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

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Message-ID: <aNFpNijJ0tT0rjPa@2a01cb069018a81087c6c9b3bf9471d3.ipv6.abo.wanadoo.fr>
Date: Mon, 22 Sep 2025 17:20:22 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Waiman Long <llong@...hat.com>
Cc: LKML <linux-kernel@...r.kernel.org>, 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()

Le Tue, Sep 02, 2025 at 11:48:16AM -0400, Waiman Long a écrit :
> 
> 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.

Good point!

> Cheers,
> Longman
> 

-- 
Frederic Weisbecker
SUSE Labs