linux-kernel - Re: [PATCH v11 7/8] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst

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Date:   Tue, 28 Jun 2022 04:10:29 +0900
From:   Tejun Heo <tj@...nel.org>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Waiman Long <longman@...hat.com>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <shuah@...nel.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Phil Auld <pauld@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH v11 7/8] cgroup/cpuset: Update description of
 cpuset.cpus.partition in cgroup-v2.rst

Hello,

On Tue, Jun 14, 2022 at 01:53:45PM +0200, Michal Koutný wrote:
> On Mon, Jun 13, 2022 at 08:00:56AM -1000, Tejun Heo <tj@...nel.org> wrote:
> > Yeah, I don't know why this part is different from any other errors that the
> > parent can make.
> 
> It's different because a write to parent's cpuset.cpus is independent of
> whether cpuset.cpus of its children are exclusive or not.
> In an extreme case the children may be non-exclusive
> 
>     parent	cpuset.cpus=0-3 //   valid partition
>     `- child_1	cpuset.cpus=0-1	// invalid partition
>     `- child_2	cpuset.cpus=1-2 // invalid partition
> 
> but the parent can still be a valid partition (thanks to cpu no. 3 in
> the example above).
> 
> Do I miss anything?

What I'm trying to say is that cpuset.cpus of child_1 and child_2 are
owned by the parent, so a feature which blocks siblings from
intersecting each other doesn't make whole lot of sense because all
those files are under the control of the parent who would have the
power to enable or disable the restrition anyway.

The partition mode file is owned by the parent too, right? So, all
these are to be configured by the same entity and the errors can be
reported the same way, no?

Thanks.

-- 
tejun