linux-kernel - Re: [PATCH 0/5] cgroup/cpuset: Miscellaneous updates

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Message-ID: <20230315162436.GA19015@willie-the-truck>
Date:   Wed, 15 Mar 2023 16:24:36 +0000
From:   Will Deacon <will@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shuah Khan <shuah@...nel.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 0/5] cgroup/cpuset: Miscellaneous updates

Hi Waiman,

On Mon, Mar 06, 2023 at 03:08:44PM -0500, Waiman Long wrote:
> This patch series includes miscellaneous update to the cpuset and its
> testing code.
> 
> Patch 2 is actually a follow-up of commit 3fb906e7fabb ("cgroup/cpuset:
> Don't filter offline CPUs in cpuset_cpus_allowed() for top cpuset tasks").
> 
> Patches 3-4 are for handling corner cases when dealing with
> task_cpu_possible_mask().

Thanks for cc'ing me on these. I ran my arm64 asymmetric tests and, fwiw,
I get the same results as vanilla -rc2, so that's good.

One behaviour that persists (and which I thought might be addressed by this
series) is the following. Imagine a 4-CPU system with CPUs 0-1 being 64-bit
only. If I configure a parent cpuset with 'cpuset.cpus' of "0-2" and a
child cpuset with 'cpuset.cpus' of "0-1", then attaching a 32-bit task
to the child cpuset will result in an affinity mask of 4. If I then change
'cpuset.cpus' of the parent cpuset to "0-1,3", the affinity mask of the
task remains at '4' whereas it might be nice to update it to '8', in-line
with the new affinity mask of the parent cpuset.

Anyway, I'm not complaining (this is certainly _not_ a regression), but
I thought I'd highlight it in case you were aiming to address this with
your changes.

Cheers,

Will