linux-kernel - Re: [PATCH 19/33] sched/isolation: Remove HK_TYPE_TICK test from cpu_is

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Message-ID: <152b067c-1fa3-4b73-98f3-7e0a0c87e388@redhat.com>
Date: Tue, 2 Sep 2025 11:48:16 -0400
From: Waiman Long <llong@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>,
 LKML <linux-kernel@...r.kernel.org>
Cc: Ingo Molnar <mingo@...hat.com>,
 Marco Crivellari <marco.crivellari@...e.com>, Michal Hocko
 <mhocko@...e.com>, Peter Zijlstra <peterz@...radead.org>,
 Tejun Heo <tj@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 19/33] sched/isolation: Remove HK_TYPE_TICK test from
 cpu_is_isolated()


On 9/2/25 10:28 AM, Waiman Long wrote:
>
> On 8/29/25 11:48 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) is always a superset of HK_TYPE_DOMAIN.
>
> That may not be true. Users can still set "isolcpus=" and "nohz_full=" 
> with disjoint set of CPUs whether cpuset is used for additional 
> isolated CPUs or not.

Instead of "is always a superset", I would prefer to use "should always 
be a superset" as it is a recommendation but users can still violate it.

Cheers,
Longman