Reduce number of atomic ops

Counters for active, and used schedulers have been coalesced in
order to reduce the amount of atomic operations needed.

Some currently not strictly necessary barriers have also been added
in order to be future proof.

1 files changed, 100 insertions, 35 deletions

diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index 31f23d3978..559224be58 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -166,9 +166,8 @@ static struct {
 
 static struct {
     erts_smp_mtx_t update_mtx;
-    erts_smp_atomic32_t active_runqs;
+    erts_smp_atomic32_t no_runqs;
     int last_active_runqs;
-    erts_smp_atomic32_t used_runqs;
     int forced_check_balance;
     erts_smp_atomic32_t checking_balance;
     int halftime;
@@ -965,7 +964,7 @@ sched_spin_wait(ErtsSchedulerSleepInfo *ssi, int spincount)
     erts_aint32_t flgs;
 
     do {
-	flgs = erts_smp_atomic32_read(&ssi->flags);
+	flgs = erts_smp_atomic32_read_acqb(&ssi->flags);
 	if ((flgs & (ERTS_SSI_FLG_SLEEPING|ERTS_SSI_FLG_WAITING))
 	    != (ERTS_SSI_FLG_SLEEPING|ERTS_SSI_FLG_WAITING)) {
 	    break;
@@ -1114,7 +1113,7 @@ scheduler_wait(int *fcalls, ErtsSchedulerData *esdp, ErtsRunQueue *rq)
     else {
 	erts_aint_t dt;
 
-	erts_smp_atomic32_set(&function_calls, 0);
+	erts_smp_atomic32_set_relb(&function_calls, 0);
 	*fcalls = 0;
 
 	sched_waiting_sys(esdp->no, rq);
@@ -1147,7 +1146,7 @@ scheduler_wait(int *fcalls, ErtsSchedulerData *esdp, ErtsRunQueue *rq)
 	    nonblockable_aux_work(esdp, ssi, aux_work);
 #endif
 
-	    flgs = erts_smp_atomic32_read(&ssi->flags);
+	    flgs = erts_smp_atomic32_read_acqb(&ssi->flags);
 	    if (!(flgs & ERTS_SSI_FLG_WAITING)) {
 		ASSERT(!(flgs & ERTS_SSI_FLG_SLEEPING));
 		goto sys_woken;
@@ -1333,6 +1332,76 @@ wake_all_schedulers(void)
     }
 }
 
+#define ERTS_NO_USED_RUNQS_SHIFT 16
+#define ERTS_NO_RUNQS_MASK 0xffff
+
+#if ERTS_MAX_NO_OF_SCHEDULERS > ERTS_NO_RUNQS_MASK
+#  error "Too large amount of schedulers allowed"
+#endif
+
+static ERTS_INLINE void
+init_no_runqs(int active, int used)
+{
+    erts_aint32_t no_runqs = (erts_aint32_t) (active & ERTS_NO_RUNQS_MASK);
+    no_runqs |= (erts_aint32_t) ((used & ERTS_NO_RUNQS_MASK) << ERTS_NO_USED_RUNQS_SHIFT);
+    erts_smp_atomic32_init(&balance_info.no_runqs, no_runqs);
+}
+
+static ERTS_INLINE void
+get_no_runqs(int *active, int *used)
+{
+    erts_aint32_t no_runqs = erts_smp_atomic32_read(&balance_info.no_runqs);
+    if (active)
+	*active = (int) (no_runqs & ERTS_NO_RUNQS_MASK);
+    if (used)
+	*used = (int) ((no_runqs >> ERTS_NO_USED_RUNQS_SHIFT) & ERTS_NO_RUNQS_MASK);
+}
+
+static ERTS_INLINE void
+set_no_used_runqs(int used)
+{
+    erts_aint32_t exp = erts_smp_atomic32_read(&balance_info.no_runqs);
+    while (1) {
+	erts_aint32_t act, new;
+	new = (used << ERTS_NO_USED_RUNQS_SHIFT) | (exp & ERTS_NO_RUNQS_MASK);
+	act = erts_smp_atomic32_cmpxchg(&balance_info.no_runqs, new, exp);
+	if (act == exp)
+	    break;
+	exp = act;
+    }
+}
+
+static ERTS_INLINE void
+set_no_active_runqs(int active)
+{
+    erts_aint32_t exp = erts_smp_atomic32_read(&balance_info.no_runqs);
+    while (1) {
+	erts_aint32_t act, new;
+	new = (exp & (ERTS_NO_RUNQS_MASK << ERTS_NO_USED_RUNQS_SHIFT)) | active;
+	act = erts_smp_atomic32_cmpxchg(&balance_info.no_runqs, new, exp);
+	if (act == exp)
+	    break;
+	exp = act;
+    }
+}
+
+static ERTS_INLINE int
+try_inc_no_active_runqs(int active)
+{
+    erts_aint32_t exp = erts_smp_atomic32_read(&balance_info.no_runqs);
+    if (((exp >> ERTS_NO_USED_RUNQS_SHIFT) & ERTS_NO_RUNQS_MASK) < active)
+	return 0;
+    if ((exp & ERTS_NO_RUNQS_MASK) + 1 == active) {
+	erts_aint32_t new, act;
+	new = (exp & ~ERTS_NO_RUNQS_MASK) | active;
+	act = erts_smp_atomic32_cmpxchg(&balance_info.no_runqs, new, exp);
+	if (act == exp)
+	    return 1;
+    }
+    return 0;
+}
+
+
 static ERTS_INLINE int
 chk_wake_sched(ErtsRunQueue *crq, int ix, int activate)
 {
@@ -1344,9 +1413,7 @@ chk_wake_sched(ErtsRunQueue *crq, int ix, int activate)
     iflgs = erts_smp_atomic32_read(&wrq->info_flags);
     if (!(iflgs & (ERTS_RUNQ_IFLG_SUSPENDED|ERTS_RUNQ_IFLG_NONEMPTY))) {
 	if (activate) {
-	    if (ix == erts_smp_atomic32_cmpxchg(&balance_info.active_runqs,
-						ix+1,
-						ix)) {
+	    if (try_inc_no_active_runqs(ix+1)) {
 		erts_smp_xrunq_lock(crq, wrq);
 		wrq->flags &= ~ERTS_RUNQ_FLG_INACTIVE;
 		erts_smp_xrunq_unlock(crq, wrq);
@@ -1363,8 +1430,9 @@ wake_scheduler_on_empty_runq(ErtsRunQueue *crq)
 {
     int ix = crq->ix;
     int stop_ix = ix;
-    int active_ix = erts_smp_atomic32_read(&balance_info.active_runqs);
-    int balance_ix = erts_smp_atomic32_read(&balance_info.used_runqs);
+    int active_ix, balance_ix;
+
+    get_no_runqs(&active_ix, &balance_ix);
 
