Re: [PATCH 2/6] sched/cpuset: Bring back cpuset_mutex

Waiman Long
2023-04-26T14:05:49Z

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