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Message-ID: <20230317180157.uqlleobldg53pgj6@blackpad>
Date: Fri, 17 Mar 2023 19:01:57 +0100
From: Michal Koutný <mkoutny@...e.com>
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,
Will Deacon <will@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>
Subject: Re: [PATCH v2 3/4] cgroup/cpuset: Include offline CPUs when tasks'
cpumasks in top_cpuset are updated
Hello.
On Fri, Mar 17, 2023 at 11:15:07AM -0400, Waiman Long <longman@...hat.com> wrote:
> * Iterate through each task of @cs updating its cpus_allowed to the
> * effective cpuset's. As this function is called with cpuset_rwsem held,
> - * cpuset membership stays stable.
> + * cpuset membership stays stable. For top_cpuset, task_cpu_possible_mask()
> + * is used instead of effective_cpus to make sure all offline CPUs are also
> + * included as hotplug code won't update cpumasks for tasks in top_cpuset.
> */
On Wed, Mar 15, 2023 at 11:06:20AM +0100, Michal Koutný <mkoutny@...e.com> wrote:
> I see now that it returns offlined cpus to top cpuset's tasks.
I considered only the "base" set change cs->effective_cpus ->
possible_mask. (Apologies for that mistake.)
However, I now read the note about subparts_cpus
> * effective_cpus contains only onlined CPUs, but subparts_cpus
> * may have offlined ones.
So if subpart_cpus keeps offlined CPUs, they will be subtracted from
possible_mask and absent in the resulting new_cpus, i.e. undesirable for
the tasks in that cpuset :-/
Michal
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