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Sender: Tejun Heo <htejun@gmail.com>
Date:   Tue, 1 Nov 2022 09:15:33 -1000
From:   Tejun Heo <tj@kernel.org>
To:     Josh Don <joshdon@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        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,
        Joel Fernandes <joel@joelfernandes.org>
Subject: Re: [PATCH v2] sched: async unthrottling for cfs bandwidth
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Hello,

On Tue, Nov 01, 2022 at 12:11:30PM -0700, Josh Don wrote:
> > Just to better understand the situation, can you give some more details on
> > the scenarios where cgroup_mutex was in the middle of a shitshow?
> 
> There have been a couple, I think one of the main ones has been writes
> to cgroup.procs. cpuset modifications also show up since there's a
> mutex there.

If you can, I'd really like to learn more about the details. We've had some
issues with the threadgroup_rwsem because it's such a big hammer but not
necessarily with cgroup_mutex because they are only used in maintenance
operations and never from any hot paths.

Regarding threadgroup_rwsem, w/ CLONE_INTO_CGROUP (userspace support is
still missing unfortunately), the usual worfklow of creating a cgroup,
seeding it with a process and then later shutting it down doesn't involve
threadgroup_rwsem at all, so most of the problems should go away in the
hopefully near future.

Thanks.

-- 
tejun