     if (active_ix > balance_ix)
 	active_ix = balance_ix;
@@ -1416,7 +1484,7 @@ erts_sched_notify_check_cpu_bind(void)
     int ix;
     if (erts_common_run_queue) {
 	for (ix = 0; ix < erts_no_schedulers; ix++)
-	    erts_smp_atomic32_set(&ERTS_SCHEDULER_IX(ix)->chk_cpu_bind, 1);
+	    erts_smp_atomic32_set_relb(&ERTS_SCHEDULER_IX(ix)->chk_cpu_bind, 1);
 	wake_all_schedulers();
     }
     else {
@@ -1871,8 +1939,7 @@ try_steal_task(ErtsRunQueue *rq)
 
     ERTS_SMP_LC_CHK_RUNQ_LOCK(rq, rq_locked);
 
-    active_rqs = erts_smp_atomic32_read(&balance_info.active_runqs);
-    blnc_rqs = erts_smp_atomic32_read(&balance_info.used_runqs);
+    get_no_runqs(&active_rqs, &blnc_rqs);
 
     if (active_rqs > blnc_rqs)
 	active_rqs = blnc_rqs;
@@ -1883,7 +1950,7 @@ try_steal_task(ErtsRunQueue *rq)
 	if (active_rqs < blnc_rqs) {
 	    int no = blnc_rqs - active_rqs;
 	    int stop_ix = vix = active_rqs + rq->ix % no;
-	    while (erts_smp_atomic32_read(&no_empty_run_queues) < blnc_rqs) {
+	    while (erts_smp_atomic32_read_acqb(&no_empty_run_queues) < blnc_rqs) {
 		res = check_possible_steal_victim(rq, &rq_locked, vix);
 		if (res)
 		    goto done;
@@ -1898,7 +1965,7 @@ try_steal_task(ErtsRunQueue *rq)
 	vix = rq->ix;
 
 	/* ... then try to steal a job from another active queue... */
-	while (erts_smp_atomic32_read(&no_empty_run_queues) < blnc_rqs) {
+	while (erts_smp_atomic32_read_acqb(&no_empty_run_queues) < blnc_rqs) {
 	    vix++;
 	    if (vix >= active_rqs)
 		vix = 0;
@@ -1999,7 +2066,7 @@ check_balance(ErtsRunQueue *c_rq)
 	return;
     }
 
