linux-kernel - Re: [PATCH 2/6] sched/cpuset: Bring back cpuset

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Date:   Tue, 4 Apr 2023 13:31:51 -0400
From:   Waiman Long <longman@...hat.com>
To:     Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Qais Yousef <qyousef@...alina.io>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hao Luo <haoluo@...gle.com>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, luca.abeni@...tannapisa.it,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        bristot@...hat.com, mathieu.poirier@...aro.org,
        cgroups@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Wei Wang <wvw@...gle.com>, Rick Yiu <rickyiu@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH 2/6] sched/cpuset: Bring back cpuset_mutex

On 3/29/23 08:55, Juri Lelli wrote:
> Turns out percpu_cpuset_rwsem - commit 1243dc518c9d ("cgroup/cpuset:
> Convert cpuset_mutex to percpu_rwsem") - wasn't such a brilliant idea,
> as it has been reported to cause slowdowns in workloads that need to
> change cpuset configuration frequently and it is also not implementing
> priority inheritance (which causes troubles with realtime workloads).
>
> Convert percpu_cpuset_rwsem back to regular cpuset_mutex. Also grab it
> only for SCHED_DEADLINE tasks (other policies don't care about stable
> cpusets anyway).
>
> Signed-off-by: Juri Lelli <juri.lelli@...hat.com>

I am thinking that maybe we should switch the percpu rwsem to a regular 
rwsem as there are cases where a read lock is sufficient. This will also 
avoid the potential PREEMPT_RT problem with PI and reduce the time it 
needs to take a write lock.

Cheers,
Longman