Messages in this thread | | | Date | Thu, 25 Aug 2022 13:00:03 +0530 | From | "Gautham R. Shenoy" <> | Subject | Re: [PATCH 1/1] sched/fair: Fix inaccurate tally of ttwu_move_affine |
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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;
This seems to be the right thing to do. However,..
if this_cpu and prev_cpu were in the same LLC and we pick prev_cpu, technically is it still not an affine wakeup?
> > schedstat_inc(sd->ttwu_move_affine); > -- > 2.31.1 >
-- Thanks and Regards gautham.
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