linux-kernel - Re: [PATCH v4] sched/stats: Fix rt/dl task's sched latency statistics error in sched_stat_wait trace

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Message-ID: <CALOAHbAtXQsqi5ny58NRG9wOmZpOVkCi7yyy-ZtZdTnHZcPz5g@mail.gmail.com>
Date: Thu, 11 Jan 2024 19:52:30 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: Junwen Wu <wudaemon@....com>
Cc: bristot@...hat.com, mingo@...hat.com, peterz@...radead.org, 
	juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com, 
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] sched/stats: Fix rt/dl task's sched latency statistics
 error in sched_stat_wait trace_point

On Wed, Jan 10, 2024 at 9:32 PM Junwen Wu <wudaemon@....com> wrote:
>
> The sched_stat_wait tracepoint is showing unreasonably long
> latencies for real-time tasks. For example:
>
> sched_stat_wait: comm=rcu_preempt pid=14 delay=4936139545261 [ns]
>
> This error happens when the rt task balances off the source CPU because
> the dequeue operation is not updating the sched_statistics. So, follow
> update_stats_wait_end_fair() and update the stats. Do the same for
> SCHED_DEADLINE.
>
> 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>

BTW, feel free to include the 'acked-by' in a newer version if your
modifications are only minor.

> ---
>  kernel/sched/deadline.c | 5 ++++-
>  kernel/sched/rt.c       | 4 ++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index b28114478b82..4a9aad291fb9 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1558,10 +1558,13 @@ 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..5cb3a54d6b13 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1360,12 +1360,16 @@ 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;
> --
> 2.34.1
>


-- 
Regards
Yafang