linux-kernel - Re: [PATCH v2] sched/rt: Fix rt task's sched latency statistics error in sched_stat_wait trace

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Date: Sun, 24 Dec 2023 19:38:25 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: Junwen Wu <wudaemon@....com>
Cc: bristot@...hat.com, bsegall@...gle.com, dietmar.eggemann@....com, 
	juri.lelli@...hat.com, linux-kernel@...r.kernel.org, mgorman@...e.de, 
	mingo@...hat.com, peterz@...radead.org, rostedt@...dmis.org, 
	vincent.guittot@...aro.org, vschneid@...hat.com
Subject: Re: [PATCH v2] sched/rt: Fix rt task's sched latency statistics error
 in sched_stat_wait trace_point

On Sat, Dec 23, 2023 at 1:38 PM Junwen Wu <wudaemon@....com> wrote:
>
> >It seems DL has the same issue. Pls. also fix it in update_stats_dequeue_dl().
> >And add the Fixes tag in the commit log:
> >Fixes: 57a5c2dafca8 ("sched/rt: Support schedstats for RT sched class")
> >Fixes: b5eb4a5f6521 ("sched/dl: Support schedstats for deadline sched class")
>
> ok, the PATCH v3 below is ok?
>
> Subject: [PATCH v3] sched/stats: Fix rt/dl task's sched latency statistics
>  error in sched_stat_wait trace_point
>
> When enable sched_stat_wait trace_point, some rt tasks sched latency so long, like this,
> sched_stat_wait: comm=rcu_preempt pid=14 delay=4936139545261 [ns]
> Rt task has low latency, it must have a bug. When rt task balance off source cpu,
> dequeue operation not update the sched_statistics, so follow update_stats_wait_end_fair
> update method, so do dl tasks.
>
> Fixes: 57a5c2dafca8 ("sched/rt: Support schedstats for RT sched class")
> Fixes: b5eb4a5f6521 ("sched/dl: Support schedstats for deadline sched class")
> Signed-off-by: Junwen Wu <wudaemon@....com>

Acked-by: Yafang Shao <laoar.shao@...il.com>

> ---
>  kernel/sched/deadline.c | 8 +++++++-
>  kernel/sched/rt.c       | 7 +++++++
>  2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index b28114478b82..29223163ee22 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1558,10 +1558,16 @@ update_stats_dequeue_dl(struct dl_rq *dl_rq, struct sched_dl_entity *dl_se,
>                         int flags)
>  {
>         struct task_struct *p = dl_task_of(dl_se);
> +       struct rq *rq = rq_of_dl_rq(dl_rq);
>
>         if (!schedstat_enabled())
>                 return;
> -
> +       /*
> +        * Mark the end of the wait period
> +        * if dequeueing a waiting task.
> +        */
> +       if (p && (p != rq->curr))
> +                update_stats_wait_end_dl(dl_rq, dl_se);
>         if ((flags & DEQUEUE_SLEEP)) {
>                 unsigned int state;
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 6aaf0a3d6081..6a2600213991 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1360,12 +1360,19 @@ update_stats_dequeue_rt(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se,
>                         int flags)
>  {
>         struct task_struct *p = NULL;
> +       struct rq *rq = rq_of_rt_se(rt_se);
>
>         if (!schedstat_enabled())
>                 return;
>
>         if (rt_entity_is_task(rt_se))
>                 p = rt_task_of(rt_se);
> +        /*
> +         * Mark the end of the wait period
> +         * if dequeueing a waiting task.
> +         */
> +       if (p && (p != rq->curr))
> +               update_stats_wait_end_rt(rt_rq, rt_se);
>
>         if ((flags & DEQUEUE_SLEEP) && p) {
>                 unsigned int state;
>
> --
> Best regards
>


-- 
Regards
Yafang