIo]),
             Path = proplists:get_value(data_dir, Config),
             erl_ddll:start(),
             ok = load_driver(Path, 'chkio_drv'),
@@ -948,8 +991,9 @@ chkio_test({erts_poll_info, Before},
         "ok" ->
             chk_chkio_port(Port),
             Fun(),
-            During = erlang:system_info(check_io),
+            During = get_check_io_total(erlang:system_info(check_io)),
             erlang:display(During),
+
             0 = element(1, erts_debug:get_internal_state(check_io_debug)),
             io:format("During test: ~p~n", [During]),
             chk_chkio_port(Port),
@@ -1001,22 +1045,83 @@ verify_chkio_state(Before, After) ->
     ok.
 
 get_stable_check_io_info() ->
-    ChkIo = erlang:system_info(check_io),
-    PendUpdNo = case lists:keysearch(pending_updates, 1, ChkIo) of
-                    {value, {pending_updates, PendNo}} ->
-                        PendNo;
-                    false ->
-                        0
-                end,
-    {value, {active_fds, ActFds}} = lists:keysearch(active_fds, 1, ChkIo),
+    get_stable_check_io_info(10).
+get_stable_check_io_info(0) ->
+    get_check_io_total(erlang:system_info(check_io));
+get_stable_check_io_info(N) ->
+    ChkIo = get_check_io_total(erlang:system_info(check_io)),
+    PendUpdNo = proplists:get_value(pending_updates, ChkIo, 0),
+    ActFds = proplists:get_value(active_fds, ChkIo),
     case {PendUpdNo, ActFds} of
         {0, 0} ->
             ChkIo;
         _ ->
-            receive after 10 -> ok end,
-            get_stable_check_io_info()
+            receive after 100 -> ok end,
+            get_stable_check_io_info(N-1)
     end.
 
+%% Merge return from erlang:system_info(check_io)
+%% as if it was one big pollset.
+get_check_io_total(ChkIo) ->
+    ct:log("ChkIo = ~p~n",[ChkIo]),
+    {Fallback, Rest} = get_fallback(ChkIo),
+    add_fallback_infos(Fallback,
+      lists:foldl(fun(Pollset, Acc) ->
+                          lists:zipwith(fun(A, B) ->
+                                                add_pollset_infos(A,B)
+                                        end,
+                                        Pollset, Acc)
+                  end,
+                  hd(Rest), tl(Rest))).
+
+add_pollset_infos({Tag, A}=TA , {Tag, B}=TB) ->
+    case tag_type(Tag) of
+        sum ->
+            {Tag, A + B};
+        const ->
+            case A of
+                B -> TA;
+                _ ->
+                    ct:fail("Unexpected diff in pollsets ~p != ~p",
+                            [TA,TB])
+            end
+    end.
+
+get_fallback([MaybeFallback | ChkIo] = AllChkIo) ->
+    case proplists:get_value(fallback, MaybeFallback) of
+        true ->
+            {MaybeFallback, ChkIo};
+        false ->
+            {undefined, AllChkIo}
+    end.
+
+add_fallback_infos(undefined, Acc) ->
+    Acc;
+add_fallback_infos(Flbk, Acc) ->
+    lists:zipwith(fun({Tag, A}=TA, {Tag, B}=TB) ->
+                          case tag_type(Tag) of
+                              sum -> {Tag, A + B};
+                              const when Tag =:= fallback -> TA;
+                              const -> TB
+                          end
+                  end,
+                  Flbk, Acc).
+
+tag_type(name) -> const;
+tag_type(primary) -> const;
+tag_type(fallback) -> const;
+tag_type(kernel_poll) -> const;
+tag_type(memory_size) -> sum;
+tag_type(total_poll_set_size) -> sum;
+tag_type(lazy_updates) -> const;
+tag_type(pending_updates) -> sum;
+tag_type(batch_updates) -> const;
+tag_type(concurrent_updates) -> const;
+tag_type(max_fds) -> const;
+tag_type(active_fds) -> sum;
+tag_type(poll_threads) -> sum.
+
+
 %% Missed port lock when stealing control of fd from a
 %% driver that didn't use the same lock. The lock checker
 %% used to trigger on this and dump core.
@@ -1336,11 +1441,9 @@ driver_monitor(Config) when is_list(Config) ->
 -define(IOQ_EXIT_READY_OUTPUT, 2).
 -define(IOQ_EXIT_TIMEOUT, 3).
 -define(IOQ_EXIT_READY_ASYNC, 4).
--define(IOQ_EXIT_EVENT, 5).
 -define(IOQ_EXIT_READY_INPUT_ASYNC, 6).
 -define(IOQ_EXIT_READY_OUTPUT_ASYNC, 7).
 -define(IOQ_EXIT_TIMEOUT_ASYNC, 8).
--define(IOQ_EXIT_EVENT_ASYNC, 9).
 
 ioq_exit_test(Config, TestNo) ->
     Drv = ioq_exit_drv,
@@ -1393,9 +1496,6 @@ ioq_exit_timeout(Config) when is_list(Config) ->
 ioq_exit_ready_async(Config) when is_list(Config) ->
     ioq_exit_test(Config, ?IOQ_EXIT_READY_ASYNC).
 
-ioq_exit_event(Config) when is_list(Config) ->
-    ioq_exit_test(Config, ?IOQ_EXIT_EVENT).
-
 ioq_exit_ready_input_async(Config) when is_list(Config) ->
     ioq_exit_test(Config, ?IOQ_EXIT_READY_INPUT_ASYNC).
 
@@ -1405,9 +1505,6 @@ ioq_exit_ready_output_async(Config) when is_list(Config) ->
 ioq_exit_timeout_async(Config) when is_list(Config) ->
     ioq_exit_test(Config, ?IOQ_EXIT_TIMEOUT_ASYNC).
 
-ioq_exit_event_async(Config) when is_list(Config) ->
-    ioq_exit_test(Config, ?IOQ_EXIT_EVENT_ASYNC).
-
 
 vsn_mismatch_test(Config, LoadResult) ->
     Path = proplists:get_value(data_dir, Config),
@@ -1641,7 +1738,7 @@ missing_callbacks(Config) when is_list(Config) ->
 smp_select(Config) when is_list(Config) -> 
     case os:type() of
         {win32,_} -> {skipped, "Test not implemented for this OS"};
-        _ -> smp_select0(Config)
+        _ -> rpc(Config, fun() -> smp_select0(Config) end)
     end.
 
 smp_select0(Config) ->
@@ -1697,7 +1794,7 @@ smp_select_wait(Pids, TimeoutMsg) ->
 driver_select_use(Config) when is_list(Config) -> 
     case os:type() of
         {win32,_} -> {skipped, "Test not implemented for this OS"};
-        _ -> driver_select_use0(Config)
+        _ -> rpc(Config, fun() -> driver_select_use0(Config) end)
     end.
 
 driver_select_use0(Config) ->
@@ -2264,10 +2361,10 @@ count_proc_sched(Ps, PNs) ->
     end.
 
 a_test(Config) when is_list(Config) ->
-    check_io_debug().
+    rpc(Config, fun check_io_debug/0).
 
 z_test(Config) when is_list(Config) ->
-    check_io_debug().
+    rpc(Config, fun check_io_debug/0).
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %% 		Utilities
@@ -2275,8 +2372,8 @@ z_test(Config) when is_list(Config) ->
 
 check_io_debug() ->
     get_stable_check_io_info(),
-    {NoErrorFds, NoUsedFds, NoDrvSelStructs, NoDrvEvStructs} = CheckIoDebug
-    = erts_debug:get_internal_state(check_io_debug),
+    {NoErrorFds, NoUsedFds, NoDrvSelStructs, NoEnifSelStructs}
+        = CheckIoDebug = erts_debug:get_internal_state(check_io_debug),
     HasGetHost = has_gethost(),
     ct:log("check_io_debug: ~p~n"
            "HasGetHost: ~p",[CheckIoDebug, HasGetHost]),
@@ -2289,7 +2386,7 @@ check_io_debug() ->
             %% one extra used fd that is not selected on
             ok
     end,
-    0 = NoDrvEvStructs,
+    0 = NoEnifSelStructs,
     ok.
 
