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From: Yafang Shao <laoar.shao@gmail.com>
Date: Tue, 19 Dec 2023 20:35:09 +0800
Message-ID: <CALOAHbDY0dkohOudFL4UAK2XBn0FKe7uKLmbWUzmDeEdTq8M9w@mail.gmail.com>
Subject: Re: [PATCH v1] sched/rt: Fix rt task's sched latency statistics in
 sched_stat_wait trace_point
To: Junwen Wu <wudaemon@163.com>
Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, 
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, 
	bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, 
	linux-kernel@vger.kernel.org
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On Mon, Dec 18, 2023 at 11:05=E2=80=AFPM Junwen Wu <wudaemon@163.com> wrote=
:
>
> When enable sched_stat_wait trace_point, some rt tasks sched latency
> so long, like this:
> sched_stat_wait: comm=3Drcu_preempt pid=3D14 delay=3D4936139545261 [ns]
> Rt task has low latency, it must have a bug. I found the reason is
> When rt task balance off source cpu, dequeue operation not update
> the sched_statistics, so follow update_stats_wait_end_fair
> update method.

Thanks for your report!

>
> Signed-off-by: Junwen Wu <wudaemon@163.com>
> ---
>  kernel/sched/rt.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 6aaf0a3d6081..c75215947c20 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1360,12 +1360,15 @@ update_stats_dequeue_rt(struct rt_rq *rt_rq, stru=
ct sched_rt_entity *rt_se,
>                         int flags)
>  {
>         struct task_struct *p =3D NULL;
> +       struct rq *rq =3D rq_of_rt_se(rt_se);
>
>         if (!schedstat_enabled())
>                 return;
>
>         if (rt_entity_is_task(rt_se))
>                 p =3D rt_task_of(rt_se);
> +       if (p !=3D rq->curr)

This seems wrong, the rt_se might not be a task.

I think we'd better use if (!on_rt_rq(rt_se))

> +               update_stats_wait_end_rt(rt_rq, rt_se);
>
>         if ((flags & DEQUEUE_SLEEP) && p) {
>                 unsigned int state;
> --
> 2.34.1
>


--
Regards
Yafang