3 files changed, 102 insertions, 3 deletions

diff --git a/erts/emulator/beam/erl_init.c b/erts/emulator/beam/erl_init.c
index 2fb73aed96..4bae3dfeb4 100644
--- a/erts/emulator/beam/erl_init.c
+++ b/erts/emulator/beam/erl_init.c
@@ -1480,6 +1480,22 @@ erl_start(int argc, char **argv)
 			("suggested scheduler thread stack size %d kilo words\n",
 			 erts_sched_thread_suggested_stack_size));
 	    }
+	    else if (has_prefix("fwi", sub_param)) {
+		long val;
+		arg = get_arg(sub_param+3, argv[i+1], &i);
+		errno = 0;
+		val = strtol(arg, NULL, 10);
+		if (errno != 0 || val < 0) {
+		    erts_fprintf(stderr,
+				 "bad scheduler forced wakeup "
+				 "interval %s\n",
+				 arg);
+		    erts_usage();
+		}
+#ifdef ERTS_SMP
+		erts_runq_supervision_interval = val;
+#endif
+	    }
 	    else {
 		erts_fprintf(stderr, "bad scheduling option %s\n", argv[i]);
 		erts_usage();
diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index 64b4c25ba0..2439a46ab6 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -246,6 +246,10 @@ static erts_smp_atomic32_t function_calls;
 #ifdef ERTS_SMP
 static erts_smp_atomic32_t doing_sys_schedule;
 static erts_smp_atomic32_t no_empty_run_queues;
+long erts_runq_supervision_interval = 0;
+static ethr_event runq_supervision_event;
+static erts_tid_t runq_supervisor_tid;
+static erts_atomic_t runq_supervisor_sleeping;
 #else /* !ERTS_SMP */
 ErtsSchedulerData *erts_scheduler_data;
 #endif
@@ -2045,7 +2049,13 @@ empty_runq(ErtsRunQueue *rq)
 	 */
 	ASSERT(0 <= empty && empty < 2*erts_no_run_queues);
 #endif
-	erts_smp_atomic32_inc_relb(&no_empty_run_queues);
+	if (!erts_runq_supervision_interval)
+	    erts_smp_atomic32_inc_relb(&no_empty_run_queues);
+	else {
+	    erts_smp_atomic32_inc_mb(&no_empty_run_queues);
+	    if (erts_atomic_read_nob(&runq_supervisor_sleeping))
+		ethr_event_set(&runq_supervision_event);
+	}
     }
 }
 
@@ -2062,7 +2072,14 @@ non_empty_runq(ErtsRunQueue *rq)
 	 */
 	ASSERT(0 < empty && empty <= 2*erts_no_run_queues);
 #endif
-	erts_smp_atomic32_dec_relb(&no_empty_run_queues);
+	if (!erts_runq_supervision_interval)
+	    erts_smp_atomic32_dec_relb(&no_empty_run_queues);
+	else {
+	    erts_aint32_t no;
+	    no = erts_smp_atomic32_dec_read_mb(&no_empty_run_queues);
+	    if (no > 0 && erts_atomic_read_nob(&runq_supervisor_sleeping))
+		ethr_event_set(&runq_supervision_event);
+	}
     }
 }
 
@@ -2666,7 +2683,6 @@ try_inc_no_active_runqs(int active)
     return 0;
 }
 
-
 static ERTS_INLINE int
 chk_wake_sched(ErtsRunQueue *crq, int ix, int activate)
 {
@@ -4332,6 +4348,53 @@ set_wakeup_other_data(void)
     }
 }
 
+static int
+no_runqs_to_supervise(void)
+{
+    int used;
+    erts_aint32_t nerq = erts_smp_atomic32_read_acqb(&no_empty_run_queues);
+    if (nerq <= 0)
+	return 0;
+    get_no_runqs(NULL, &used);
+    if (nerq >= used)
+	return 0;
+    return used;
+}
+
+static void *
+runq_supervisor(void *unused)
+{
+    while (1) {
+	int ix, no_rqs;
+
+	erts_milli_sleep(erts_runq_supervision_interval);
+	no_rqs = no_runqs_to_supervise();
+	if (!no_rqs) {
+	    erts_atomic_set_nob(&runq_supervisor_sleeping, 1);
+	    while (1) {
+		ethr_event_reset(&runq_supervision_event);
+		no_rqs = no_runqs_to_supervise();
+		if (no_rqs) {
+		    erts_atomic_set_nob(&runq_supervisor_sleeping, 0);
+		    break;
+		}
+		ethr_event_wait(&runq_supervision_event);
+	    }
+	}
+
+	for (ix = 0; ix < no_rqs; ix++) {
+	    ErtsRunQueue *rq = ERTS_RUNQ_IX(ix);
+	    if (ERTS_RUNQ_FLGS_GET(rq) & ERTS_RUNQ_FLG_NONEMPTY) {
+		erts_smp_runq_lock(rq);
+		if (rq->len != 0)
+		    wake_scheduler_on_empty_runq(rq); /* forced wakeup... */
+		erts_smp_runq_unlock(rq);
+	    }
+	}
+    }
+    return NULL;
+}
+
 #endif
 
 void
@@ -5755,6 +5818,22 @@ erts_start_schedulers(void)
     ethr_thr_opts opts = ETHR_THR_OPTS_DEFAULT_INITER;
 
     opts.detached = 1;
+
+#ifdef ERTS_SMP
+    if (erts_runq_supervision_interval) {
+	opts.suggested_stack_size = 16;
+	erts_atomic_init_nob(&runq_supervisor_sleeping, 0);
+	if (0 != ethr_event_init(&runq_supervision_event))
+	    erl_exit(1, "Failed to create run-queue supervision event\n");
+	if (0 != ethr_thr_create(&runq_supervisor_tid,
+				 runq_supervisor,
+				 NULL,
+				 &opts))
+	    erl_exit(1, "Failed to create run-queue supervision thread\n");
+
+    }
+#endif
+
     opts.suggested_stack_size = erts_sched_thread_suggested_stack_size;
 
     if (wanted < 1)
diff --git a/erts/emulator/beam/erl_process.h b/erts/emulator/beam/erl_process.h
index 973db65490..24568af24d 100644
--- a/erts/emulator/beam/erl_process.h
+++ b/erts/emulator/beam/erl_process.h
@@ -387,6 +387,10 @@ struct ErtsRunQueue_ {
     } ports;
 };
 
+#ifdef ERTS_SMP
+extern long erts_runq_supervision_interval;
+#endif
+
 typedef union {
     ErtsRunQueue runq;
     char align[ERTS_ALC_CACHE_LINE_ALIGN_SIZE(sizeof(ErtsRunQueue))];