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authorRickard Green <rickard@erlang.org>2012-01-11 17:53:16 +0100
committerRickard Green <rickard@erlang.org>2012-01-26 14:04:28 +0100
commitd39e5702b224592bc79cc3ca122dcb0b59162d7f (patch)
tree26ad2d8a66b1984615f0b361e85e356fbc995b4f /erts
parenta67091debf20c972dd7ce1a8379fee6673fbe571 (diff)
downloadotp-d39e5702b224592bc79cc3ca122dcb0b59162d7f.tar.gz
otp-d39e5702b224592bc79cc3ca122dcb0b59162d7f.tar.bz2
otp-d39e5702b224592bc79cc3ca122dcb0b59162d7f.zip
Implement statistics(scheduler_wall_time)
Diffstat (limited to 'erts')
-rw-r--r--erts/emulator/beam/atom.names3
-rw-r--r--erts/emulator/beam/bif.c18
-rw-r--r--erts/emulator/beam/erl_alloc.types2
-rw-r--r--erts/emulator/beam/erl_bif_info.c11
-rw-r--r--erts/emulator/beam/erl_process.c252
-rw-r--r--erts/emulator/beam/erl_process.h14
-rw-r--r--erts/preloaded/ebin/erlang.beambin41136 -> 42416 bytes
-rw-r--r--erts/preloaded/src/erlang.erl34
8 files changed, 327 insertions, 7 deletions
diff --git a/erts/emulator/beam/atom.names b/erts/emulator/beam/atom.names
index 71454b3e57..7be40976f6 100644
--- a/erts/emulator/beam/atom.names
+++ b/erts/emulator/beam/atom.names
@@ -95,6 +95,7 @@ atom atom
atom atom_used
atom attributes
atom await_proc_exit
+atom await_sched_wall_time_modifications
atom awaiting_load
atom awaiting_unload
atom backtrace backtrace_depth
@@ -239,6 +240,7 @@ atom generational
atom get_seq_token
atom get_tcw
atom getenv
+atom gather_sched_wall_time_result
atom getting_linked
atom getting_unlinked
atom global
@@ -554,6 +556,7 @@ atom waiting
atom wall_clock
atom warning
atom warning_msg
+atom scheduler_wall_time
atom wordsize
atom write_concurrency
atom xor
diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c
index 55f4798892..f8305944a4 100644
--- a/erts/emulator/beam/bif.c
+++ b/erts/emulator/beam/bif.c
@@ -43,6 +43,9 @@ static Export* set_cpu_topology_trap = NULL;
static Export* await_proc_exit_trap = NULL;
Export* erts_format_cpu_topology_trap = NULL;
+static Export *await_sched_wall_time_mod_trap;
+static erts_smp_atomic32_t sched_wall_time;
+
#define DECL_AM(S) Eterm AM_ ## S = am_atom_put(#S, sizeof(#S) - 1)
/*
@@ -4160,6 +4163,18 @@ BIF_RETTYPE system_flag_2(BIF_ALIST_2)
erts_smp_proc_lock(BIF_P, ERTS_PROC_LOCK_MAIN);
BIF_RET(am_true);
+ } else if (BIF_ARG_1 == am_scheduler_wall_time) {
+ if (BIF_ARG_2 == am_true || BIF_ARG_2 == am_false) {
+ erts_aint32_t new = BIF_ARG_2 == am_true ? 1 : 0;
+ erts_aint32_t old = erts_smp_atomic32_xchg_nob(&sched_wall_time,
+ new);
+ Eterm ref = erts_sched_wall_time_request(BIF_P, 1, new);
+ ASSERT(is_value(ref));
+ BIF_TRAP2(await_sched_wall_time_mod_trap,
+ BIF_P,
+ ref,
+ old ? am_true : am_false);
+ }
} else if (ERTS_IS_ATOM_STR("scheduling_statistics", BIF_ARG_1)) {
int what;
if (ERTS_IS_ATOM_STR("disable", BIF_ARG_2))
