From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj@kernel.org>
Subject: Re: [RFC PATCH 0/5] cgroup/cpuset: A new "isolcpus" paritition
Date: Tue, 6 Jun 2023 10:13:31 -1000
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Sender: Tejun Heo <htejun@gmail.com>
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To: Waiman Long <longman@redhat.com>
Cc: Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>, Zefan Li <lizefan.x@bytedance.com>, Johannes Weiner <hannes@cmpxchg.org>, Jonathan Corbet <corbet@lwn.net>, Shuah Khan <shuah@kernel.org>, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Juri Lelli <juri.lelli@redhat.com>, Valentin Schneider <vschneid@redhat.com>, Frederic Weisbecker <frederic@kernel.org>, Mrunal Patel <mpatel@redhat.com>, Ryan Phillips <rphillips@redhat.com>, Brent Rowsell <browsell@redhat.com>, Peter Hunt <pehunt@redhat.com>, Phil Auld <pauld@redhat.com>

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