linux-kernel - Re: [PATCH] [RFC] sched: Add trace_sched_waking() tracepoint to sched_ttwu

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Date: Thu, 22 Feb 2024 16:24:09 -0500
From: Phil Auld <pauld@...hat.com>
To: John Stultz <jstultz@...gle.com>
Cc: LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>, kernel-team@...roid.com,
	Zimuzo Ezeozue <zezeozue@...gle.com>
Subject: Re: [PATCH] [RFC] sched: Add trace_sched_waking() tracepoint to
 sched_ttwu_pending()

On Thu, Feb 22, 2024 at 12:49:03PM -0800 John Stultz wrote:
> Zimuzo reported seeing occasional cases in perfetto traces where
> tasks went from sleeping directly to trace_sched_wakeup()
> without always seeing a trace_sched_waking().
> 
> Looking at the code, trace_sched_wakeup() is only called in
> ttwu_do_wakeup()
> 
> The call paths that get you to ttwu_do_wakeup() are:
> try_to_wake_up() -> ttwu_do_wakeup()
> try_to_wake_up() -> ttwu_runnable() -> ttwu_do_wakeup()
> try_to_wake_up() -> ttwu_queue() -> ttwu_do_activate() -> ttwu_do_wakeup()
> sched_ttwu_pending() -> ttwu_do_activate() -> ttwu_do_wakeup()
> 
> where trace_sched_waking() is currently called only in
> try_to_wake_up().
> 
> So this patch adds a trace_sched_waking() call to
> sched_ttwu_pending(), so we see the same state machine
> transitions.
> 
> With this change, the number of unexpected state transitions
> in perfetto was greatly reduced.
> 
> This has been in my drafts for awhile, so I wanted to send
> this out for thoughts/feedback.
> 
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Juri Lelli <juri.lelli@...hat.com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Cc: kernel-team@...roid.com
> Reported-by: Zimuzo Ezeozue <zezeozue@...gle.com>
> Signed-off-by: John Stultz <jstultz@...gle.com>
> ---
>  kernel/sched/core.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 9116bcc90346..233f06360d6a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3894,6 +3894,7 @@ void sched_ttwu_pending(void *arg)
>  		if (WARN_ON_ONCE(task_cpu(p) != cpu_of(rq)))
>  			set_task_cpu(p, cpu_of(rq));
>  
> +		trace_sched_waking(p);
>  		ttwu_do_activate(rq, p, p->sched_remote_wakeup ? WF_MIGRATED : 0, &rf);
>  	}
>  
> -- 
> 2.44.0.rc0.258.g7320e95886-goog
> 
> 

This looks okay to me.

Maybe s/this patch adds/add/. Otherwise the changelog is nice and
complete.

Reviewed-by: Phil Auld <pauld@...hat.com>

Cheers,
Phil
--