@@ -4457,6 +4472,9 @@ void erts_init_bif(void)
am_format_cpu_topology,
1);
await_proc_exit_trap = erts_export_put(am_erlang,am_await_proc_exit,3);
+ await_sched_wall_time_mod_trap
+ = erts_export_put(am_erlang, am_await_sched_wall_time_modifications, 2);
+ erts_smp_atomic32_init_nob(&sched_wall_time, 0);
}
#ifdef HARDDEBUG
diff --git a/erts/emulator/beam/erl_alloc.types b/erts/emulator/beam/erl_alloc.types
index 962db8b831..90a6c0cbee 100644
--- a/erts/emulator/beam/erl_alloc.types
+++ b/erts/emulator/beam/erl_alloc.types
@@ -367,6 +367,7 @@ type EXPORT LONG_LIVED_LOW CODE export_entry
type MONITOR_SH STANDARD_LOW PROCESSES monitor_sh
type NLINK_SH STANDARD_LOW PROCESSES nlink_sh
type AINFO_REQ STANDARD_LOW SYSTEM alloc_info_request
+type SCHED_WTIME_REQ STANDARD_LOW SYSTEM sched_wall_time_request
+else # "fullword"
@@ -383,6 +384,7 @@ type EXPORT LONG_LIVED CODE export_entry
type MONITOR_SH FIXED_SIZE PROCESSES monitor_sh
type NLINK_SH FIXED_SIZE PROCESSES nlink_sh
type AINFO_REQ SHORT_LIVED SYSTEM alloc_info_request
+type SCHED_WTIME_REQ SHORT_LIVED SYSTEM sched_wall_time_request
+endif
diff --git a/erts/emulator/beam/erl_bif_info.c b/erts/emulator/beam/erl_bif_info.c
index 5a806777fe..ebd475f73a 100644
--- a/erts/emulator/beam/erl_bif_info.c
+++ b/erts/emulator/beam/erl_bif_info.c
@@ -57,6 +57,8 @@
static Export* alloc_info_trap = NULL;
static Export* alloc_sizes_trap = NULL;
+static Export *gather_sched_wall_time_res_trap;
+
#define DECL_AM(S) Eterm AM_ ## S = am_atom_put(#S, sizeof(#S) - 1)
/* Keep erts_system_version as a global variable for easy access from a core */
@@ -3180,7 +3182,12 @@ BIF_RETTYPE statistics_1(BIF_ALIST_1)
Eterm res;
Eterm* hp;
- if (BIF_ARG_1 == am_context_switches) {
+ if (BIF_ARG_1 == am_scheduler_wall_time) {
+ res = erts_sched_wall_time_request(BIF_P, 0, 0);
+ if (is_non_value(res))
+ BIF_RET(am_undefined);
+ BIF_TRAP1(gather_sched_wall_time_res_trap, BIF_P, res);
+ } else if (BIF_ARG_1 == am_context_switches) {
Eterm cs = erts_make_integer(erts_get_total_context_switches(), BIF_P);
hp = HAlloc(BIF_P, 3);
res = TUPLE2(hp, cs, SMALL_ZERO);
@@ -4160,6 +4167,8 @@ erts_bif_info_init(void)
alloc_info_trap = erts_export_put(am_erlang, am_alloc_info, 1);
alloc_sizes_trap = erts_export_put(am_erlang, am_alloc_sizes, 1);
+ gather_sched_wall_time_res_trap
+ = erts_export_put(am_erlang, am_gather_sched_wall_time_result, 1);
process_info_init();
os_info_init();
}
diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index b8c6b64fc0..c6226cd9d0 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -537,6 +537,209 @@ erts_late_init_process(void)
}
+static void
+init_sched_wall_time(ErtsSchedWallTime *swtp)
+{
+ swtp->enabled = 0;
+ swtp->start = 0;
+ swtp->working.total = 0;
+ swtp->working.start = 0;
+ swtp->working.currently = 0;
+}
+
+static ERTS_INLINE Uint64