-    blnc_no_rqs = (int) erts_smp_atomic32_read(&balance_info.used_runqs);
+    get_no_runqs(NULL, &blnc_no_rqs);
     if (blnc_no_rqs == 1) {
 	c_rq->check_balance_reds = INT_MAX;
 	erts_smp_atomic32_set(&balance_info.checking_balance, 0);
@@ -2038,7 +2105,8 @@ check_balance(ErtsRunQueue *c_rq)
     forced = balance_info.forced_check_balance;
     balance_info.forced_check_balance = 0;
 
-    blnc_no_rqs = (int) erts_smp_atomic32_read(&balance_info.used_runqs);
+    get_no_runqs(&current_active, &blnc_no_rqs);
+
     if (blnc_no_rqs == 1) {
 	erts_smp_mtx_unlock(&balance_info.update_mtx);
 	erts_smp_runq_lock(c_rq);
@@ -2052,8 +2120,6 @@ check_balance(ErtsRunQueue *c_rq)
     if (balance_info.full_reds_history_index >= ERTS_FULL_REDS_HISTORY_SIZE)
 	balance_info.full_reds_history_index = 0;
 
-    current_active = erts_smp_atomic32_read(&balance_info.active_runqs);
-
     /* Read balance information for all run queues */
     for (qix = 0; qix < blnc_no_rqs; qix++) {
 	ErtsRunQueue *rq = ERTS_RUNQ_IX(qix);
@@ -2387,7 +2453,7 @@ erts_fprintf(stderr, "--------------------------------\n");
     }
 
     balance_info.last_active_runqs = active;
-    erts_smp_atomic32_set(&balance_info.active_runqs, active);
+    set_no_active_runqs(active);
 
     balance_info.halftime = 1;
     erts_smp_atomic32_set(&balance_info.checking_balance, 0);
@@ -2695,9 +2761,8 @@ erts_init_scheduling(int mrq, int no_schedulers, int no_schedulers_online)
     erts_smp_atomic32_init(&schdlr_sspnd.msb.ongoing, 0);
     erts_smp_atomic32_init(&schdlr_sspnd.active, no_schedulers);
     schdlr_sspnd.msb.procs = NULL;
-    erts_smp_atomic32_set(&balance_info.used_runqs,
-			  erts_common_run_queue ? 1 : no_schedulers_online);
-    erts_smp_atomic32_init(&balance_info.active_runqs, no_schedulers);
+    init_no_runqs(no_schedulers,
+		  erts_common_run_queue ? 1 : no_schedulers_online);
     balance_info.last_active_runqs = no_schedulers;
     erts_smp_mtx_init(&balance_info.update_mtx, "migration_info_update");
     balance_info.forced_check_balance = 0;
@@ -2939,7 +3004,7 @@ sched_spin_suspended(ErtsSchedulerSleepInfo *ssi, int spincount)
     erts_aint32_t flgs;
 
     do {
-	flgs = erts_smp_atomic32_read(&ssi->flags);
+	flgs = erts_smp_atomic32_read_acqb(&ssi->flags);
 	if ((flgs & (ERTS_SSI_FLG_SLEEPING
 		     | ERTS_SSI_FLG_WAITING
 		     | ERTS_SSI_FLG_SUSPENDED))
@@ -3068,7 +3133,7 @@ suspend_scheduler(ErtsSchedulerData *esdp)
 		wake = 0;
 	    }
 
-	    flgs = erts_smp_atomic32_read(&ssi->flags);
+	    flgs = erts_smp_atomic32_read_acqb(&ssi->flags);
 	    if (!(flgs & ERTS_SSI_FLG_SUSPENDED))
 		break;
 	    erts_smp_mtx_unlock(&schdlr_sspnd.mtx);
@@ -3292,7 +3357,7 @@ erts_set_schedulers_online(Process *p,
 			ErtsRunQueue *to_rq = ERTS_RUNQ_IX(ix % no);
 			evacuate_run_queue(from_rq, to_rq);
 		    }
-		    erts_smp_atomic32_set(&balance_info.used_runqs, no);
+		    set_no_used_runqs(no);
 		    erts_smp_mtx_unlock(&balance_info.update_mtx);
 		    erts_smp_mtx_lock(&schdlr_sspnd.mtx);
 		}
@@ -3346,7 +3411,7 @@ erts_set_schedulers_online(Process *p,
 		    for (ix = erts_no_run_queues-1; ix >= no; ix--)
 			evacuate_run_queue(ERTS_RUNQ_IX(ix),
 					   ERTS_RUNQ_IX(ix % no));
-		    erts_smp_atomic32_set(&balance_info.used_runqs, no);
+		    set_no_used_runqs(no);
 		    erts_smp_mtx_unlock(&balance_info.update_mtx);
 		    erts_smp_mtx_lock(&schdlr_sspnd.mtx);
 		    for (ix = no; ix < online; ix++) {
@@ -3443,7 +3508,7 @@ erts_block_multi_scheduling(Process *p, ErtsProcLocks plocks, int on, int all)
 		else {
 		    erts_smp_mtx_unlock(&schdlr_sspnd.mtx);
 		    erts_smp_mtx_lock(&balance_info.update_mtx);
-		    erts_smp_atomic32_set(&balance_info.used_runqs, 1);
+		    set_no_used_runqs(1);
 		    for (ix = 0; ix < online; ix++) {
 			ErtsRunQueue *rq = ERTS_RUNQ_IX(ix);
 			erts_smp_runq_lock(rq);
@@ -3580,7 +3645,7 @@ erts_block_multi_scheduling(Process *p, ErtsProcLocks plocks, int on, int all)
 		    evacuate_run_queue(ERTS_RUNQ_IX(ix),
 				       ERTS_RUNQ_IX(ix % online));
 
