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Date:   Thu, 3 Nov 2022 11:11:24 +0100
From:   Michal =?iso-8859-1?Q?Koutn=FD?= <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
Message-ID: <20221103101124.GD10591@blackbody.suse.cz>
References: <20221026224449.214839-1-joshdon@google.com>
 <20221102165922.GA31833@blackbody.suse.cz>
 <CABk29Nsjbex9VYw01HQN4Bgvrf66w2YDfpRLuns2nDt5UxCjUg@mail.gmail.com>
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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


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