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

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Message-ID: <CABk29Nvw8XMrc2_9CAUZb=rO_vddGjsfZ1s3mRQyShANDhtZnw@mail.gmail.com>
Date:   Tue, 15 Nov 2022 19:01:31 -0800
From:   Josh Don <joshdon@...gle.com>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched: async unthrottling for cfs bandwidth

On Wed, Nov 2, 2022 at 9:59 AM Michal Koutný <mkoutny@...e.com> wrote:
>
> Also, can a particular cfs_rq be on both cfs_b->throttled_csd_list and
> cfs_b->throttled_cfs_rq lists at any moment?
> I wonder if having a single list_head node in cfs_rq would be feasible
> (and hence enforcing this constraint in data).

After more thought, I realized that we can't reuse the throttled_list
list_head, since that would potentially break the lockless traversal
of a concurrent list_for_each_entry_rcu() (ie. if we removed the
element from the throttled list and then added it to the CSD list).

- Josh