 has_gethost() ->
@@ -2459,15 +2556,19 @@ sleep(Ms) when is_integer(Ms), Ms >= 0 ->
 
 
 start_node(Config) when is_list(Config) ->
+    start_node(proplists:get_value(testcase, Config));
+start_node(Name) ->
+    start_node(Name, "").
+start_node(NodeName, Args) ->
     Pa = filename:dirname(code:which(?MODULE)),
     Name = list_to_atom(atom_to_list(?MODULE)
                         ++ "-"
-                        ++ atom_to_list(proplists:get_value(testcase, Config))
+                        ++ atom_to_list(NodeName)
                         ++ "-"
                         ++ integer_to_list(erlang:system_time(second))
                         ++ "-"
                         ++ integer_to_list(erlang:unique_integer([positive]))),
-    test_server:start_node(Name, slave, [{args, "-pa "++Pa}]).
+    test_server:start_node(Name, slave, [{args, Args ++ " -pa "++Pa}]).
 
 stop_node(Node) ->
     test_server:stop_node(Node).
@@ -2500,3 +2601,35 @@ driver_alloc_size() ->
                       Sz0+Sz
               end, 0, CS)
     end.
+
+rpc(Config, Fun) ->
+    case proplists:get_value(node, Config) of
+        undefined ->
+            Fun();
+        Node ->
+            Self = self(),
+            Ref = make_ref(),
+            Pid = spawn(Node,
+                        fun() ->
+                                Result
+                                    = try Fun() of
+                                          Res -> Res
+                                      catch E:R ->
+                                              {'EXIT',E,R,erlang:get_stacktrace()}
+                                      end,
+                                Self ! {Ref, Result}
+                        end),
+            MRef = monitor(process, Pid),
+            receive
+                {'DOWN', MRef, _Type, _Object, Info} ->
+                    erlang:error({died, Pid, Info});
+                {Ref, {'EXIT',E,R,ST}} ->
+                    erlang:demonitor(MRef, [flush]),
+                    erlang:raise(E,R,ST);
+                {Ref, Ret} ->
+                    erlang:demonitor(MRef, [flush]),
+                    Ret;
+                Other ->
+                    ct:fail(Other)
+            end
+    end.
diff --git a/erts/emulator/test/driver_SUITE_data/chkio_drv.c b/erts/emulator/test/driver_SUITE_data/chkio_drv.c
index 8e5e81665c..d548c4b1dc 100644
--- a/erts/emulator/test/driver_SUITE_data/chkio_drv.c
+++ b/erts/emulator/test/driver_SUITE_data/chkio_drv.c
@@ -42,7 +42,6 @@
 #define CHKIO_STOP				0
 #define CHKIO_USE_FALLBACK_POLLSET		1
 #define CHKIO_BAD_FD_IN_POLLSET			2
-#define CHKIO_DRIVER_EVENT			3
 #define CHKIO_FD_CHANGE				4
 #define CHKIO_STEAL				5
 #define CHKIO_STEAL_AUX				6
@@ -67,15 +66,6 @@ typedef struct {
 } ChkioFallbackData;
 
 typedef struct {
-    int in_fd;
-    struct erl_drv_event_data in_data;
-    int in_ok;
-    int out_fd;
-    struct erl_drv_event_data out_data;
-    int out_ok;
-} ChkioDriverEvent;
-
-typedef struct {
     int fds[2];
     int same_fd;
 } ChkioFdChange;
@@ -86,14 +76,10 @@ typedef struct {
 
 typedef struct {
     int driver_select_fds[2];
-    int driver_event_fds[2];
-    struct erl_drv_event_data event_data[2];
 } ChkioSteal;
 
 typedef struct {
     int driver_select_fds[2];
-    int driver_event_fds[2];
-    struct erl_drv_event_data event_data[2];
 } ChkioStealAux;
 
 
@@ -141,7 +127,6 @@ static ErlDrvData chkio_drv_start(ErlDrvPort, char *);
 static void chkio_drv_stop(ErlDrvData);
 static void chkio_drv_ready_input(ErlDrvData, ErlDrvEvent);
 static void chkio_drv_ready_output(ErlDrvData, ErlDrvEvent);
-static void chkio_drv_ready_event(ErlDrvData, ErlDrvEvent, ErlDrvEventData);
 static ErlDrvSSizeT chkio_drv_control(ErlDrvData, unsigned int,
 				      char *, ErlDrvSizeT, char **, ErlDrvSizeT);
 static void chkio_drv_timeout(ErlDrvData);
@@ -164,7 +149,7 @@ static ErlDrvEntry chkio_drv_entry = {
     NULL, /* ready_async */
     NULL, /* flush */
     NULL, /* call */
-    chkio_drv_ready_event,
+    NULL, /* unused_event_callback */
 
     ERL_DRV_EXTENDED_MARKER,
     ERL_DRV_EXTENDED_MAJOR_VERSION,
@@ -243,25 +228,6 @@ stop_use_fallback_pollset(ChkioDrvData *cddp)
 }
 
 static void
-stop_driver_event(ChkioDrvData *cddp)
-{
-    if (cddp->test_data) {
-	ChkioDriverEvent *cdep = cddp->test_data;
-	cddp->test_data = NULL;
-
-	if (cdep->in_fd >= 0) {
-	    driver_event(cddp->port, (ErlDrvEvent) (ErlDrvSInt) cdep->in_fd, NULL);
-	    close(cdep->in_fd);
-	}
-	if (cdep->out_fd >= 0) {
-	    driver_event(cddp->port, (ErlDrvEvent) (ErlDrvSInt) cdep->out_fd, NULL);
-	    close(cdep->out_fd);
-	}
-	driver_free(cdep);	    
-    }
-}
-
-static void
 stop_fd_change(ChkioDrvData *cddp)
 {
     if (cddp->test_data) {
@@ -305,14 +271,6 @@ stop_steal(ChkioDrvData *cddp)
 			  (ErlDrvEvent) (ErlDrvSInt) csp->driver_select_fds[1],
 			  DO_WRITE,
 			  0);
-	if (csp->driver_event_fds[0] >= 0)
-	    driver_event(cddp->port,
-			 (ErlDrvEvent) (ErlDrvSInt) csp->driver_event_fds[0],
-			 NULL);
-	if (csp->driver_event_fds[1] >= 0)
-	    driver_event(cddp->port,
-			 (ErlDrvEvent) (ErlDrvSInt) csp->driver_event_fds[1],
-			 NULL);
 	driver_free(csp);
     }
 }
@@ -327,10 +285,6 @@ stop_steal_aux(ChkioDrvData *cddp)
 	    close(csap->driver_select_fds[0]);
 	if (csap->driver_select_fds[1] >= 0)
 	    close(csap->driver_select_fds[1]);
-	if (csap->driver_event_fds[0] >= 0)
-	    close(csap->driver_event_fds[0]);
-	if (csap->driver_event_fds[1] >= 0)
-	    close(csap->driver_event_fds[1]);
 	driver_free(csap);
     }
 }
@@ -354,10 +308,13 @@ static void free_smp_select(ChkioSmpSelect* pip, ErlDrvPort port)
 	abort();
     }
     case Selected:
-	driver_select(port, (ErlDrvEvent)(ErlDrvSInt)pip->read_fd, DO_READ, 0);
-	/*fall through*/ 
     case Opened:
-	close(pip->read_fd);
+        TRACEF(("%T: Close pipe [%d->%d]\n", driver_mk_port(port), pip->write_fd,
+                pip->read_fd));
+        if (pip->wasSelected)
+            driver_select(port, (ErlDrvEvent)(ErlDrvSInt)pip->read_fd, DO_READ|ERL_DRV_USE, 0);
+        else
+            close(pip->read_fd);
 	close(pip->write_fd);
 	pip->state = Closed;
 	break;
@@ -445,9 +402,6 @@ chkio_drv_stop(ErlDrvData drv_data) {
     case CHKIO_BAD_FD_IN_POLLSET:
 	stop_bad_fd_in_pollset(cddp);
 	break;
-    case CHKIO_DRIVER_EVENT:
-	stop_driver_event(cddp);
-	break;
     case CHKIO_FD_CHANGE:
 	stop_fd_change(cddp);
 	break;
@@ -557,6 +511,9 @@ chkio_drv_ready_input(ErlDrvData drv_data, ErlDrvEvent event)
 	    driver_failure_atom(cddp->port, "input_fd_not_found");
 	break;
     }
+    case CHKIO_FD_CHANGE:
+        /* This may be triggered when an fd is closed while being selected on. */
+        break;
     case CHKIO_STEAL:
 	break;
     case CHKIO_STEAL_AUX:
@@ -621,55 +578,6 @@ chkio_drv_ready_input(ErlDrvData drv_data, ErlDrvEvent event)
 }
 
