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

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Message-ID: <58e0515a-ed67-4d1a-825f-bfc2b31d1d18@linux.dev>
Date: Fri, 14 Mar 2025 16:39:41 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Aaron Lu <ziqianlu@...edance.com>,
 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>
Cc: 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>
Subject: Re: [RFC PATCH 2/7] sched/fair: Handle throttle path for task based
 throttle

On 2025/3/13 15:21, Aaron Lu wrote:
> From: Valentin Schneider <vschneid@...hat.com>
> 
> Once a cfs_rq gets throttled, for all tasks belonging to this cfs_rq,
> add a task work to them so that when those tasks return to user, the
> actual throttle/dequeue can happen.
> 
> Note that since the throttle/dequeue always happens on a task basis when
> it returns to user, it's no longer necessary for check_cfs_rq_runtime()
> to return a value and pick_task_fair() acts differently according to that
> return value, so check_cfs_rq_runtime() is changed to not return a
> value.

Previously with the per-cfs_rq throttling, we use update_curr() -> put() path
to throttle the cfs_rq and dequeue it from the cfs_rq tree.

Now with your per-task throttling, maybe things can become simpler. That we
can just throttle_cfs_rq() (cfs_rq subtree) when curr accouting to mark these
throttled.

Then then if we pick a task from a throttled cfs_rq subtree, we can setup task work
for it, so we don't botter with the delayed_dequeue task case that Prateek mentioned.

WDYT?

Thanks.