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From: Vincent Guittot <vincent.guittot@linaro.org>
To: Vincent Donnefort <Vincent.Donnefort@arm.com>
Cc: peterz@infradead.org, mingo@redhat.com,
	linux-kernel@vger.kernel.org, mgorman@techsingularity.net,
	dietmar.eggemann@arm.com, Valentin.Schneider@arm.com
Subject: Re: [PATCH] sched/fair: Fix per-CPU kthread and wakee stacking for asym CPU capacity
Date: Thu, 25 Nov 2021 10:10:01 +0100	[thread overview]
Message-ID: <CAKfTPtCrFoH-Kh0FAX_mWyjUymeHjCEOmJutL9qBpMftRe4Bdg@mail.gmail.com> (raw)
In-Reply-To: <20211124141435.3125147-1-vincent.donnefort@arm.com>

On Wed, 24 Nov 2021 at 15:15, Vincent Donnefort
<vincent.donnefort@arm.com> wrote:
>
> A shortcut has been introduced in select_idle_sibling() to return prev_cpu
> if the wakee is woken up by a per-CPU kthread. This is an issue for
> asymmetric CPU capacity systems where the wakee might not fit prev_cpu
> anymore. Evaluate asym_fits_capacity() for prev_cpu before using that
> shortcut.
>
> Fixes: 52262ee567ad ("sched/fair: Allow a per-CPU kthread waking a task to stack on the same CPU, to fix XFS performance regression")
> Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com>
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 6291876a9d32..b90dc6fd86ca 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6410,7 +6410,8 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>          */
>         if (is_per_cpu_kthread(current) &&
>             prev == smp_processor_id() &&
> -           this_rq()->nr_running <= 1) {
> +           this_rq()->nr_running <= 1 &&
> +           asym_fits_capacity(task_util, prev)) {

With this patch, i don't think that
20211124154239.3191366-1-vincent.donnefort@arm.com is needed anymore

>                 return prev;
>         }
>
> --
> 2.25.1
>

      parent reply	other threads:[~2021-11-25  9:18 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-24 14:14 Vincent Donnefort
2021-11-24 17:11 ` Valentin Schneider
2021-11-24 17:58   ` Vincent Donnefort
2021-11-24 18:04     ` Valentin Schneider
2021-11-25  9:10 ` Vincent Guittot [this message]

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