 static void
-chkio_drv_ready_event(ErlDrvData drv_data,
-		      ErlDrvEvent event,
-		      ErlDrvEventData event_data)
-{
-#ifdef UNIX
-    ChkioDrvData *cddp = (ChkioDrvData *) drv_data;
-    switch (cddp->test) {
-    case CHKIO_DRIVER_EVENT: {
-#ifdef HAVE_POLL_H
-	ChkioDriverEvent *cdep = cddp->test_data;
-	int fd = (int) (ErlDrvSInt) event;
-	if (fd == cdep->in_fd) {
-	    if (event_data->events == POLLIN
-		&& event_data->revents == POLLIN) {
-		cdep->in_ok++;
-	    }
-	    else {
-		driver_failure_atom(cddp->port, "invalid_input_fd_events");
-	    }
-	    break;
-	}
-	if (fd == cdep->out_fd) {
-	    if (event_data->events == POLLOUT
-		&& event_data->revents == POLLOUT) {
-		cdep->out_ok++;
-	    }
-	    else {
-		driver_failure_atom(cddp->port, "invalid_output_fd_events");
-	    }
-	    break;
-	}
-#endif
-    }
-    case CHKIO_STEAL:
-#ifdef HAVE_POLL_H
-	break;
-#endif
-    case CHKIO_STEAL_AUX:
-#ifdef HAVE_POLL_H
-	break;
-#endif
-    default:
-	driver_failure_atom(cddp->port, "unexpected_ready_event");
-	break;
-    }
-#endif /* UNIX */
-}
-
-static void
 chkio_drv_timeout(ErlDrvData drv_data)
 {
 #ifdef UNIX
@@ -779,25 +687,6 @@ chkio_drv_control(ErlDrvData drv_data,
 	    res_len = -1;
 	    stop_bad_fd_in_pollset(cddp);
 	    break;
-	case CHKIO_DRIVER_EVENT: {
-	    ChkioDriverEvent *cdep = cddp->test_data;
-	    if (!cdep->in_ok || !cdep->out_ok) {
-		if (!cdep->in_ok)
-		    driver_failure_atom(cddp->port, "got_no_input_events");
-		if (!cdep->out_ok)
-		    driver_failure_atom(cddp->port, "got_no_output_events");
-	    }
-	    else {
-		char *c = driver_alloc(sizeof(char)*2*30);
-		if (!c)
-		    driver_failure_posix(cddp->port, ENOMEM);
-		*rbuf = c;
-		res_len = sprintf(c, "in=%d\nout=%d\n",
-				  cdep->in_ok, cdep->out_ok);
-	    }
-	    stop_driver_event(cddp);
-	    break;
-	}
 	case CHKIO_FD_CHANGE: {
 	    ChkioFdChange *cfcp = cddp->test_data;
 	    if (!cfcp->same_fd)
@@ -937,69 +826,6 @@ chkio_drv_control(ErlDrvData drv_data,
 	res_len = -1;
 	break;
     }
-    case CHKIO_DRIVER_EVENT: {
-#ifndef HAVE_POLL_H
-	res_str = "skip: Need the poll.h header for this test, but it doesn't exist";
-	res_len = -1;
-#else /* HAVE_POLL_H */
-	int in_fd = open("/dev/zero", O_RDONLY);
-	int out_fd = open("/dev/null", O_WRONLY);
-
-	if (in_fd < 0 || out_fd < 0) {
-	    if (in_fd >= 0)
-		close(in_fd);
-	    if (out_fd >= 0)
-		close(out_fd);
-	    driver_failure_posix(cddp->port, errno);
-	}
-	else {
-	    ChkioDriverEvent *cdep = driver_alloc(sizeof(ChkioDriverEvent));
-	    if (!cdep)
-		driver_failure_posix(cddp->port, ENOMEM);
-	    else {
-		int res;
-		cddp->test_data = cdep;
-
-		cdep->in_fd = in_fd;
-		cdep->in_data.events = POLLIN;
-		cdep->in_data.revents = 0;
-		cdep->in_ok = 0;
-
-		res = driver_event(cddp->port,
-				   (ErlDrvEvent) (ErlDrvSInt) in_fd,
-				   &cdep->in_data);
-		if (res < 0) {
-		    res_str = "skip: driver_event() not supported";
-		    res_len = -1;
-		    close(in_fd);
-		    close(out_fd);
-		    cdep->in_fd = -1;
-		    cdep->out_fd = -1;
-		}
-		else {
-		    res_str = "ok";
-		    res_len = -1;
-
-		    cdep->out_fd = out_fd;
-		    cdep->out_data.events = POLLOUT;
-		    cdep->out_data.revents = 0;
-		    cdep->out_ok = 0;
-
-		    res = driver_event(cddp->port,
-				       (ErlDrvEvent) (ErlDrvSInt) out_fd,
-				       &cdep->out_data);
-		    if (res < 0) {
-			close(out_fd);
-			cdep->out_fd = -1;
-			driver_failure_atom(cddp->port, "driver_event_failed");
-		    }
-		}
-
-	    }
-	}
-#endif /* HAVE_POLL_H */
-	break;
-    }
     case CHKIO_FD_CHANGE: {
 	ChkioFdChange *cfcp = driver_alloc(sizeof(ChkioFdChange));
 	if (!cfcp)
@@ -1028,58 +854,19 @@ chkio_drv_control(ErlDrvData drv_data,
 	    res_len = -1;
 	}
 	else {
-	    int driver_event_fds[2];
 	    int driver_select_fds[2];
 	    cddp->test_data = csp; 
 	    memcpy(c, buf, len);
 	    c[len] = '\0';
 	    if (sscanf(c,
-		       "fds:%d:%d:%d:%d",
+		       "fds:%d:%d",
 		       &driver_select_fds[0],
-		       &driver_select_fds[1],
-		       &driver_event_fds[0],
-		       &driver_event_fds[1]) != 4)
-		driver_failure_atom(cddp->port, "bad_input");
+		       &driver_select_fds[1]) != 2)
+                driver_failure_atom(cddp->port, "bad_input");
 	    else {
 		int res = 0;
-		if (driver_event_fds[0] < 0) { /* Have no working driver_event() ... */
-		    csp->driver_select_fds[0] = driver_select_fds[0]; /* In */
-		    csp->driver_select_fds[1] = driver_select_fds[1]; /* Out */
-		    csp->driver_event_fds[0] = -1;
-		    csp->driver_event_fds[1] = -1;
-		}
-		else { /* Have working driver_event() ... */
-#ifndef HAVE_POLL_H
-		    driver_failure_atom(cddp->port, "unexpected_result");
-		    res = -1;
-#else
-		    csp->driver_select_fds[0] = driver_select_fds[0]; /* In */
-		    csp->driver_event_fds[1] = driver_select_fds[1]; /* Out */
-		    csp->driver_event_fds[0] = driver_event_fds[0]; /* In */
-		    csp->driver_select_fds[1] = driver_event_fds[1]; /* Out */
-
-		    /* Steal with driver_event() */
-
-		    csp->event_data[0].events = POLLIN;
-		    csp->event_data[0].revents = 0;
-		    res = driver_event(cddp->port,
-				       (ErlDrvEvent) (ErlDrvSInt) csp->driver_event_fds[0],
-				       &csp->event_data[0]);
-		    if (res < 0)
-			driver_failure_atom(cddp->port,
-					    "driver_event_failed_to_steal");
-		    if (res >= 0) {
-			csp->event_data[1].events = POLLOUT;
-			csp->event_data[1].revents = 0;
-			res = driver_event(cddp->port,
-					   (ErlDrvEvent) (ErlDrvSInt) csp->driver_event_fds[1],
-					   &csp->event_data[1]);
-			if (res < 0)
-			    driver_failure_atom(cddp->port,
-						"driver_event_failed_to_steal");
-		    }
-#endif
-		}
+                csp->driver_select_fds[0] = driver_select_fds[0]; /* In */
+                csp->driver_select_fds[1] = driver_select_fds[1]; /* Out */
 
