linux-kernel - Re: [PATCH] cgroup/cpuset: Disable cpuset_cpumask_can

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Message-ID: <ZzZFKpuX-edQ1GuO@slm.duckdns.org>
Date: Thu, 14 Nov 2024 08:44:58 -1000
From: Tejun Heo <tj@...nel.org>
To: Waiman Long <longman@...hat.com>
Cc: Johannes Weiner <hannes@...xchg.org>,
	Michal Koutný <mkoutny@...e.com>,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Juri Lelli <juri.lelli@...hat.com>, Phil Auld <pauld@...hat.com>
Subject: Re: [PATCH] cgroup/cpuset: Disable cpuset_cpumask_can_shrink() test
 if not load balancing

On Thu, Nov 14, 2024 at 01:19:15PM -0500, Waiman Long wrote:
> With some recent proposed changes [1] in the deadline server code,
> it has caused a test failure in test_cpuset_prs.sh when a change
> is being made to an isolated partition. This is due to failing
> the cpuset_cpumask_can_shrink() check for SCHED_DEADLINE tasks at
> validate_change().
> 
> This is actually a false positive as the failed test case involves an
> isolated partition with load balancing disabled. The deadline check
> is not meaningful in this case and the users should know what they
> are doing.
> 
> Fix this by doing the cpuset_cpumask_can_shrink() check only when loading
> balanced is enabled. Also change its arguments to use effective_cpus
> for the current cpuset and user_xcpus() as an approiximation for the
> target effective_cpus as the real effective_cpus hasn't been fully
> computed yet as this early stage.
> 
> As the check isn't comprehensive, there may be false positives or
> negatives. We may have to revise the code to do a more thorough check
> in the future if this becomes a concern.
> 
> [1] https://lore.kernel.org/lkml/82be06c1-6d6d-4651-86c9-bcc828cbcb80@redhat.com/T/#t
> 
> Signed-off-by: Waiman Long <longman@...hat.com>

Applied to cgroup/for-6.13.

Thanks.

-- 
tejun