linux-kernel - Re: [PATCH v4 3/5] sched/fair: Switch to task based throttle model

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Message-ID: <da9141b1-d717-493f-939f-85e23d46e7ba@amd.com>
Date: Thu, 4 Sep 2025 15:21:06 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Aaron Lu <ziqianlu@...edance.com>, Benjamin Segall <bsegall@...gle.com>
CC: Peter Zijlstra <peterz@...radead.org>, Valentin Schneider
	<vschneid@...hat.com>, Chengming Zhou <chengming.zhou@...ux.dev>, 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>, Chuyi Zhou <zhouchuyi@...edance.com>, "Jan
 Kiszka" <jan.kiszka@...mens.com>, Florian Bezdeka
	<florian.bezdeka@...mens.com>, Songtang Liu <liusongtang@...edance.com>,
	"Chen Yu" <yu.c.chen@...el.com>, Matteo Martelli
	<matteo.martelli@...ethink.co.uk>, Michal Koutn?? <mkoutny@...e.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH v4 3/5] sched/fair: Switch to task based throttle model

Hello Aaron,

On 9/4/2025 1:46 PM, Aaron Lu wrote:
> @@ -8722,15 +8730,6 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
>  	if (unlikely(se == pse))
>  		return;
>  
> -	/*
> -	 * This is possible from callers such as attach_tasks(), in which we
> -	 * unconditionally wakeup_preempt() after an enqueue (which may have
> -	 * lead to a throttle).  This both saves work and prevents false
> -	 * next-buddy nomination below.
> -	 */
> -	if (unlikely(throttled_hierarchy(cfs_rq_of(pse))))
> -		return;

I think we should have a:

	if (task_is_throttled(p))
		return;

here. I can see at least one possibility via prio_changed_fair()
where a throttled task might reach here. Rest looks good. I'll
still wait on Ben for the update_cfs_group() bits :)

> -
>  	if (sched_feat(NEXT_BUDDY) && !(wake_flags & WF_FORK) && !pse->sched_delayed) {
>  		set_next_buddy(pse);
>  	}
-- 
Thanks and Regards,
Prateek