 		/* Steal with driver_select() */
 		if (res >= 0) {
@@ -1109,37 +896,17 @@ chkio_drv_control(ErlDrvData drv_data,
 	break;
     }
     case CHKIO_STEAL_AUX: {
-	int read_fds[2];
-	int write_fds[2];
+	int read_fd;
+	int write_fd;
 
-	read_fds[0] = open("/dev/zero", O_RDONLY);
-	write_fds[0] = open("/dev/null", O_WRONLY);
-
-#ifdef HAVE_POLL_H
-	read_fds[1] = open("/dev/zero", O_RDONLY);
-	write_fds[1] = open("/dev/null", O_WRONLY);
-#else
-	read_fds[1] = -1;
-	write_fds[1] = -1;
-#endif
+	read_fd = open("/dev/zero", O_RDONLY);
+	write_fd = open("/dev/null", O_WRONLY);
 	
-	if (read_fds[0] < 0
-	    || write_fds[0] < 0
-#ifdef HAVE_POLL_H
-	    || read_fds[1] < 0 
-	    || write_fds[1] < 0
-#endif
-	    ) {
-	    if (read_fds[0] < 0)
-		close(read_fds[0]);
-	    if (write_fds[0] < 0)
-		close(write_fds[0]);
-#ifdef HAVE_POLL_H
-	    if (read_fds[1] < 0)
-		close(read_fds[1]);
-	    if (write_fds[1] < 0)
-		close(write_fds[1]);
-#endif
+	if (read_fd < 0 || write_fd < 0) {
+	    if (read_fd < 0)
+		close(read_fd);
+	    if (write_fd < 0)
+		close(write_fd);
 	    driver_failure_posix(cddp->port, errno);
 	}
 	else {
@@ -1153,11 +920,8 @@ chkio_drv_control(ErlDrvData drv_data,
 		int res;
 		cddp->test_data = csap;
 
-		csap->driver_select_fds[0] = read_fds[0];
-		csap->driver_select_fds[1] = write_fds[0];
-
-		csap->driver_event_fds[0] = read_fds[1];
-		csap->driver_event_fds[1] = write_fds[1];
+		csap->driver_select_fds[0] = read_fd;
+		csap->driver_select_fds[1] = write_fd;
 
 		res = driver_select(cddp->port,
 				    (ErlDrvEvent) (ErlDrvSInt) csap->driver_select_fds[0],
@@ -1173,32 +937,6 @@ chkio_drv_control(ErlDrvData drv_data,
 		    if (res < 0)
 			driver_failure_atom(cddp->port, "driver_select_failed");
 		}
-#ifdef HAVE_POLL_H
-		if (res >= 0) {
-		    csap->event_data[0].events = POLLIN;
-		    csap->event_data[0].revents = 0;
-		    res = driver_event(cddp->port,
-				       (ErlDrvEvent) (ErlDrvSInt) csap->driver_event_fds[0],
-				       &csap->event_data[0]);
-		    if (res < 0) {
-			close(csap->driver_event_fds[0]);
-			csap->driver_event_fds[0] = -1;
-			close(csap->driver_event_fds[1]);
-			csap->driver_event_fds[1] = -1;
-			res = 0;
-		    }
-		    else {
-			csap->event_data[1].events = POLLOUT;
-			csap->event_data[1].revents = 0;
-			res = driver_event(cddp->port,
-					   (ErlDrvEvent) (ErlDrvSInt) csap->driver_event_fds[1],
-					   &csap->event_data[1]);
-			if (res < 0)
-			    driver_failure_atom(cddp->port,
-						"driver_event_failed");
-		    }
-		}
-#endif
 		if (res < 0) {
 		    res_str = "error";
 		    res_len = -1;
@@ -1213,11 +951,9 @@ chkio_drv_control(ErlDrvData drv_data,
 		    else {
 			*rbuf = c;
 			res_len = sprintf(c,
-					  "fds:%d:%d:%d:%d",
+					  "fds:%d:%d",
 					  csap->driver_select_fds[0],
-					  csap->driver_select_fds[1],
-					  csap->driver_event_fds[0],
-					  csap->driver_event_fds[1]);
+					  csap->driver_select_fds[1]);
 		    }
 		}
 	    }
@@ -1257,7 +993,7 @@ chkio_drv_control(ErlDrvData drv_data,
 		}
 		TRACEF(("%T: Created pipe [%d->%d]\n", cddp->id, fds[1], fds[0]));
 		pip->read_fd = fds[0];
-		pip->write_fd = fds[1];	       
+		pip->write_fd = fds[1];
 		pip->state = Opened;
 		pip->wasSelected = 0;
 		pip->next_write = pip->next_read = rand_r(&pip->rand_state) % 1024;
@@ -1267,7 +1003,8 @@ chkio_drv_control(ErlDrvData drv_data,
 	    }/*fall through*/
 	    case Opened: {
 		if (op & 1) {
-		    TRACEF(("%T: Write %d to opened pipe [%d->%d]\n", cddp->id, pip->next_write, pip->write_fd, pip->read_fd));
+		    TRACEF(("%T: Write %d to opened pipe [%d->%d]\n", cddp->id,
+                            pip->next_write, pip->write_fd, pip->read_fd));
 		    if (write(pip->write_fd, &pip->next_write, sizeof(int)) != sizeof(int)) {
 			fprintf(stderr, "Failed to write to pipe fd=%d, errno=%d\n", pip->write_fd, errno);
 			abort();
@@ -1276,8 +1013,12 @@ chkio_drv_control(ErlDrvData drv_data,
 		}
 		op >>= 1;
 		if (pip->wasSelected && (op & 1)) {
-		    TRACEF(("%T: Close pipe [%d->%d]\n", cddp->id, pip->write_fd, pip->read_fd));
-		    if (close(pip->read_fd) || close(pip->write_fd)) {
+		    TRACEF(("%T: Close pipe [%d->%d]\n", cddp->id, pip->write_fd,
+                            pip->read_fd));
+                    drv_use_singleton.fd_stop_select = -2; /* disable stop_select asserts */
+		    if (driver_select(cddp->port, (ErlDrvEvent)(ErlDrvSInt)pip->read_fd,
+                                      DO_READ|ERL_DRV_USE, 0)
+                        || close(pip->write_fd)) {
 			fprintf(stderr, "Failed to close pipe, errno=%d\n", errno);
 			abort();
 		    }
@@ -1285,8 +1026,10 @@ chkio_drv_control(ErlDrvData drv_data,
 		    break;
 		}
 		else {
-		    TRACEF(("%T: Select on pipe [%d->%d]\n", cddp->id, pip->write_fd, pip->read_fd));
-		    if (driver_select(cddp->port, (ErlDrvEvent)(ErlDrvSInt)pip->read_fd, DO_READ, 1)) {
+		    TRACEF(("%T: Select on pipe [%d->%d]\n", cddp->id,
+                            pip->write_fd, pip->read_fd));
+		    if (driver_select(cddp->port, (ErlDrvEvent)(ErlDrvSInt)pip->read_fd,
+                                      DO_READ|ERL_DRV_USE, 1)) {
 			fprintf(stderr, "driver_select failed for fd=%d\n", pip->read_fd);
 			abort();
 		    }
@@ -1294,13 +1037,13 @@ chkio_drv_control(ErlDrvData drv_data,
 		    pip->wasSelected = 1;
 		    op >>= 1;
 		    if (pip->next_write != pip->next_read) { /* pipe not empty */
-			if (op & 1) {  
+			if (op & 1) {
 			    pip->state = Waiting; /* Wait for reader */
 			    break;
 			}
 			op >>= 1;
 		    }
-		}  
+		}
 	    }/*fall through*/
 	    case Selected:
 		if (op & 1) {
@@ -1329,7 +1072,7 @@ chkio_drv_control(ErlDrvData drv_data,
 			fprintf(stderr, "Failed to write to pipe fd=%d, errno=%d\n", pip->write_fd, errno);
 			abort();
 		    }
-		    pip->next_write++;		    
+		    pip->next_write++;
 		}
 		break;
 	    case Waiting:
@@ -1583,7 +1326,12 @@ static void chkio_drv_stop_select(ErlDrvEvent e, void* null)
     if (!(drv_use_singleton.fd_stop_select < 0)) {
 	assert_print("fd_stop_select<0", __LINE__); abort(); 
     }
-    drv_use_singleton.fd_stop_select = (int)(long)e;
+    /* fd_stop_select counting is disabled if this is set to -2 */
+    if (drv_use_singleton.fd_stop_select == -2) {
+        TRACEF(("closing %d\n", (int)(long)e));
+        close((int)(long)e);
+    } else
+        drv_use_singleton.fd_stop_select = (int)(long)e;
     /* Can't call chkio_drv_use directly here. That could even be recursive.
      * Next timeout will detect it instead.
      */
diff --git a/erts/emulator/test/driver_SUITE_data/ioq_exit_drv.c b/erts/emulator/test/driver_SUITE_data/ioq_exit_drv.c
index d87c2bec93..fa58e9d5ec 100644
--- a/erts/emulator/test/driver_SUITE_data/ioq_exit_drv.c
+++ b/erts/emulator/test/driver_SUITE_data/ioq_exit_drv.c
@@ -25,8 +25,7 @@
  *		- ready_input(),
  *		- ready_output(),
  *		- timeout(),
- *		- driver_async() -> read_async(), and
- *		- event()
+ *		- driver_async() -> read_async()
  */
 
