linux-kernel - Re: [PATCH 2/7] sched/fair: prepare throttle path for task based throttle

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Message-ID: <20250522110728.GH39944@noisy.programming.kicks-ass.net>
Date: Thu, 22 May 2025 13:07:28 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Aaron Lu <ziqianlu@...edance.com>
Cc: Valentin Schneider <vschneid@...hat.com>,
	Ben Segall <bsegall@...gle.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Josh Don <joshdon@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Xi Wang <xii@...gle.com>, linux-kernel@...r.kernel.org,
	Juri Lelli <juri.lelli@...hat.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>, Mel Gorman <mgorman@...e.de>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	Chuyi Zhou <zhouchuyi@...edance.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Florian Bezdeka <florian.bezdeka@...mens.com>
Subject: Re: [PATCH 2/7] sched/fair: prepare throttle path for task based
 throttle

On Tue, May 20, 2025 at 06:41:05PM +0800, Aaron Lu wrote:
> @@ -8851,6 +8913,7 @@ static struct task_struct *pick_task_fair(struct rq *rq)
>  {
>  	struct sched_entity *se;
>  	struct cfs_rq *cfs_rq;
> +	struct task_struct *p;
>  
>  again:
>  	cfs_rq = &rq->cfs;
> @@ -8871,7 +8934,14 @@ static struct task_struct *pick_task_fair(struct rq *rq)
>  		cfs_rq = group_cfs_rq(se);
>  	} while (cfs_rq);
>  
> -	return task_of(se);
> +	p = task_of(se);
> +	if (throttled_hierarchy(cfs_rq_of(se))) {
> +		/* Shuold not happen for now */
> +		WARN_ON_ONCE(1);
> +		task_throttle_setup_work(p);
> +	}
> +
> +	return p;
>  }

So the final code is a little different, because you're removing the
return value from check_cfs_rq_runtime().

But would not that exact return value be the thing you're now checking
for again?

That is; at the end of the series, would not something like:

static struct task_struct *pick_task_fair(struct rq *rq)
{
	struct sched_entity *se;
	struct cfs_rq *cfs_rq;
	struct task_struct *p;
	bool throttled;

again:
	cfs_rq = &rq->cfs;
	if (!cfs_rq->nr_queued)
		return NULL;

	throttled = false;

	do {
		if (cfs_rq->curr && cfs_rq->curr->on_rq)
			update_curr(cfs_rq);

		throttled |= check_cfs_rq_runtime(cfs_rq);

		se = pick_next_entity(rq, cfs_rq);
		if (!se)
			goto again;

		cfs_rq = group_cfs_rq(se);
	} while (cfs_rq);

	p = task_of(se);
	if (unlikely(throttled))
		task_throttle_setup_work(p);
	return p;
}

make it more obvious / be simpler?