+sched_wall_time_ts(void)
+{
+#ifdef HAVE_GETHRTIME
+ return (Uint64) sys_gethrtime();
+#else
+ Uint64 res;
+ SysTimeval tv;
+ sys_gettimeofday(&tv);
+ res = (Uint64) tv.tv_sec*1000000;
+ res += (Uint64) tv.tv_usec;
+ return res;
+#endif
+}
+
+static ERTS_INLINE void
+sched_wall_time_change(ErtsSchedulerData *esdp, int working)
+{
+ if (esdp->sched_wall_time.enabled) {
+ Uint64 ts = sched_wall_time_ts();
+ if (working) {
+#ifdef DEBUG
+ ASSERT(!esdp->sched_wall_time.working.currently);
+ esdp->sched_wall_time.working.currently = 1;
+#endif
+ ts -= esdp->sched_wall_time.start;
+ esdp->sched_wall_time.working.start = ts;
+ }
+ else {
+#ifdef DEBUG
+ ASSERT(esdp->sched_wall_time.working.currently);
+ esdp->sched_wall_time.working.currently = 0;
+#endif
+ ts -= esdp->sched_wall_time.start;
+ ts -= esdp->sched_wall_time.working.start;
+ esdp->sched_wall_time.working.total += ts;
+ }
+ }
+}
+
+typedef struct {
+ int set;
+ int enable;
+ Process *proc;
+ Eterm ref;
+ Eterm ref_heap[REF_THING_SIZE];
+ Uint req_sched;
+ erts_smp_atomic32_t refc;
+} ErtsSchedWallTimeReq;
+
+#if !HALFWORD_HEAP
+ERTS_SCHED_PREF_QUICK_ALLOC_IMPL(swtreq,
+ ErtsSchedWallTimeReq,
+ 5,
+ ERTS_ALC_T_SCHED_WTIME_REQ)
+#else
+static ERTS_INLINE ErtsSchedWallTimeReq *
+swtreq_alloc(void)
+{
+ return erts_alloc(ERTS_ALC_T_SCHED_WTIME_REQ,
+ sizeof(ErtsSchedWallTimeReq));
+}
+
+static ERTS_INLINE void
+swtreq_free(ErtsSchedWallTimeReq *ptr)
+{
+ erts_free(ERTS_ALC_T_SCHED_WTIME_REQ, ptr);
+}
+#endif
+
+static void
+reply_sched_wall_time(void *vswtrp)
+{
+ Uint64 working = 0, total = 0;
+ ErtsSchedulerData *esdp = erts_get_scheduler_data();
+ ErtsSchedWallTimeReq *swtrp = (ErtsSchedWallTimeReq *) vswtrp;
+ ErtsProcLocks rp_locks = (swtrp->req_sched == esdp->no
+ ? ERTS_PROC_LOCK_MAIN
+ : 0);
+ Process *rp = swtrp->proc;
+ Eterm ref_copy = NIL, msg;
+ Eterm *hp = NULL;
+ Eterm **hpp;
+ Uint sz, *szp;
+ ErlOffHeap *ohp = NULL;
+ ErlHeapFragment *bp = NULL;
+
+ ASSERT(esdp);
+
+ if (swtrp->set) {
+ if (!swtrp->enable && esdp->sched_wall_time.enabled)
+ esdp->sched_wall_time.enabled = 0;
+ else if (swtrp->enable && !esdp->sched_wall_time.enabled) {
+ Uint64 ts = sched_wall_time_ts();
+ esdp->sched_wall_time.enabled = 1;
+ esdp->sched_wall_time.start = ts;
+ esdp->sched_wall_time.working.total = 0;
+ esdp->sched_wall_time.working.start = 0;
+ esdp->sched_wall_time.working.currently = 1;
+ }
+ }
+
+ if (esdp->sched_wall_time.enabled) {
+ Uint64 ts = sched_wall_time_ts();
+ ASSERT(esdp->sched_wall_time.working.currently);
+ ts -= esdp->sched_wall_time.start;
+ total = ts;
+ ts -= esdp->sched_wall_time.working.start;
+ working = esdp->sched_wall_time.working.total + ts;
+ }
+
+ sz = 0;
+ hpp = NULL;
+ szp = &sz;
+
+ while (1) {
+ if (hpp)
+ ref_copy = STORE_NC(hpp, ohp, swtrp->ref);
+ else
+ *szp += REF_THING_SIZE;
+
