From mboxrd@z Thu Jan  1 00:00:00 1970
From: Waiman Long <longman@redhat.com>
Subject: Re: [PATCH 2/6] sched/cpuset: Bring back cpuset_mutex
Date: Wed, 26 Apr 2023 10:05:49 -0400
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To: Juri Lelli <juri.lelli@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>, Qais Yousef <qyousef@layalina.io>, Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>, Johannes Weiner <hannes@cmpxchg.org>, Hao Luo <haoluo@google.com>, Dietmar Eggemann <dietmar.eggemann@arm.com>, Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org, luca.abeni@santannapisa.it, claudio@evidence.eu.com, tommaso.cucinotta@santannapisa.it, bristot@redhat.com, mathieu.poirier@linaro.org, cgroups@vger.kernel.org, Vincent Guittot <vincent.guittot@linaro.org>, Wei Wang <wvw@google.com>, Rick Yiu <rickyiu@google.com>, Quentin Perret <qperret@google.com>, Heiko Carstens <hca@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, Alexander Gordeev <agordeev@linux.ibm.>

On 4/26/23 07:57, Juri Lelli wrote:
> On 04/04/23 13:31, Waiman Long wrote:
>> 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@redhat.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.
> I'm not a big fan of rwsems for reasons like
> https://lore.kernel.org/lkml/20230321161140.HMcQEhHb@linutronix.de/, so
> I'd vote for a standard mutex unless we have a strong argument and/or
> numbers.

That is fine for me too.

Cheers,
Longman