Message-ID: <176a4cfd-2902-16a2-b9e7-cb66e1c5b49c@redhat.com>
Date:   Tue, 14 Mar 2023 14:20:53 -0400
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Subject: Re: [PATCH 1/5] cgroup/cpuset: Skip task update if hotplug doesn't
 affect current cpuset
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To:     =?UTF-8?Q?Michal_Koutn=c3=bd?= <mkoutny@suse.com>
Cc:     Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shuah Khan <shuah@kernel.org>, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
References: <20230306200849.376804-1-longman@redhat.com>
 <20230306200849.376804-2-longman@redhat.com>
 <20230314165030.beu2ywtvqa3p45ta@blackpad>
From:   Waiman Long <longman@redhat.com>
In-Reply-To: <20230314165030.beu2ywtvqa3p45ta@blackpad>
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On 3/14/23 12:50, Michal Koutný wrote:
> On Mon, Mar 06, 2023 at 03:08:45PM -0500, Waiman Long <longman@redhat.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