-		erts_smp_atomic32_set(&balance_info.used_runqs, online);
+		set_no_used_runqs(online);
 		/* Make sure that we balance soon... */
 		balance_info.forced_check_balance = 1;
 		erts_smp_runq_lock(ERTS_RUNQ_IX(0));
@@ -5097,7 +5162,7 @@ Process *schedule(Process *p, int calls)
 	esdp = erts_get_scheduler_data();
 	rq = erts_get_runq_current(esdp);
 	ASSERT(esdp);
-	fcalls = (int) erts_smp_atomic32_read(&function_calls);
+	fcalls = (int) erts_smp_atomic32_read_acqb(&function_calls);
 	actual_reds = reds = 0;
 	erts_smp_runq_lock(rq);
     } else {
@@ -5248,14 +5313,14 @@ Process *schedule(Process *p, int calls)
 			 | ERTS_RUNQ_FLG_CHK_CPU_BIND
 			 | ERTS_RUNQ_FLG_SUSPENDED)) {
 	    if ((rq->flags & ERTS_RUNQ_FLG_SUSPENDED)
-		|| (erts_smp_atomic32_read(&esdp->ssi->flags)
+		|| (erts_smp_atomic32_read_acqb(&esdp->ssi->flags)
 		    & ERTS_SSI_FLG_SUSPENDED)) {
 		ASSERT(erts_smp_atomic32_read(&esdp->ssi->flags)
 		       & ERTS_SSI_FLG_SUSPENDED);
 		suspend_scheduler(esdp);
 	    }
 	    if ((rq->flags & ERTS_RUNQ_FLG_CHK_CPU_BIND)
-		|| erts_smp_atomic32_read(&esdp->chk_cpu_bind)) {
+		|| erts_smp_atomic32_read_acqb(&esdp->chk_cpu_bind)) {
 		erts_sched_check_cpu_bind(esdp);
 	    }
 	}
@@ -5306,7 +5371,7 @@ Process *schedule(Process *p, int calls)
 	    if (rq->flags & (ERTS_RUNQ_FLG_SHARED_RUNQ
 			     | ERTS_RUNQ_FLG_SUSPENDED)) {
 		if ((rq->flags & ERTS_RUNQ_FLG_SUSPENDED)
-		    || (erts_smp_atomic32_read(&esdp->ssi->flags)
+		    || (erts_smp_atomic32_read_acqb(&esdp->ssi->flags)
 			& ERTS_SSI_FLG_SUSPENDED)) {
 		    ASSERT(erts_smp_atomic32_read(&esdp->ssi->flags)
 			   & ERTS_SSI_FLG_SUSPENDED);
@@ -5350,7 +5415,7 @@ Process *schedule(Process *p, int calls)
 	     * Schedule system-level activities.
 	     */
 
-	    erts_smp_atomic32_set(&function_calls, 0);
+	    erts_smp_atomic32_set_relb(&function_calls, 0);
 	    fcalls = 0;
 
 	    ASSERT(!erts_port_task_have_outstanding_io_tasks());
@@ -5392,7 +5457,7 @@ Process *schedule(Process *p, int calls)
 			if (erts_common_run_queue->waiting)
 			    wake_scheduler(erts_common_run_queue, 0, 1);
 		    }
-		    else if (erts_smp_atomic32_read(&no_empty_run_queues) != 0) {
+		    else if (erts_smp_atomic32_read_acqb(&no_empty_run_queues) != 0) {
 			wake_scheduler_on_empty_runq(rq);
 			rq->wakeup_other = 0;
 		    }