From: Peter Zijlstra peterz@infradead.org
[ Upstream commit 4c77b18cf8b7ab37c7d5737b4609010d2ceec5f0 ]
Kitsunyan reported desktop latency issues on his Celeron 887 because of commit:
1b568f0aabf2 ("sched/core: Optimize SCHED_SMT")
... even though his CPU doesn't do SMT.
The effect of running the SMT code on a !SMT part is basically a more aggressive select_idle_cpu(). Removing the avg condition fixed things for him.
I also know FB likes this test gone, even though other workloads like having it.
For now, take it out by default, until we get a better idea.
Reported-by: kitsunyan kitsunyan@inbox.ru Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: Chris Mason clm@fb.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Mike Galbraith efault@gmx.de Cc: Mike Galbraith umgwanakikbuti@gmail.com Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@verizon.com --- kernel/sched/fair.c | 2 +- kernel/sched/features.h | 5 +++++ 2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 7a68c631d5b5..3d862f5b0331 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5451,7 +5451,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t * Due to large variance we need a large fuzz factor; hackbench in * particularly is sensitive here. */ - if ((avg_idle / 512) < avg_cost) + if (sched_feat(SIS_AVG_CPU) && (avg_idle / 512) < avg_cost) return -1;
time = local_clock(); diff --git a/kernel/sched/features.h b/kernel/sched/features.h index 69631fa46c2f..1b3c8189b286 100644 --- a/kernel/sched/features.h +++ b/kernel/sched/features.h @@ -51,6 +51,11 @@ SCHED_FEAT(NONTASK_CAPACITY, true) */ SCHED_FEAT(TTWU_QUEUE, true)
+/* + * When doing wakeups, attempt to limit superfluous scans of the LLC domain. + */ +SCHED_FEAT(SIS_AVG_CPU, false) + #ifdef HAVE_RT_PUSH_IPI /* * In order to avoid a thundering herd attack of CPUs that are