Re: [PATCH 2/6] kthread: Keep unbound kthreads off nohz_full CPUs

[Frederic Weisbecker]

Le Tue, Nov 03, 2026 at 08:59:36PM +1300, Matthew Ruffell a écrit :
> From: Caron Wills <caron.wills@xxxxxxxxxx>
> 
> Since commit 041ee6f3727a ("kthread: Rely on HK_TYPE_DOMAIN for
> preferred affinity management") kthread_fetch_affinity() only removes
> domain isolated CPUs from a kthread's affinity, assuming that nohz_full
> CPUs are always domain isolated as well. Up to v6.13 every kthread
> inherited kthreadd's affinity to housekeeping_cpumask(HK_TYPE_KTHREAD),
> and from v6.14 the preferred affinity was filtered with HK_TYPE_KTHREAD,
> so nohz_full CPUs were always excluded.

This was done on purpose because on all setup we have met so far, it didn't
make sense to run nohz_full with load balancing. After all the point is to
run a pinned single task on a single CPU. We have seen too many misconfigured
CPU isolation workloads due to that constraint not being enforced since the
origins.

I'm open to counter-arguments of course but you better have a good case.

Thanks.

-- 
Frederic Weisbecker
SUSE Labs