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

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Message-ID: <20250523073939.GA1038318@bytedance>
Date: Fri, 23 May 2025 15:40:14 +0800
From: Aaron Lu <ziqianlu@...edance.com>
To: Peter Zijlstra <peterz@...radead.org>
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 Thu, May 22, 2025 at 01:07:28PM +0200, Peter Zijlstra wrote:
> 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?
>

Ah yes.

> 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?

Thanks for the suggestion, will follow it in next version.