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

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Message-ID: <20250521063705.GA4059166@bytedance>
Date: Wed, 21 May 2025 14:37:05 +0800
From: Aaron Lu <ziqianlu@...edance.com>
To: Florian Bezdeka <florian.bezdeka@...mens.com>
Cc: Valentin Schneider <vschneid@...hat.com>,
	Ben Segall <bsegall@...gle.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	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>
Subject: Re: [PATCH 2/7] sched/fair: prepare throttle path for task based
 throttle

On Tue, May 20, 2025 at 02:02:54PM +0200, Florian Bezdeka wrote:
> On Tue, 2025-05-20 at 18:41 +0800, Aaron Lu wrote:
> > @@ -6744,6 +6805,7 @@ static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq) { return false; }
> >  static void check_enqueue_throttle(struct cfs_rq *cfs_rq) {}
> >  static inline void sync_throttle(struct task_group *tg, int cpu) {}
> >  static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
> > +static void task_throttle_setup_work(struct task_struct *p) {}
> >  
> >  static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
> >  {
> > @@ -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 */
> 
> Typo: s/Shuold/Should
>

Ah right, thanks.

> Btw: Is there a trace point in place when throttling/unthrottling
> happens? Would be nice to see that in a trace, but might be that I
> missed those events in my configuration up to now.

There is no trace point for throttle related events yet.

I tried to see if bpftrace can do the job but unfortunately, bpftrace
does not allow variable as array indice so I failed to get cfs_rq when
probing tg_throttle_down(tg, data)...

Thanks,
Aaron

> > +		WARN_ON_ONCE(1);
> > +		task_throttle_setup_work(p);
> > +	}
> > +
> > +	return p;
> >  }
>