linux-kernel - Re: [RFC PATCH 0/5] cgroup/cpuset: A new "isolcpus" paritition

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Date:   Tue, 6 Jun 2023 10:13:31 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Michal Koutný <mkoutny@...e.com>,
        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: [RFC PATCH 0/5] cgroup/cpuset: A new "isolcpus" paritition

Hello,

On Tue, Jun 06, 2023 at 04:11:02PM -0400, Waiman Long wrote:
...
> The current CPU exclusive behavior is limited to sibling cgroups only.
> Because of the hierarchical nature of cpu distribution, the set of exclusive
> CPUs have to appear in all its ancestors. When partition is enabled, we do a
> sibling exclusivity test at that point to verify that it is exclusive. It
> looks like you want to do an exclusivity test even when the partition isn't
> active. I can certainly do that when the file is being updated. However, it
> will fail the write if the exclusivity test fails just like the v1
> cpuset.cpus.exclusive flag if you are OK with that.

Yeah, doesn't look like there's a way around it if we want to make
.exclusive a feature which is useful on its own.

> > Instead, it can be sth like "if the parent is a
> > partition root, cpuset implicitly tries to set all CPUs in its cpus file in
> > its cpus.exclusive file" so that user-visible behavior stays unchanged
> > depending on past history.
> 
> If parent is a partition root, auto reservation will be done and
> cpus.exclusive will be set automatically just like before. So existing
> applications using partition will not be affected.

Sounds great.

Thanks.

-- 
tejun