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Message-ID: <aF1f7aBSzyk7vJty@localhost.localdomain>
Date: Thu, 26 Jun 2025 16:57:49 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Marco Crivellari <marco.crivellari@...e.com>,
Michal Hocko <mhocko@...e.com>,
Peter Zijlstra <peterz@...radead.org>, Tejun Heo <tj@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Vlastimil Babka <vbabka@...e.cz>, Waiman Long <longman@...hat.com>
Subject: Re: [PATCH 00/27] cpuset/isolation: Honour kthreads preferred
affinity
Le Fri, Jun 20, 2025 at 11:08:47AM -0500, Bjorn Helgaas a écrit :
> On Fri, Jun 20, 2025 at 05:22:41PM +0200, Frederic Weisbecker wrote:
> > The kthread code was enhanced lately to provide an infrastructure which
> > manages the preferred affinity of unbound kthreads (node or custom
> > cpumask) against housekeeping constraints and CPU hotplug events.
> >
> > One crucial missing piece is cpuset: when an isolated partition is
> > created, deleted, or its CPUs updated, all the unbound kthreads in the
> > top cpuset are affine to _all_ the non-isolated CPUs, possibly breaking
> > their preferred affinity along the way
> >
> > Solve this with performing the kthreads affinity update from cpuset to
> > the kthreads consolidated relevant code instead so that preferred
> > affinities are honoured.
> >
> > The dispatch of the new cpumasks to workqueues and kthreads is performed
> > by housekeeping, as per the nice Tejun's suggestion.
> >
> > As a welcome side effect, HK_TYPE_DOMAIN then integrates both the set
> > from isolcpus= and cpuset isolated partitions. Housekeeping cpumasks are
> > now modifyable with specific synchronization. A big step toward making
> > nohz_full= also mutable through cpuset in the future.
>
> Is there anything in Documentation/ that covers the "housekeeping"
> feature (and isolation in general) and how to use it? I see a few
> mentions in kernel-parameters.txt and kernel-per-CPU-kthreads.rst, but
> they are only incidental.
Not yet, I'll try that for the next take.
Thanks.
--
Frederic Weisbecker
SUSE Labs
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