+ if (swtrp->set)
+ msg = ref_copy;
+ else {
+ msg = (!esdp->sched_wall_time.enabled
+ ? am_notsup
+ : erts_bld_tuple(hpp, szp, 3,
+ make_small(esdp->no),
+ erts_bld_uint64(hpp, szp, working),
+ erts_bld_uint64(hpp, szp, total)));
+
+ msg = erts_bld_tuple(hpp, szp, 2, ref_copy, msg);
+ }
+ if (hpp)
+ break;
+
+ hp = erts_alloc_message_heap(sz, &bp, &ohp, rp, &rp_locks);
+ szp = NULL;
+ hpp = &hp;
+ }
+
+ erts_queue_message(rp, &rp_locks, bp, msg, NIL);
+
+ if (swtrp->req_sched == esdp->no)
+ rp_locks &= ~ERTS_PROC_LOCK_MAIN;
+
+ if (rp_locks)
+ erts_smp_proc_unlock(rp, rp_locks);
+
+ erts_smp_proc_dec_refc(rp);
+
+ if (erts_smp_atomic32_dec_read_nob(&swtrp->refc) == 0)
+ swtreq_free(vswtrp);
+}
+
+Eterm
+erts_sched_wall_time_request(Process *c_p, int set, int enable)
+{
+ ErtsSchedulerData *esdp = ERTS_PROC_GET_SCHDATA(c_p);
+ Eterm ref;
+ ErtsSchedWallTimeReq *swtrp;
+ Eterm *hp;
+
+ if (!set && !esdp->sched_wall_time.enabled)
+ return THE_NON_VALUE;
+
+ swtrp = swtreq_alloc();
+ ref = erts_make_ref(c_p);
+ hp = &swtrp->ref_heap[0];
+
+ swtrp->set = set;
+ swtrp->enable = enable;
+ swtrp->proc = c_p;
+ swtrp->ref = STORE_NC(&hp, NULL, ref);
+ swtrp->req_sched = esdp->no;
+ erts_smp_atomic32_init_nob(&swtrp->refc,
+ (erts_aint32_t) erts_no_schedulers);
+
+ erts_smp_proc_add_refc(c_p, (Sint32) erts_no_schedulers);
+
+#ifdef ERTS_SMP
+ if (erts_no_schedulers > 1)
+ erts_schedule_multi_misc_aux_work(1,
+ erts_no_schedulers,
+ reply_sched_wall_time,
+ (void *) swtrp);
+#endif
+
+ reply_sched_wall_time((void *) swtrp);
+
+ return ref;
+}
+
static ERTS_INLINE ErtsProcList *
proclist_create(Process *p)
{
@@ -1707,6 +1910,7 @@ aux_thread(void *unused)
static void
scheduler_wait(int *fcalls, ErtsSchedulerData *esdp, ErtsRunQueue *rq)
{
+ int working = 1;
ErtsSchedulerSleepInfo *ssi = esdp->ssi;
int spincount;
erts_aint32_t aux_work = 0;
@@ -1737,12 +1941,17 @@ scheduler_wait(int *fcalls, ErtsSchedulerData *esdp, ErtsRunQueue *rq)
tse_wait:
+ if (thr_prgr_active != working)
+ sched_wall_time_change(esdp, thr_prgr_active);
+
while (1) {
aux_work = erts_atomic32_read_acqb(&ssi->aux_work);
if (aux_work) {
- if (!thr_prgr_active)
+ 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);
if (aux_work && erts_thr_progress_update(esdp))
erts_thr_progress_leader_update(esdp);
@@ -1751,8 +1960,10 @@ scheduler_wait(int *fcalls, ErtsSchedulerData *esdp, ErtsRunQueue *rq)
if (aux_work)
flgs = erts_smp_atomic32_read_acqb(&ssi->flags);
else {
- if (thr_prgr_active)
+ 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_wait(ssi, spincount);
@@ -1789,8 +2000,10 @@ scheduler_wait(int *fcalls, ErtsSchedulerData *esdp, ErtsRunQueue *rq)
if (flgs & ~ERTS_SSI_FLG_SUSPENDED)
erts_smp_atomic32_read_band_nob(&ssi->flags, ERTS_SSI_FLG_SUSPENDED);
- if (!thr_prgr_active)
+ if (!thr_prgr_active) {
