linux-kernel - Re: [PATCH RESEND 1/2] tick/nohz: Fix wrong NOHZ idle CPU state

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Message-ID: <6f14ff5c-cddb-f450-b4bb-fcc995b5ce5b@gentwo.org>
Date: Thu, 4 Sep 2025 09:10:29 -0700 (PDT)
From: "Christoph Lameter (Ampere)" <cl@...two.org>
To: Frederic Weisbecker <frederic@...nel.org>
cc: Adam Li <adamli@...amperecomputing.com>, anna-maria@...utronix.de, 
    tglx@...utronix.de, mingo@...hat.com, peterz@...radead.org, 
    juri.lelli@...hat.com, vincent.guittot@...aro.org, vschneid@...hat.com, 
    dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, 
    mgorman@...e.de, linux-kernel@...r.kernel.org, patches@...erecomputing.com
Subject: Re: [PATCH RESEND 1/2] tick/nohz: Fix wrong NOHZ idle CPU state

On Thu, 4 Sep 2025, Frederic Weisbecker wrote:

> The current state is indeed broken and some people have already tried to fix it.
> The thing is nohz_full don't want dynamic isolation because it is deemed to run a
> single task. Therefore those tasks must be placed manually in order not to break
> isolation guarantees by accident.
>
> In fact nohz_full doesn't make much sense without isolcpus (or isolated cpuset
> v2 partitions) and I even intend to make nohz_full depend on domain isolation
> in the long term.

I have never used isolcpus with nohz_full. AFAICT isolcpus is depreciated
and cpusets are unnecessary complex overhead.