From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michal =?utf-8?Q?Koutn=C3=BD?= <mkoutny-IBi9RG/b67k@public.gmane.org>
Subject: Re: [PATCH v2 3/4] cgroup/cpuset: Include offline CPUs when tasks'
 cpumasks in top_cpuset are updated
Date: Fri, 17 Mar 2023 19:01:57 +0100
Message-ID: <20230317180157.uqlleobldg53pgj6@blackpad>
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To: Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Zefan Li <lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Shuah Khan <shuah-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kselftest-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Will Deacon <will-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Juri Lelli <juri.lelli-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>


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Hello.

On Fri, Mar 17, 2023 at 11:15:07AM -0400, Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> =
wrote:
>   * Iterate through each task of @cs updating its cpus_allowed to the
>   * effective cpuset's.  As this function is called with cpuset_rwsem hel=
d,
> - * cpuset membership stays stable.
> + * cpuset membership stays stable. For top_cpuset, task_cpu_possible_mas=
k()
> + * is used instead of effective_cpus to make sure all offline CPUs are a=
lso
> + * included as hotplug code won't update cpumasks for tasks in top_cpuse=
t.
>   */

On Wed, Mar 15, 2023 at 11:06:20AM +0100, Michal Koutn=FD <mkoutny-IBi9RG/b67k@public.gmane.org=
> wrote:
> I see now that it returns offlined cpus to top cpuset's tasks.

I considered only the "base" set change cs->effective_cpus ->
possible_mask. (Apologies for that mistake.)

However, I now read the note about subparts_cpus

>         * effective_cpus contains only onlined CPUs, but subparts_cpus
>         * may have offlined ones.

So if subpart_cpus keeps offlined CPUs, they will be subtracted from
possible_mask and absent in the resulting new_cpus, i.e. undesirable for
the tasks in that cpuset :-/

Michal

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