linux-kernel - Re: [PATCH v4 8/9] cgroup/cpuset: Documentation update for partition

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Message-ID: <a429e60a-fc4f-60b0-3978-71596fed9542@redhat.com>
Date:   Mon, 10 Jul 2023 20:53:18 -0400
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Juri Lelli <juri.lelli@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Mrunal Patel <mpatel@...hat.com>,
        Ryan Phillips <rphillips@...hat.com>,
        Brent Rowsell <browsell@...hat.com>,
        Peter Hunt <pehunt@...hat.com>, Phil Auld <pauld@...hat.com>
Subject: Re: [PATCH v4 8/9] cgroup/cpuset: Documentation update for partition

On 7/10/23 20:42, Tejun Heo wrote:
> Hello,
>
> On Mon, Jul 10, 2023 at 08:21:43PM -0400, Waiman Long wrote:
>>> Wouldn't a partition root's cpus.exclusive always contain all of the CPUs in
>>> its cpus? Would it make sense for cpus.exclusive to be different from .cpus?
>> In auto-filled case, it should be the same as cpuset.cpus. I will clarify
>> that in the documentation. Thanks for catching that.
> When the user writes something to the file, what would it mena if the
> content differs from the cgroup's cpuset.cpus?

For local partition, it doesn't make sense to have a 
cpust.cpus.exclusive that is not the same as cpuset.cpus as it 
artificially reduce the set of CPUs that can be used in a partition. In 
the case of a remote partition, the ancestor cgroups of a remote 
partition should have cpuset.cpus.exclusive smaller than cpuset.cpus so 
that when the remote partition is enabled, there are still CPUs left to 
be used by those cgroups. In essence, the cpuset.cpus.exclusive 
represents the CPUs that may not be usable anymore if they are taken by 
a remote partition downstream.

Cheers,
Longman