[PATCH 27/33] kthread: Rely on HK_TYPE_DOMAIN for preferred affinity management

[Waiman Long]

On 12/24/25 8:45 AM, Frederic Weisbecker wrote:
> Unbound kthreads want to run neither on nohz_full CPUs nor on domain
> isolated CPUs. And since nohz_full implies domain isolation, checking
> the latter is enough to verify both.
>
> Therefore exclude kthreads from domain isolation.
>
> Signed-off-by: Frederic Weisbecker <frederic at kernel.org>
> ---
>   kernel/kthread.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index 85ccf5bb17c9..968fa5868d21 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -362,18 +362,20 @@ static void kthread_fetch_affinity(struct kthread *kthread, struct cpumask *cpum
>   {
>   	const struct cpumask *pref;
>   
> +	guard(rcu)();
> +
>   	if (kthread->preferred_affinity) {
>   		pref = kthread->preferred_affinity;
>   	} else {
>   		if (kthread->node == NUMA_NO_NODE)
> -			pref = housekeeping_cpumask(HK_TYPE_KTHREAD);
> +			pref = housekeeping_cpumask(HK_TYPE_DOMAIN);
>   		else
>   			pref = cpumask_of_node(kthread->node);
>   	}
>   
> -	cpumask_and(cpumask, pref, housekeeping_cpumask(HK_TYPE_KTHREAD));
> +	cpumask_and(cpumask, pref, housekeeping_cpumask(HK_TYPE_DOMAIN));
>   	if (cpumask_empty(cpumask))
> -		cpumask_copy(cpumask, housekeeping_cpumask(HK_TYPE_KTHREAD));
> +		cpumask_copy(cpumask, housekeeping_cpumask(HK_TYPE_DOMAIN));
>   }
>   
>   static void kthread_affine_node(void)
Reviewed-by: Waiman Long <longman at redhat.com>