erts_thr_progress_active(esdp, thr_prgr_active = 1);
+ sched_wall_time_change(esdp, 1);
+ }
erts_smp_runq_lock(rq);
sched_active(esdp->no, rq);
@@ -1806,14 +2019,21 @@ scheduler_wait(int *fcalls, ErtsSchedulerData *esdp, ErtsRunQueue *rq)
sched_waiting_sys(esdp->no, rq);
+
erts_smp_runq_unlock(rq);
+ ASSERT(working);
+ sched_wall_time_change(esdp, working = 0);
+
spincount = ERTS_SCHED_SYS_SLEEP_SPINCOUNT;
while (spincount-- > 0) {
sys_poll_aux_work:
+ if (working)
+ sched_wall_time_change(esdp, working = 0);
+
ASSERT(!erts_port_task_have_outstanding_io_tasks());
erl_sys_schedule(1); /* Might give us something to do */
@@ -1828,6 +2048,8 @@ scheduler_wait(int *fcalls, ErtsSchedulerData *esdp, ErtsRunQueue *rq)
aux_work = erts_atomic32_read_acqb(&ssi->aux_work);
if (aux_work) {
+ if (!working)
+ sched_wall_time_change(esdp, working = 1);
#ifdef ERTS_SMP
if (!thr_prgr_active)
erts_thr_progress_active(esdp, thr_prgr_active = 1);
@@ -1920,6 +2142,9 @@ scheduler_wait(int *fcalls, ErtsSchedulerData *esdp, ErtsRunQueue *rq)
erts_smp_runq_unlock(rq);
+ if (working)
+ sched_wall_time_change(esdp, working = 0);
+
#ifdef ERTS_SMP
if (thr_prgr_active)
erts_thr_progress_active(esdp, thr_prgr_active = 0);
@@ -1955,6 +2180,8 @@ scheduler_wait(int *fcalls, ErtsSchedulerData *esdp, ErtsRunQueue *rq)
if (flgs & ~ERTS_SSI_FLG_SUSPENDED)
erts_smp_atomic32_read_band_nob(&ssi->flags, ERTS_SSI_FLG_SUSPENDED);
#endif
+ if (!working)
+ sched_wall_time_change(esdp, working = 1);
sched_active_sys(esdp->no, rq);
}
@@ -3430,9 +3657,14 @@ erts_init_scheduling(int no_schedulers, int no_schedulers_online)
esdp->run_queue->scheduler = esdp;
init_aux_work_data(&esdp->aux_work_data, esdp);
+ init_sched_wall_time(&esdp->sched_wall_time);
}
init_misc_aux_work();
+#if !HALFWORD_HEAP
+ init_swtreq_alloc();
+#endif
+
#ifdef ERTS_SMP
@@ -3755,6 +3987,8 @@ suspend_scheduler(ErtsSchedulerData *esdp)
if (erts_system_profile_flags.scheduler)
profile_scheduler(make_small(esdp->no), am_inactive);
+ sched_wall_time_change(esdp, 0);
+
erts_smp_mtx_lock(&schdlr_sspnd.mtx);
flgs = sched_prep_spin_suspended(ssi, ERTS_SSI_FLG_SUSPENDED);
@@ -3813,16 +4047,20 @@ suspend_scheduler(ErtsSchedulerData *esdp)
aux_work = erts_atomic32_read_acqb(&ssi->aux_work);
if (aux_work) {
- if (!thr_prgr_active)
+ 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);
if (aux_work && erts_thr_progress_update(esdp))
erts_thr_progress_leader_update(esdp);
}
if (!aux_work) {
- if (thr_prgr_active)
+ 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);
@@ -3877,8 +4115,10 @@ suspend_scheduler(ErtsSchedulerData *esdp)
if (erts_system_profile_flags.scheduler)
profile_scheduler(make_small(esdp->no), am_active);
- if (!thr_prgr_active)
+ if (!thr_prgr_active) {
erts_thr_progress_active(esdp, thr_prgr_active = 1);
+ sched_wall_time_change(esdp, 1);
+ }
erts_smp_runq_lock(esdp->run_queue);
