linux-kernel - Re: [RFC PATCH] sched/fair: Fixup wake_up_sync vs DELAYED

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Message-ID: <CAKfTPtBB6FH+5G5eRxC-0UA3H_M6Qt=CvKfCNvHy2=Dg0EEMxw@mail.gmail.com>
Date: Fri, 28 Feb 2025 17:39:26 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Xuewen Yan <xuewen.yan@...soc.com>
Cc: peterz@...radead.org, mingo@...hat.com, juri.lelli@...hat.com, 
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, 
	mgorman@...e.de, vschneid@...hat.com, ke.wang@...soc.com, di.shen@...soc.com, 
	xuewen.yan94@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] sched/fair: Fixup wake_up_sync vs DELAYED_DEQUEUE

On Wed, 26 Feb 2025 at 03:51, Xuewen Yan <xuewen.yan@...soc.com> wrote:
>
> Delayed dequeued feature keeps a sleeping task enqueued until its
> lag has elapsed. As a result, it stays also visible in rq->nr_running.
> So when in ake_affine_idle(), we should use the real running-tasks

typo: wake_affine_idle

> in rq to check whether we should place the wake-up task to
> current cpu.

fair enough

>
> Fixes: 152e11f6df29 ("sched/fair: Implement delayed dequeue")
> Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
> ---
>  kernel/sched/fair.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1c0ef435a7aa..2d6d5582c3e9 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7342,8 +7342,15 @@ wake_affine_idle(int this_cpu, int prev_cpu, int sync)
>         if (available_idle_cpu(this_cpu) && cpus_share_cache(this_cpu, prev_cpu))
>                 return available_idle_cpu(prev_cpu) ? prev_cpu : this_cpu;
>
> -       if (sync && cpu_rq(this_cpu)->nr_running == 1)
> -               return this_cpu;
> +       if (sync) {
> +               struct rq *rq = cpu_rq(this_cpu);
> +               int nr_delayed;
> +
> +               nr_delayed = rq->cfs.h_nr_queued - rq->cfs.h_nr_runnable;

Could you encapsulate this in a helper function ? something like below

static inline unsigned int cfs_h_nr_delayed(struct rq *rq)
{
        struct rq *rq = cpu_rq(this_cpu);

        return (rq->cfs.h_nr_queued - rq->cfs.h_nr_runnable);
}

> +
> +               if ((rq->nr_running - nr_delayed) == 1)
> +                       return this_cpu;
> +       }
>
>         if (available_idle_cpu(prev_cpu))
>                 return prev_cpu;
> --
> 2.25.1
>
>