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

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Message-ID: <ddd2f979-43d5-43e8-a95c-37a1654189e5@amd.com>
Date: Thu, 4 Sep 2025 11:14:31 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Peter Zijlstra <peterz@...radead.org>
CC: Aaron Lu <ziqianlu@...edance.com>, Valentin Schneider
	<vschneid@...hat.com>, Ben Segall <bsegall@...gle.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 9/4/2025 1:57 AM, Peter Zijlstra wrote:
> So this is mostly tasks leaving/joining the class/cgroup. And its
> purpose seems to be to remove/add the blocked load component.
> 
> Previously throttle/unthrottle would {de,en}queue the whole subtree from
> PELT, see how {en,de}queue would also stop at throttle.
> 
> But now none of that is done; PELT is fully managed by the tasks
> {de,en}queueing.
> 
> So I'm thinking that when a task joins fair (deboost from RT or
> whatever), we add the blocking load and fully propagate it. If the task
> is subject to throttling, that will then happen 'naturally' and it will
> dequeue itself again.

That seems like the correct thing to do yes. Those throttled_cfs_rq()
checks in propagate_entity_cfs_rq() can be removed then.

-- 
Thanks and Regards,
Prateek