Re: [PATCH 00/27] cpuset/isolation: Honour kthreads preferred affinity

[Frederic Weisbecker]

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