[PATCH] sched: disable sync wakeups

[Peter Zijlstra]

Pawel Dziekonski reported that the openssl benchmark and his
quantum chemistry application both show slowdowns due to the
scheduler under-parallelizing execution.

The reason are pipe wakeups still doing 'sync' wakeups which
overrides the normal buddy wakeup logic - even if waker and
wakee are loosely coupled.

So disable sync wakeups and also fix an inversion of logic
in the buddy wakeup code.

Reported-by: Pawel Dziekonski <dzieko@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 kernel/sched.c          |    4 ++++
 kernel/sched_fair.c     |    8 +-------
 kernel/sched_features.h |    2 +-
 3 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 8c2be1e..ce1cfc6 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2266,6 +2266,10 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
 	if (!sched_feat(SYNC_WAKEUPS))
 		sync = 0;
 
+	if (!sync && (current->se.avg_overlap < sysctl_sched_migration_cost &&
+			    p->se.avg_overlap < sysctl_sched_migration_cost))
+		sync = 1;
+
 #ifdef CONFIG_SMP
 	if (sched_feat(LB_WAKEUP_UPDATE)) {
 		struct sched_domain *sd;
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 5cc1c16..fd789a2 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1189,10 +1189,6 @@ wake_affine(struct sched_domain *this_sd, struct rq *this_rq,
 	if (!(this_sd->flags & SD_WAKE_AFFINE) || !sched_feat(AFFINE_WAKEUPS))
 		return 0;
 
-	if (sync && (curr->se.avg_overlap > sysctl_sched_migration_cost ||
-			p->se.avg_overlap > sysctl_sched_migration_cost))
-		sync = 0;
-
 	/*
 	 * If sync wakeup then subtract the (maximum possible)
 	 * effect of the currently running task from the load
@@ -1419,9 +1415,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int sync)
 	if (!sched_feat(WAKEUP_PREEMPT))
 		return;
 
-	if (sched_feat(WAKEUP_OVERLAP) && (sync ||
-			(se->avg_overlap < sysctl_sched_migration_cost &&
-			 pse->avg_overlap < sysctl_sched_migration_cost))) {
+	if (sched_feat(WAKEUP_OVERLAP) && sync) {
 		resched_task(curr);
 		return;
 	}
diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index da5d93b..8134e65 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -4,7 +4,7 @@ SCHED_FEAT(WAKEUP_PREEMPT, 1)
 SCHED_FEAT(START_DEBIT, 1)
 SCHED_FEAT(AFFINE_WAKEUPS, 1)
 SCHED_FEAT(CACHE_HOT_BUDDY, 1)
-SCHED_FEAT(SYNC_WAKEUPS, 1)
+SCHED_FEAT(SYNC_WAKEUPS, 0)
 SCHED_FEAT(HRTICK, 0)
 SCHED_FEAT(DOUBLE_TICK, 0)
 SCHED_FEAT(ASYM_GRAN, 1)
--
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