 #ifndef UNIX
@@ -65,11 +64,9 @@ typedef enum {
     IOQ_EXIT_READY_OUTPUT = 2,
     IOQ_EXIT_TIMEOUT = 3,
     IOQ_EXIT_READY_ASYNC = 4,
-    IOQ_EXIT_EVENT = 5,
     IOQ_EXIT_READY_INPUT_ASYNC = 6,
     IOQ_EXIT_READY_OUTPUT_ASYNC = 7,
     IOQ_EXIT_TIMEOUT_ASYNC = 8,
-    IOQ_EXIT_EVENT_ASYNC = 9
 } IOQExitTest;
 
 typedef struct {
@@ -80,9 +77,6 @@ typedef struct {
     int outstanding_async_task;
     long async_task;
     ErlDrvPDL pdl;
-#ifdef HAVE_POLL_H
-    struct erl_drv_event_data event_data;
-#endif
 } IOQExitDrvData;
 
 #define EV2FD(EV) ((int) ((long) (EV)))
@@ -97,8 +91,6 @@ static ErlDrvSSizeT control(ErlDrvData, unsigned int,
 static void timeout(ErlDrvData drv_data);
 static void ready_async(ErlDrvData drv_data, ErlDrvThreadData thread_data);
 static void flush(ErlDrvData drv_data);
-static void event(ErlDrvData drv_data, ErlDrvEvent event,
-		  ErlDrvEventData event_data);
 static void async_invoke(void*);
 static void do_driver_async(IOQExitDrvData *);
 
@@ -118,7 +110,7 @@ static ErlDrvEntry ioq_exit_drv_entry = {
     ready_async,
     flush,
     NULL /* call */,
-    event,
+    NULL /* unused_event_callback*/,
     ERL_DRV_EXTENDED_MARKER,
     ERL_DRV_EXTENDED_MAJOR_VERSION,
     ERL_DRV_EXTENDED_MINOR_VERSION,
@@ -149,10 +141,6 @@ start(ErlDrvPort port, char *command)
     ddp->outstanding_async_task = 0;
     ddp->async_task = -1;
     ddp->pdl = driver_pdl_create(port);
-#ifdef HAVE_POLL_H
-    ddp->event_data.events = (short) 0;
-    ddp->event_data.revents = (short) 0;
-#endif
 
     return (ErlDrvData) ddp;
 }
@@ -192,27 +180,6 @@ static ErlDrvSSizeT control(ErlDrvData drv_data,
 #else
 	goto done;
 #endif
-    case IOQ_EXIT_EVENT:
-    case IOQ_EXIT_EVENT_ASYNC:
-#ifdef UNIX
-#ifdef HAVE_POLL_H
-	ddp->ofd = open("/dev/null", O_WRONLY);
-	if (ddp->ofd < 0) {
-	    driver_failure_posix(ddp->port, errno);
-	    return 0;
-	}
-	else if (driver_event(ddp->port, FD2EV(ddp->ofd), NULL) != 0) {
-	    res_str = "skip: driver_event() not supported";
-	    goto done;
-	}
-#else
-	res_str = "skip: No poll.h found which is needed for this test";
-	goto done;
-#endif
-	break;
-#else /* UNIX */
-	goto done;
-#endif
     case IOQ_EXIT_TIMEOUT:
     case IOQ_EXIT_TIMEOUT_ASYNC:
 	break;
@@ -266,13 +233,6 @@ static void stop(ErlDrvData drv_data)
 		close(ddp->ofd);
 	    }
 	    break;
-	case IOQ_EXIT_EVENT:
-	case IOQ_EXIT_EVENT_ASYNC:
-	    if (ddp->ofd >= 0) {
-		driver_event(ddp->port, FD2EV(ddp->ofd), NULL);
-		close(ddp->ofd);
-	    }
-	    break;
 #endif
 	case IOQ_EXIT_TIMEOUT:
 	case IOQ_EXIT_TIMEOUT_ASYNC:
@@ -302,13 +262,6 @@ static void flush(ErlDrvData drv_data)
     case IOQ_EXIT_READY_OUTPUT_ASYNC:
 	driver_select(ddp->port, FD2EV(ddp->ofd), DO_WRITE, 1);
 	break;
-    case IOQ_EXIT_EVENT:
-    case IOQ_EXIT_EVENT_ASYNC:
-#ifdef HAVE_POLL_H
-	ddp->event_data.events |= POLLOUT;
-	driver_event(ddp->port, FD2EV(ddp->ofd), &ddp->event_data);
-#endif
-	break;
 #endif
     case IOQ_EXIT_TIMEOUT:
     case IOQ_EXIT_TIMEOUT_ASYNC:
@@ -395,30 +348,6 @@ static void ready_async(ErlDrvData drv_data, ErlDrvThreadData thread_data)
     }
 }
 
