Messages in this thread | | | Date | Mon, 15 Aug 2022 12:19:01 -0700 | Subject | Re: [PATCH 1/1] sched/fair: Fix inaccurate tally of ttwu_move_affine | From | Libo Chen <> |
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On 8/15/22 04:01, Peter Zijlstra wrote: > On Wed, Aug 10, 2022 at 03:33:13PM -0700, Libo Chen wrote: >> There are scenarios where non-affine wakeups are incorrectly counted as >> affine wakeups by schedstats. >> >> When wake_affine_idle() returns prev_cpu which doesn't equal to >> nr_cpumask_bits, it will slip through the check: target == nr_cpumask_bits >> in wake_affine() and be counted as if target == this_cpu in schedstats. >> >> Replace target == nr_cpumask_bits with target != this_cpu to make sure >> affine wakeups are accurately tallied. >> >> Fixes: 806486c377e33 (sched/fair: Do not migrate if the prev_cpu is idle) >> Suggested-by: Daniel Jordan <daniel.m.jordan@oracle.com> >> Signed-off-by: Libo Chen <libo.chen@oracle.com> >> --- >> kernel/sched/fair.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index da388657d5ac..b179da4f8105 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -6114,7 +6114,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, >> target = wake_affine_weight(sd, p, this_cpu, prev_cpu, sync); >> >> schedstat_inc(p->stats.nr_wakeups_affine_attempts); >> - if (target == nr_cpumask_bits) >> + if (target != this_cpu) >> return prev_cpu; >> >> schedstat_inc(sd->ttwu_move_affine); > This not only changes the accounting but also the placement, no? No, it should only change the accounting. wake_affine() still returns prev_cpu if target equals to prev_cpu or nr_cpumask_bits, the same behavior as before.
Libo
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