Re: [PATCH v2] sched: async unthrottling for cfs bandwidth

From: "Michal Koutný" <mkoutny@suse.com>
To: Josh Don <joshdon@google.com>
Cc: Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Valentin Schneider <vschneid@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] sched: async unthrottling for cfs bandwidth
Date: Thu, 3 Nov 2022 11:11:24 +0100	[thread overview]
Message-ID: <20221103101124.GD10591@blackbody.suse.cz> (raw)
In-Reply-To: <CABk29Nsjbex9VYw01HQN4Bgvrf66w2YDfpRLuns2nDt5UxCjUg@mail.gmail.com>

[-- Attachment #1: Type: text/plain, Size: 812 bytes --]

On Wed, Nov 02, 2022 at 05:10:08PM -0700, Josh Don <joshdon@google.com> wrote:
> Without my patch, distribute_cfs_runtime() will unthrottle the
> cfs_rq's, and as you point out, it doesn't actually give them any real
> quota, it lets assign_cfs_rq_runtime() take care of that. But this
> happens asynchronously on those cpus. If they are idle, they wait for
> an IPI from the resched_curr() in unthrottled_cfs_rq(), otherwise they
> simply wait until potentially the next rescheduling point. So we are
> currently far from ever being guaranteed that the order the cpus pull
> actual quota via assign_cfs_rq_runtime() matches the order they were
> unthrottled from the list.

Thanks for breaking it down, I agree your change won't affect the
fairness substantially and my other points are clarified too.

Michal

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 228 bytes --]