-static void event(ErlDrvData drv_data,
-		  ErlDrvEvent event,
-		  ErlDrvEventData event_data)
-{
-    IOQExitDrvData *ddp = (IOQExitDrvData *) drv_data;
-
-    PRINTF(("event(%p, %d, %p) called\r\n", drv_data, EV2FD(event), event_data));
-
-#if defined(UNIX) && defined(HAVE_POLL_H)
-    if (ddp->ofd == EV2FD(event)) {
-	driver_event(ddp->port, FD2EV(ddp->ofd), NULL);
-	close(ddp->ofd);
-	ddp->ofd = -1;
-	if (ddp->test == IOQ_EXIT_EVENT_ASYNC)
-	    do_driver_async(ddp);
-	else {
-	    driver_pdl_lock(ddp->pdl);
-	    driver_deq(ddp->port, 1);
-	    driver_pdl_unlock(ddp->pdl);
-	}
-    }
-#endif
-}
-
 static void async_invoke(void *arg)
 {
     PRINTF(("async_invoke(%p) called\r\n", arg));
diff --git a/erts/emulator/test/driver_SUITE_data/missing_callback_drv.c b/erts/emulator/test/driver_SUITE_data/missing_callback_drv.c
index e7480d2e00..14838f0377 100644
--- a/erts/emulator/test/driver_SUITE_data/missing_callback_drv.c
+++ b/erts/emulator/test/driver_SUITE_data/missing_callback_drv.c
@@ -41,10 +41,6 @@
 typedef struct {
     int ofd;
     int ifd;
-    int efd;
-#ifdef HAVE_POLL_H
-    struct erl_drv_event_data edata;
-#endif
 } mcd_data_t;
 
 static ErlDrvData start(ErlDrvPort port, char *command);
@@ -90,7 +86,6 @@ start(ErlDrvPort port, char *command)
 
     mcd->ofd = -1;
     mcd->ifd = -1;
-    mcd->efd = -1;
 
 #ifdef UNIX
 
@@ -105,15 +100,6 @@ start(ErlDrvPort port, char *command)
 	goto error;
     if (driver_select(port, (ErlDrvEvent) (long) mcd->ifd, DO_READ, 1) != 0)
 	goto error;
-
-#ifdef HAVE_POLL_H
-    mcd->efd = open("/dev/null", O_WRONLY);
-    if (mcd->efd < 0)
-	goto error;
-    mcd->edata.events = POLLOUT;
-    mcd->edata.revents = 0;
-    driver_event(port, (ErlDrvEvent) (long) mcd->efd, &mcd->edata);
-#endif
 #endif
 
     driver_set_timer(port, 0);
@@ -135,10 +121,6 @@ stop(ErlDrvData data)
 	    close(mcd->ofd);
 	if (mcd->ifd >= 0)
 	    close(mcd->ifd);
-#ifdef HAVE_POLL_H
-	if (mcd->efd >= 0)
-	    close(mcd->efd);
-#endif
 #endif
 	driver_free(mcd);
     }
diff --git a/erts/emulator/test/lttng_SUITE.erl b/erts/emulator/test/lttng_SUITE.erl
index a012fa1da2..19c3844c40 100644
--- a/erts/emulator/test/lttng_SUITE.erl
+++ b/erts/emulator/test/lttng_SUITE.erl
@@ -81,7 +81,6 @@ end_per_testcase(Case, _Config) ->
 
 %% Not tested yet
 %%   org_erlang_otp:driver_process_exit
-%%   org_erlang_otp:driver_event
 
 %% tracepoints
 %%
@@ -100,7 +99,6 @@ end_per_testcase(Case, _Config) ->
 %%   org_erlang_otp:driver_flush
 %%   org_erlang_otp:driver_stop_select
 %%   org_erlang_otp:driver_timeout
-%%   org_erlang_otp:driver_event
 %%   org_erlang_otp:driver_ready_output
 %%   org_erlang_otp:driver_ready_input
 %%   org_erlang_otp:driver_output
@@ -431,7 +429,6 @@ txt() ->
       "%%   org_erlang_otp:driver_flush\n"
       "%%   org_erlang_otp:driver_stop_select\n"
       "%%   org_erlang_otp:driver_timeout\n"
-      "%%   org_erlang_otp:driver_event\n"
       "%%   org_erlang_otp:driver_ready_output\n"
       "%%   org_erlang_otp:driver_ready_input\n"
       "%%   org_erlang_otp:driver_output\n"
diff --git a/erts/emulator/test/nif_SUITE.erl b/erts/emulator/test/nif_SUITE.erl
index 223bd7d586..bec2291867 100644
--- a/erts/emulator/test/nif_SUITE.erl
+++ b/erts/emulator/test/nif_SUITE.erl
@@ -25,13 +25,14 @@
 %%-define(CHECK(Exp,Got), Exp = Got).
 
 -include_lib("common_test/include/ct.hrl").
+-include_lib("stdlib/include/assert.hrl").
 
 -export([all/0, suite/0, groups/0,
          init_per_group/2, end_per_group/2,
 	 init_per_testcase/2, end_per_testcase/2,
          basic/1, reload_error/1, upgrade/1, heap_frag/1,
          t_on_load/1,
-         select/1,
+         select/1, select_steal/1,
          monitor_process_a/1,
          monitor_process_b/1,
          monitor_process_c/1,
@@ -42,9 +43,9 @@
 	 types/1, many_args/1, binaries/1, get_string/1, get_atom/1,
 	 maps/1,
 	 api_macros/1,
-	 from_array/1, iolist_as_binary/1, resource/1, resource_binary/1, 
+	 from_array/1, iolist_as_binary/1, resource/1, resource_binary/1,
 	 resource_takeover/1,
-	 threading/1, send/1, send2/1, send3/1, send_threaded/1, neg/1, 
+	 threading/1, send/1, send2/1, send3/1, send_threaded/1, neg/1,
 	 is_checks/1,
 	 get_length/1, make_atom/1, make_string/1, reverse_list_test/1,
 	 otp_9828/1,
@@ -79,7 +80,7 @@ all() ->
     [{group, G} || G <- api_groups()]
         ++
     [reload_error, heap_frag, types, many_args,
-     select,
+     select, select_steal,
      {group, monitor},
      monitor_frenzy,
      hipe,
@@ -144,7 +145,8 @@ init_per_testcase(nif_whereis_threaded, Config) ->
         true -> Config;
         false -> {skip, "No thread support"}
     end;
-init_per_testcase(select, Config) ->
+init_per_testcase(Select, Config) when Select =:= select;
+                                       Select =:= select_steal ->
     case os:type() of
         {win32,_} ->
             {skip, "Test not yet implemented for windows"};
@@ -152,6 +154,9 @@ init_per_testcase(select, Config) ->
             Config
     end;
 init_per_testcase(_Case, Config) ->
+    %% Clear any resource dtor data before test starts in case another tc
+    %% left it in a bad state
+    catch last_resource_dtor_call(),
     Config.
 
 end_per_testcase(t_on_load, _Config) ->
@@ -590,7 +595,71 @@ select_3(_Config) ->
     {_,_,2} = last_resource_dtor_call(),
     ok.
 
