4.9-stable review patch. If anyone has any objections, please let me know.
------------------ 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]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- kernel/sched/fair.c | 2 +- kernel/sched/features.h | 5 +++++ 2 files changed, 6 insertions(+), 1 deletion(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5451,7 +5451,7 @@ static int select_idle_cpu(struct task_s * 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(); --- 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
