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

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Message-ID: <20221102171049.GC10591@blackbody.suse.cz>
Date:   Wed, 2 Nov 2022 18:10:49 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Josh Don <joshdon@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        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,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <brauner@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>
Subject: Re: [PATCH v2] sched: async unthrottling for cfs bandwidth

On Tue, Nov 01, 2022 at 12:38:23PM -1000, Tejun Heo <tj@...nel.org> wrote:
> (cc'ing Michal, Christian and Li for context)

Thanks.

> > We're in the process of transitioning to using bw instead for this
> > instead in order to maintain parallelism. Fixing bw is definitely
> > going to be useful, but I'm afraid we'll still likely have some issues
> > from low throughput for non-bw reasons (some of which we can't
> > directly control, since arbitrary jobs can spin up and configure their
> > hierarchy/threads in antagonistic ways, in effect pushing out the
> > latency of some of their threads).
> 
> Yeah, thanks for the explanation. Making the lock more granular is tedious
> but definitely doable. I don't think I can work on it in the near future but
> will keep it on mind. If anyone's interested in attacking it, please be my
> guest.

From my experience, throttling while holding kernel locks (not just
cgroup_mutex) causes more trouble than plain cgroup_mutex scalability
currently.
But I acknowledge the latter issue too.

Michal

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