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

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Message-ID: <20230314165030.beu2ywtvqa3p45ta@blackpad>
Date:   Tue, 14 Mar 2023 17:50:30 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Waiman Long <longman@...hat.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 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.

Hence,

>  kernel/cgroup/cpuset.c | 3 +++
>  1 file changed, 3 insertions(+)

Reviewed-by: Michal Koutný <mkoutny@...e.com>

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