[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAKfTPtA3UTrsc3qZf_GB-QA7O7DJvoFqEk-VuWeFVRp8G_iUkg@mail.gmail.com>
Date: Wed, 17 Aug 2022 15:20:33 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Libo Chen <libo.chen@...cle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
juri.lelli@...hat.com, dietmar.eggemann@....com, mgorman@...e.de,
linux-kernel@...r.kernel.org,
Daniel Jordan <daniel.m.jordan@...cle.com>
Subject: Re: [PATCH 1/1] sched/fair: Fix inaccurate tally of ttwu_move_affine
On Mon, 15 Aug 2022 at 21:19, Libo Chen <libo.chen@...cle.com> wrote:
>
>
>
> 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@...cle.com>
> >> Signed-off-by: Libo Chen <libo.chen@...cle.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.
Looks good to me
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
>
>
> Libo
Powered by blists - more mailing lists