non_empty_runq(esdp->run_queue);
diff --git a/erts/emulator/beam/erl_process.h b/erts/emulator/beam/erl_process.h
index a51b380bb0..173b7df69d 100644
--- a/erts/emulator/beam/erl_process.h
+++ b/erts/emulator/beam/erl_process.h
@@ -394,6 +394,16 @@ do { \
} while (0)
typedef struct {
+ int enabled;
+ Uint64 start;
+ struct {
+ Uint64 total;
+ Uint64 start;
+ int currently;
+ } working;
+} ErtsSchedWallTime;
+
+typedef struct {
int sched_id;
ErtsSchedulerData *esdp;
ErtsSchedulerSleepInfo *ssi;
@@ -457,6 +467,8 @@ struct ErtsSchedulerData_ {
ErtsSchedAllocData alloc_data;
+ ErtsSchedWallTime sched_wall_time;
+
#ifdef ERTS_DO_VERIFY_UNUSED_TEMP_ALLOC
erts_alloc_verify_func_t verify_unused_temp_alloc;
Allctr_t *verify_unused_temp_alloc_data;
@@ -1064,6 +1076,8 @@ void erts_late_init_process(void);
void erts_early_init_scheduling(int);
void erts_init_scheduling(int, int);
+Eterm erts_sched_wall_time_request(Process *c_p, int set, int enable);
+
ErtsProcList *erts_proclist_create(Process *);
void erts_proclist_destroy(ErtsProcList *);
int erts_proclist_same(ErtsProcList *, Process *);
diff --git a/erts/preloaded/ebin/erlang.beam b/erts/preloaded/ebin/erlang.beam
index 9e369d5348..b78747bc84 100644
--- a/erts/preloaded/ebin/erlang.beam
+++ b/erts/preloaded/ebin/erlang.beam
Binary files differ
diff --git a/erts/preloaded/src/erlang.erl b/erts/preloaded/src/erlang.erl
index 4affc9bffe..4cbff3f36e 100644
--- a/erts/preloaded/src/erlang.erl
+++ b/erts/preloaded/src/erlang.erl
@@ -43,6 +43,9 @@
-export([memory/0, memory/1]).
-export([alloc_info/1, alloc_sizes/1]).
+-export([gather_sched_wall_time_result/1,
+ await_sched_wall_time_modifications/2]).
+
-deprecated([hash/2]).
% Get rid of autoimports of spawn to avoid clashes with ourselves.
@@ -1202,3 +1205,34 @@ receive_allocator(Ref, N, Acc) ->
{Ref, _, InfoList} ->
receive_allocator(Ref, N-1, insert_info(InfoList, Acc))
end.
+
+-spec await_sched_wall_time_modifications(Ref, Result) -> boolean() when
+ Ref :: reference(),
+ Result :: boolean().
+
+await_sched_wall_time_modifications(Ref, Result) ->
+ sched_wall_time(Ref, erlang:system_info(schedulers)),
+ Result.
+
+-spec gather_sched_wall_time_result(Ref) -> [{pos_integer(),
+ non_neg_integer(),
+ non_neg_integer()}] when
+ Ref :: reference().
+
+gather_sched_wall_time_result(Ref) when is_reference(Ref) ->
+ sched_wall_time(Ref, erlang:system_info(schedulers), []).
+
+sched_wall_time(_Ref, 0) ->
+ ok;
+sched_wall_time(Ref, N) ->
+ receive Ref -> sched_wall_time(Ref, N-1) end.
+
+sched_wall_time(_Ref, 0, Acc) ->
+ Acc;
+sched_wall_time(Ref, N, undefined) ->
+ receive {Ref, _} -> sched_wall_time(Ref, N-1, undefined) end;
+sched_wall_time(Ref, N, Acc) ->
+ receive
+ {Ref, undefined} -> sched_wall_time(Ref, N-1, undefined);
+ {Ref, SWT} -> sched_wall_time(Ref, N-1, [SWT|Acc])
+ end.