linux-kernel - Re: [PATCH 28/33] sched: Switch the fallback task allowed cpumask to HK_TYPE

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Message-ID: <2f892ef9-1965-486d-beab-eacf0b6b0386@redhat.com>
Date: Fri, 26 Dec 2025 18:08:43 -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 28/33] sched: Switch the fallback task allowed cpumask to
 HK_TYPE_DOMAIN

On 12/24/25 8:45 AM, Frederic Weisbecker wrote:
> Tasks that have all their allowed CPUs offline don't want their affinity
> to fallback on either nohz_full CPUs or on domain isolated CPUs. And
> since nohz_full implies domain isolation, checking the latter is enough
> to verify both.
>
> Therefore exclude domain isolation from fallback task affinity.
>
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> ---
>   include/linux/mmu_context.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
> index ac01dc4eb2ce..ed3dd0f3fe19 100644
> --- a/include/linux/mmu_context.h
> +++ b/include/linux/mmu_context.h
> @@ -24,7 +24,7 @@ static inline void leave_mm(void) { }
>   #ifndef task_cpu_possible_mask
>   # define task_cpu_possible_mask(p)	cpu_possible_mask
>   # define task_cpu_possible(cpu, p)	true
> -# define task_cpu_fallback_mask(p)	housekeeping_cpumask(HK_TYPE_TICK)
> +# define task_cpu_fallback_mask(p)	housekeeping_cpumask(HK_TYPE_DOMAIN)
>   #else
>   # define task_cpu_possible(cpu, p)	cpumask_test_cpu((cpu), task_cpu_possible_mask(p))
>   #endif
Acked-by: Waiman Long <longman@...hat.com>