linux-kernel - Re: [PATCH v5] cpuset: Avoid invalidating sibling partitions on cpuset.cpus conflict.

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Message-ID: <ur4ukfqtqq5jfmuia4tbvsdz3jn3zk6nx2ok4xtnlxth6ulrql@nmetgsxm3lik>
Date: Wed, 26 Nov 2025 15:13:26 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Waiman Long <llong@...hat.com>
Cc: Sun Shaojie <sunshaojie@...inos.cn>, chenridong@...weicloud.com, 
	cgroups@...r.kernel.org, hannes@...xchg.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, shuah@...nel.org, tj@...nel.org
Subject: Re: [PATCH v5] cpuset: Avoid invalidating sibling partitions on
 cpuset.cpus conflict.

On Mon, Nov 24, 2025 at 05:30:47PM -0500, Waiman Long <llong@...hat.com> wrote:
> In the example above, the final configuration is A1:0-1 & B1:1-2. As the cpu
> lists overlap, we can't have both of them as valid partition roots. So
> either one of A1 or B1 is valid or they are both invalid. The current code
> makes them both invalid no matter the operation ordering.  This patch will
> make one of them valid given the operation ordering above. To minimize
> partition invalidation, we will have to live with the fact that it will be
> first-come first-serve as noted by Michal. I am not against this, we just
> have to document it. However, the following operation order will still make
> both of them invalid:

I'm skeptical of the FCFS behavior since I'm afraid it may be subject to
race conditions in practice.
BTW should cpuset.cpus and cpuset.cpus.exclusive have different behavior
in this regard?

Thanks,
Michal

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