From: Peter Zijlstra <[email protected]>
[ 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 <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
---
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
--
2.11.0
