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

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Message-ID: <46a613e8-cf5b-4fbc-9299-48ab1a6f347b@redhat.com>
Date: Fri, 26 Dec 2025 17:16:54 -0500
From: Waiman Long <llong@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>,
 LKML <linux-kernel@...r.kernel.org>
Cc: Michal Koutný <mkoutny@...e.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Catalin Marinas <catalin.marinas@....com>,
 Chen Ridong <chenridong@...wei.com>, Danilo Krummrich <dakr@...nel.org>,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Gabriele Monaco <gmonaco@...hat.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Ingo Molnar <mingo@...hat.com>, Jakub Kicinski <kuba@...nel.org>,
 Jens Axboe <axboe@...nel.dk>, Johannes Weiner <hannes@...xchg.org>,
 Lai Jiangshan <jiangshanlai@...il.com>,
 Marco Crivellari <marco.crivellari@...e.com>, Michal Hocko
 <mhocko@...e.com>, Muchun Song <muchun.song@...ux.dev>,
 Paolo Abeni <pabeni@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Phil Auld <pauld@...hat.com>, "Rafael J . Wysocki" <rafael@...nel.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Shakeel Butt <shakeel.butt@...ux.dev>, Simon Horman <horms@...nel.org>,
 Tejun Heo <tj@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>,
 cgroups@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-block@...r.kernel.org, linux-mm@...ck.org, linux-pci@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH 27/33] kthread: Rely on HK_TYPE_DOMAIN for preferred
 affinity management

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@...nel.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@...hat.com>