linux-kernel - Re: [PATCH] sched/fair: Prevent cfs_rq from being unthrottled with zero runtime

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Message-ID: <20251001115842.GA674@bytedance>
Date: Wed, 1 Oct 2025 19:58:42 +0800
From: Aaron Lu <ziqianlu@...edance.com>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: Valentin Schneider <vschneid@...hat.com>,
	Ben Segall <bsegall@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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 Koutný <mkoutny@...e.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH] sched/fair: Prevent cfs_rq from being unthrottled with
 zero runtime_remaining

On Tue, Sep 30, 2025 at 07:08:20PM +0530, K Prateek Nayak wrote:
> Hello Aaron,
> 
> I'll merge the two replies in one.
> 
> On 9/30/2025 4:37 PM, Aaron Lu wrote:
> > So in my original patch, cfs_rqs will (most likely) start with
> > runtime_remaining == 1 and unthrottled after calling throttle_cfs_rq(),
> > which will also start the B/W timer. The timer is not needed in this
> > case when no cfs_rqs are actually throttled but it doesn't hurt. Looks
> > like everything is OK, we do not need to do any special handling in
> > enqueue_throttled_task(). Thoughts?
> 
> Now that I look at throttle_cfs_rq() properly, we'll only move the
> runtime_remaining from 0 to 1 so few usecs worth of bandwidth
> distributed at max should be okay. Sorry for the being overly cautious!

Never mind.

> 
> So your current approach should be good. Please feel free to include:
> 
> Reviewed-by: K Prateek Nayak <kprateek.nayak@....com>

Thanks!