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

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Message-ID: <20250905075338.GK42@bytedance>
Date: Fri, 5 Sep 2025 15:53:38 +0800
From: Aaron Lu <ziqianlu@...edance.com>
To: Benjamin Segall <bsegall@...gle.com>
Cc: K Prateek Nayak <kprateek.nayak@....com>,
	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

On Thu, Sep 04, 2025 at 08:04:01PM +0800, Aaron Lu wrote:
... ...
> Per my understanding, we keep PELT clock running because we want the
> throttled cfs_rq's load to continue get update when it still has tasks
> running in kernel mode and have that up2date load could let it have a
> hopefully more accurate weight through update_cfs_group(). So it looks
> to me, if PELT clock should not be stopped, then we should not abort in
> propagate_entity_cfs_rq() and update_cfs_group(). I missed these two
> aborts in these two functions, but now you and Peter have pointed this
> out, I suppose there is no doubt we should not abort in
> update_cfs_group() and propagate_entity_cfs_rq()? If we should not mess
> with shares distribution, then the up2date load is not useful and why
> not simply freeze PELT clock on throttle :)

With more thinking, when PELT clock is running, root level cfs_rq's load
can be updated and that is useful for things like load balance.

update_cfs_group() is a different story and as Ben said, there is cons
and pros whether to abort there for throttled cfs_rq so there's no
obvious thing to do for it.