-check_stop_ret(?ERL_NIF_SELECT_STOP_CALLED) -> ok;    
+%% @doc The stealing child process for the select_steal test. Duplicates given
+%% W/RFds and runs select on them to steal
+select_steal_child_process(Parent, RFd) ->
+    %% Duplicate the resource with the same FD
+    {R2Fd, _R2Ptr} = dupe_resource_nif(RFd),
+    Ref2 = make_ref(),
+
+    %% Try to select from the child pid (steal from parent)
+    ?assertEqual(0, select_nif(R2Fd, ?ERL_NIF_SELECT_READ, R2Fd, null, Ref2)),
+    ?assertEqual([], flush(0)),
+    ?assertEqual(eagain, read_nif(R2Fd, 1)),
+
+    %% Check that now events arrive to this temporary process
+    Parent ! {self(), stage1}, % signal parent to send the <<"stolen1">>
+
+    %% Receive <<"stolen1">> via enif_select
+    ?assertEqual(0, select_nif(R2Fd, ?ERL_NIF_SELECT_READ, R2Fd, null, Ref2)),
+    ?assertMatch([{select, R2Fd, Ref2, ready_input}], flush()),
+    ?assertEqual(<<"stolen1">>, read_nif(R2Fd, 7)),
+
+    clear_select_nif(R2Fd),
+
+    % do not do this here - stop_selecting(R2Fd, R2Rsrc, Ref2),
+    Parent ! {self(), done}.
+
+%% @doc Similar to select/1 test, make a double ended pipe. Then try to steal
+%% the socket, see what happens.
+select_steal(Config) when is_list(Config) ->
+    ensure_lib_loaded(Config),
+
+    Ref = make_ref(),
+    {{RFd, RPtr}, {WFd, WPtr}} = pipe_nif(),
+
+    %% Bind the socket to current pid in enif_select
+    ?assertEqual(0, select_nif(RFd, ?ERL_NIF_SELECT_READ, RFd, null, Ref)),
+    ?assertEqual([], flush(0)),
+
+    %% Spawn a process and do some stealing
+    Parent = self(),
+    Pid = spawn_link(fun() -> select_steal_child_process(Parent, RFd) end),
+
+    %% Signal from the child to send the first message
+    {Pid, stage1} = receive_any(),
+    ?assertEqual(ok, write_nif(WFd, <<"stolen1">>)),
+
+    ?assertMatch([{Pid, done}], flush(1)),  % synchronize with the child
+
+    %% Try to select from the parent pid (steal back)
+    ?assertEqual(0, select_nif(RFd, ?ERL_NIF_SELECT_READ, RFd, Pid, Ref)),
+
+    %% Ensure that no data is hanging and close.
+    %% Rfd is stolen at this point.
+    check_stop_ret(select_nif(WFd, ?ERL_NIF_SELECT_STOP, WFd, null, Ref)),
+    ?assertMatch([{fd_resource_stop, WPtr, _}], flush()),
+    {1, {WPtr, 1}} = last_fd_stop_call(),
+
+    check_stop_ret(select_nif(RFd, ?ERL_NIF_SELECT_STOP, RFd, null, Ref)),
+    ?assertMatch([{fd_resource_stop, RPtr, _}], flush()),
+    {1, {RPtr, 1}} = last_fd_stop_call(),
+
+    ?assert(is_closed_nif(WFd)),
+
+    ok.
+
+check_stop_ret(?ERL_NIF_SELECT_STOP_CALLED) -> ok;
 check_stop_ret(?ERL_NIF_SELECT_STOP_SCHEDULED) -> ok.
 
 write_full(W, C) ->
@@ -3193,10 +3262,12 @@ binary_to_term_nif(_, _, _) -> ?nif_stub.
 port_command_nif(_, _) -> ?nif_stub.
 format_term_nif(_,_) -> ?nif_stub.
 select_nif(_,_,_,_,_) -> ?nif_stub.
+dupe_resource_nif(_) -> ?nif_stub.
 pipe_nif() -> ?nif_stub.
 write_nif(_,_) -> ?nif_stub.
 read_nif(_,_) -> ?nif_stub.
 is_closed_nif(_) -> ?nif_stub.
+clear_select_nif(_) -> ?nif_stub.
 last_fd_stop_call() -> ?nif_stub.
 alloc_monitor_resource_nif() -> ?nif_stub.
 monitor_process_nif(_,_,_,_) -> ?nif_stub.
diff --git a/erts/emulator/test/nif_SUITE_data/nif_SUITE.c b/erts/emulator/test/nif_SUITE_data/nif_SUITE.c
index b47d013bd2..79560a38aa 100644
--- a/erts/emulator/test/nif_SUITE_data/nif_SUITE.c
+++ b/erts/emulator/test/nif_SUITE_data/nif_SUITE.c
@@ -2448,6 +2448,13 @@ static int get_fd(ErlNifEnv* env, ERL_NIF_TERM term, struct fd_resource** rsrc)
     return 1;
 }
 
+/* Returns: badarg
+ *    Or an enif_select result, which is a combination of bits:
+ *    ERL_NIF_SELECT_STOP_CALLED = 1
+ *    ERL_NIF_SELECT_STOP_SCHEDULED = 2
+ *    ERL_NIF_SELECT_INVALID_EVENT = 4
+ *    ERL_NIF_SELECT_FAILED = 8
+ */
 static ERL_NIF_TERM select_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
 {
     struct fd_resource* fdr;
@@ -2479,6 +2486,9 @@ static ERL_NIF_TERM select_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv
 }
 
 #ifndef __WIN32__
+/*
+ * Create a read-write pipe with two fds (to read and to write)
+ */
 static ERL_NIF_TERM pipe_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
 {
     struct fd_resource* read_rsrc;
@@ -2514,6 +2524,30 @@ static ERL_NIF_TERM pipe_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]
                enif_make_tuple2(env, write_fd, make_pointer(env, write_rsrc)));
 }
 
+/*
+ * Create (dupe) of a resource with the same fd, to test stealing
+ */
+static ERL_NIF_TERM dupe_resource_nif(ErlNifEnv* env, int argc,
+                                      const ERL_NIF_TERM argv[]) {
+    struct fd_resource* orig_rsrc;
+
+    if (!get_fd(env, argv[0], &orig_rsrc)) {
+        return enif_make_badarg(env);
+    } else {
+        struct fd_resource* new_rsrc;
+        ERL_NIF_TERM new_fd;
+
+        new_rsrc = enif_alloc_resource(fd_resource_type,
+                                       sizeof(struct fd_resource));
+        new_rsrc->fd = orig_rsrc->fd;
+        new_rsrc->was_selected = 0;
+        new_fd = enif_make_resource(env, new_rsrc);
+        enif_release_resource(new_rsrc);
+
+        return enif_make_tuple2(env, new_fd, make_pointer(env, new_rsrc));
+    }
+}
+
 static ERL_NIF_TERM write_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
 {
     struct fd_resource* fdr;
@@ -2589,6 +2623,20 @@ static ERL_NIF_TERM is_closed_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM a
 
     return fdr->fd < 0 ? atom_true : atom_false;
 }
+
+static ERL_NIF_TERM clear_select_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
+{
+    struct fd_resource* fdr = NULL;
+
+    if (!get_fd(env, argv[0], &fdr))
+        return enif_make_badarg(env);
+
+    fdr->fd = -1;
+    fdr->was_selected = 0;
+
+    return atom_ok;
+}
+
 #endif /* !__WIN32__ */
 
