linux-kernel - Re: [PATCH 22/33] sched/isolation: Remove HK_TYPE_TICK test from cpu_is

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Message-ID: <bc573163-c5a8-4bb9-a280-45ca48431999@redhat.com>
Date: Fri, 26 Dec 2025 16:26:55 -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 22/33] sched/isolation: Remove HK_TYPE_TICK test from
 cpu_is_isolated()

On 12/24/25 8:45 AM, Frederic Weisbecker wrote:
> It doesn't make sense to use nohz_full without also isolating the
> related CPUs from the domain topology, either through the use of
> isolcpus= or cpuset isolated partitions.
>
> And now HK_TYPE_DOMAIN includes all kinds of domain isolated CPUs.
>
> This means that HK_TYPE_KERNEL_NOISE (of which HK_TYPE_TICK is only an
> alias) should always be a subset of HK_TYPE_DOMAIN.
>
> Therefore if a CPU is not HK_TYPE_DOMAIN, it shouldn't be
> HK_TYPE_KERNEL_NOISE either. Testing the former is then enough.
>
> Simplify cpu_is_isolated() accordingly.
>
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> ---
>   include/linux/sched/isolation.h | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
> index 19905adbb705..cbb1d30f699a 100644
> --- a/include/linux/sched/isolation.h
> +++ b/include/linux/sched/isolation.h
> @@ -82,8 +82,7 @@ static inline bool housekeeping_cpu(int cpu, enum hk_type type)
>   
>   static inline bool cpu_is_isolated(int cpu)
>   {
> -	return !housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN) ||
> -	       !housekeeping_test_cpu(cpu, HK_TYPE_TICK);
> +	return !housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN);
>   }
>   
>   #endif /* _LINUX_SCHED_ISOLATION_H */
Acked-by: Waiman Long <longman@...hat.com>