linux-kernel - Re: [PATCH 4/5] sched: Add rt task enqueue/dequeue trace points

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Message-ID: <5a7c492bbad7d56f347ee629734fdbab275d6333.camel@redhat.com>
Date: Thu, 31 Jul 2025 10:39:25 +0200
From: Gabriele Monaco <gmonaco@...hat.com>
To: Nam Cao <namcao@...utronix.de>
Cc: Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>,  Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 linux-trace-kernel@...r.kernel.org, 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>,
 Ben Segall	 <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, Valentin
 Schneider	 <vschneid@...hat.com>
Subject: Re: [PATCH 4/5] sched: Add rt task enqueue/dequeue trace points

On Thu, 2025-07-31 at 09:35 +0200, Nam Cao wrote:
> On Wed, Jul 30, 2025 at 06:18:45PM +0200, Gabriele Monaco wrote:
> > Well, thinking about it again, these tracepoints might simplify
> > things
> > considerably when tasks change policy..
> > 
> > Syscalls may fail, for that you could register to sys_exit and
> > check
> > the return value, but at that point the policy changed already, so
> > you
> > cannot tell if it's a relevant event or not (e.g. same policy).
> > Also sched_setscheduler_nocheck would be out of the picture here,
> > not
> > sure how recurrent that is though (and might not matter if you only
> > focus on userspace tasks).
> > 
> > If you go down the route of adding tracepoints, why not have other
> > classes benefit too? I believe calling them from the enqueue_task /
> > dequeue_task in sched/core.c would allow you to easily filter out
> > by
> > policy anyway (haven't tested).
> 
> Something like the untested patch below?
> 
> Will you have a use case for it too? Then I will try to accommodate
> your use case, otherwise I will do just enough for my case.

Well, I'm still defining the best set of tracepoints I need, if you see
it cleaner go ahead the way you're currently doing, then.
Unless anyone else complains let's keep it like this.

Thanks,
Gabriele

> 
> Nam
> 
> diff --git a/include/trace/events/sched.h
> b/include/trace/events/sched.h
> index c38f12f7f903..b50668052f99 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -906,6 +906,14 @@ DECLARE_TRACE(dequeue_task_rt,
>  	TP_PROTO(int cpu, struct task_struct *task),
>  	TP_ARGS(cpu, task));
>  
> +DECLARE_TRACE(enqueue_task,
> +	TP_PROTO(int cpu, struct task_struct *task),
> +	TP_ARGS(cpu, task));
> +
> +DECLARE_TRACE(dequeue_task,
> +	TP_PROTO(int cpu, struct task_struct *task),
> +	TP_ARGS(cpu, task));
> +
>  #endif /* _TRACE_SCHED_H */
>  
>  /* This part must be outside protection */
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index b485e0639616..2af90532982a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2077,6 +2077,8 @@ unsigned long get_wchan(struct task_struct *p)
>  
>  void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
>  {
> +	trace_enqueue_task_tp(rq->cpu, p);
> +
>  	if (!(flags & ENQUEUE_NOCLOCK))
>  		update_rq_clock(rq);
>  
> @@ -2103,6 +2105,8 @@ void enqueue_task(struct rq *rq, struct
> task_struct *p, int flags)
>   */
>  inline bool dequeue_task(struct rq *rq, struct task_struct *p, int
> flags)
>  {
> +	trace_dequeue_task_tp(rq->cpu, p);
> +
>  	if (sched_core_enabled(rq))
>  		sched_core_dequeue(rq, p, flags);
>