linux-kernel - Re: [PATCH 1/1] sched/fair: Fix inaccurate tally of ttwu_move

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

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