linux-kernel - Re: [PATCH 1/5] cgroup/cpuset: Skip task update if hotplug doesn't affect current cpuset

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Date:   Tue, 14 Mar 2023 14:20:53 -0400
From:   Waiman Long <longman@...hat.com>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shuah Khan <shuah@...nel.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/5] cgroup/cpuset: Skip task update if hotplug doesn't
 affect current cpuset


On 3/14/23 12:50, Michal Koutný wrote:
> On Mon, Mar 06, 2023 at 03:08:45PM -0500, Waiman Long <longman@...hat.com> wrote:
>> If a hotplug event doesn't affect the current cpuset, there is no point
>> to call hotplug_update_tasks() or hotplug_update_tasks_legacy(). So
>> just skip it.
> This skips "insane" modification of cs->cpus_allowed in
> hotplug_update_tasks_legacy() but assuming cs->cpus_allowed is kept in
> sync with cs->effective_cpus on v1, it is OK to skip the update based
> only on effective_cpus check.

Yes, effective_cpus is equivalent to cpus_allowed in v1 unless you mount 
the cpuset with the cpuset_v2_mode flag which will behave more like v2 
where effective_cpus is still the key.

Cheers,
Longman