 
@@ -3476,8 +3524,10 @@ static ErlNifFunc nif_funcs[] =
 #ifndef __WIN32__
     {"pipe_nif", 0, pipe_nif},
     {"write_nif", 2, write_nif},
+    {"dupe_resource_nif", 1, dupe_resource_nif},
     {"read_nif", 2, read_nif},
     {"is_closed_nif", 1, is_closed_nif},
+    {"clear_select_nif", 1, clear_select_nif},
 #endif
     {"last_fd_stop_call", 0, last_fd_stop_call},
     {"alloc_monitor_resource_nif", 0, alloc_monitor_resource_nif},
diff --git a/erts/emulator/test/scheduler_SUITE.erl b/erts/emulator/test/scheduler_SUITE.erl
index 12e26671c2..7afb82a1b8 100644
--- a/erts/emulator/test/scheduler_SUITE.erl
+++ b/erts/emulator/test/scheduler_SUITE.erl
@@ -57,6 +57,7 @@
 	 scheduler_suspend_basic/1,
 	 scheduler_suspend/1,
 	 dirty_scheduler_threads/1,
+         poll_threads/1,
 	 reader_groups/1]).
 
 suite() ->
@@ -72,6 +73,7 @@ all() ->
      {group, scheduler_bind}, scheduler_threads,
      scheduler_suspend_basic, scheduler_suspend,
      dirty_scheduler_threads,
+     poll_threads,
      reader_groups].
 
 groups() -> 
@@ -1446,6 +1448,79 @@ sst5_loop(N) ->
     erlang:system_flag(multi_scheduling, unblock_normal),
     sst5_loop(N-1).
 
+poll_threads(Config) when is_list(Config) ->
+    {Conc, PollType, KP} = get_ioconfig(Config),
+    {Sched, SchedOnln, _} = get_sstate(Config, ""),
+
+    [1, 1] = get_ionum(Config,"+IOt 2 +IOp 2"),
+    [1, 1, 1, 1, 1] = get_ionum(Config,"+IOt 5 +IOp 5"),
+
+    [1, 1] = get_ionum(Config, "+S 2 +IOPt 100 +IOPp 100"),
+
+    if
+        Conc ->
+            [5] = get_ionum(Config,"+IOt 5 +IOp 1"),
+            [3, 2] = get_ionum(Config,"+IOt 5 +IOp 2"),
+            [2, 2, 2, 2, 2] = get_ionum(Config,"+IOt 10 +IOPp 50"),
+
+            [2] = get_ionum(Config, "+S 2 +IOPt 100"),
+            [4] = get_ionum(Config, "+S 4 +IOPt 100"),
+            [4] = get_ionum(Config, "+S 4:2 +IOPt 100"),
+            [4, 4] = get_ionum(Config, "+S 8 +IOPt 100 +IOPp 25"),
+
+            fail = get_ionum(Config, "+IOt 1 +IOp 2"),
+
+            ok;
+        not Conc ->
+            [1, 1, 1, 1, 1] = get_ionum(Config,"+IOt 5 +IOp 1"),
+            [1, 1, 1, 1, 1] = get_ionum(Config,"+IOt 5 +IOp 2"),
+            [1, 1, 1, 1, 1, 1, 1, 1, 1, 1] = get_ionum(Config,"+IOt 10 +IOPp 50"),
+
+            [1, 1] = get_ionum(Config, "+S 2 +IOPt 100"),
+            [1, 1, 1, 1] = get_ionum(Config, "+S 4 +IOPt 100"),
+            [1, 1, 1, 1] = get_ionum(Config, "+S 4:2 +IOPt 100"),
+            [1, 1, 1, 1, 1, 1, 1, 1] = get_ionum(Config, "+S 8 +IOPt 100 +IOPp 25"),
+
+            [1] = get_ionum(Config, "+IOt 1 +IOp 2"),
+
+            ok
+    end,
+
+    fail = get_ionum(Config, "+IOt 1 +IOPp 101"),
+    fail = get_ionum(Config, "+IOt 0"),
+    fail = get_ionum(Config, "+IOPt 101"),
+
+    ok.
+
+get_ioconfig(Config) ->
+    [PS | _] = get_iostate(Config, ""),
+    {proplists:get_value(concurrent_updates, PS),
+     proplists:get_value(primary, PS),
+     proplists:get_value(kernel_poll, PS)}.
+
+get_ionum(Config, Cmd) ->
+    case get_iostate(Config, Cmd) of
+        fail -> fail;
+        PSs ->
+            lists:reverse(
+              lists:sort(
+                [proplists:get_value(poll_threads, PS) || PS <- PSs]))
+    end.
+
+get_iostate(Config, Cmd)->
+    case start_node(Config, Cmd) of
+        {ok, Node} ->
+            [IOStates] = mcall(Node,[fun () ->
+                                             erlang:system_info(check_io)
+                                     end]),
+            IO = [IOState || IOState <- IOStates,
+                             proplists:get_value(fallback, IOState) == false],
+            stop_node(Node),
+            IO;
+        {error,timeout} ->
+            fail
+    end.
+
 reader_groups(Config) when is_list(Config) ->
     %% White box testing. These results are correct, but other results
     %% could be too...
@@ -1770,18 +1845,24 @@ mcall(Node, Funs) ->
     Parent = self(),
     Refs = lists:map(fun (Fun) ->
                              Ref = make_ref(),
-                             spawn_link(Node,
-                                        fun () ->
-                                                Res = Fun(),
-                                                unlink(Parent),
-                                                Parent ! {Ref, Res}
-                                        end),
-                             Ref
+                             Pid = spawn(Node,
+                                         fun () ->
+                                                 Res = Fun(),
+                                                 unlink(Parent),
+                                                 Parent ! {Ref, Res}
+                                         end),
+                             MRef = erlang:monitor(process, Pid),
+                             {Ref, MRef}
                      end, Funs),
-    lists:map(fun (Ref) ->
+    lists:map(fun ({Ref, MRef}) ->
                       receive
                           {Ref, Res} ->
-                              Res
+                              receive
+                                  {'DOWN',MRef,_,_,_} ->
+                                      Res
+                              end;
+                          {'DOWN',MRef,_,_,Reason} ->
+                              Reason
                       end
               end, Refs).
 
diff --git a/erts/emulator/test/statistics_SUITE.erl b/erts/emulator/test/statistics_SUITE.erl
index 7a396d273c..029a6de897 100644
--- a/erts/emulator/test/statistics_SUITE.erl
+++ b/erts/emulator/test/statistics_SUITE.erl
@@ -674,6 +674,16 @@ msacc_test(TmpFile) ->
     ets:insert(Tid, {1, hello}),
     ets:delete(Tid),
 
+    %% Check some IO
+    {ok, L} = gen_tcp:listen(0, [{active, true},{reuseaddr,true}]),
+    {ok, Port} = inet:port(L),
+    Pid = spawn(fun() ->
+                        {ok, S} = gen_tcp:accept(L),
+                        (fun F() -> receive M -> F() end end)()
+                end),
+    {ok, C} = gen_tcp:connect("localhost", Port, []),
+    [begin gen_tcp:send(C,"hello"),timer:sleep(1) end || _ <- lists:seq(1,100)],
+
     %% Collect some garbage
     [erlang:garbage_collect() || _ <- lists:seq(1,100)],
 
diff --git a/erts/emulator/test/z_SUITE.erl b/erts/emulator/test/z_SUITE.erl
index feea7432a9..ac3df8bfbf 100644
--- a/erts/emulator/test/z_SUITE.erl
+++ b/erts/emulator/test/z_SUITE.erl
@@ -330,7 +330,7 @@ display_check_io(ChkIo) ->
     ok.
 
 get_check_io_info() ->
-    ChkIo = erlang:system_info(check_io),
+    ChkIo = driver_SUITE:get_check_io_total(erlang:system_info(check_io)),
     PendUpdNo = case lists:keysearch(pending_updates, 1, ChkIo) of
 		    {value, {pending_updates, PendNo}} ->
 			PendNo;