linux-kernel - Re: [RFC 2/3] kernel/cpu: Mark nonboot cpus as inactive when shutting down nonboot cpus

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Message-ID: <874irhvrb9.ffs@tglx>
Date: Wed, 29 Oct 2025 13:13:46 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Pingfan Liu <piliu@...hat.com>
Cc: kexec@...ts.infradead.org, linux-kernel@...r.kernel.org, Waiman Long
 <longman@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Juri Lelli
 <juri.lelli@...hat.com>, Pierre Gondois <pierre.gondois@....com>, Andrew
 Morton <akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>, Ingo
 Molnar <mingo@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt
 <rostedt@...dmis.org>, Valentin Schneider <vschneid@...hat.com>, "Rafael
 J. Wysocki" <rafael.j.wysocki@...el.com>, Joel Granados
 <joel.granados@...nel.org>
Subject: Re: [RFC 2/3] kernel/cpu: Mark nonboot cpus as inactive when
 shutting down nonboot cpus

On Wed, Oct 29 2025 at 19:36, Pingfan Liu wrote:
> On Tue, Oct 28, 2025 at 01:59:11PM +0100, Thomas Gleixner wrote:
>> If you freeze stuff there is nothing to do. Hibernation works exactly
>> that way without any magic hacks in a particular scheduling class, no?
>> 
>
> There is a nuance: DL bandwidth represents a commitment, not necessarily
> the actual payload. Even a blocked DL task still occupies DL bandwidth.
> The system's DL bandwidth remains unchanged as long as the CPUs stay
> online, which is the case in hibernation.

No. Hibernation brings the non-boot CPUs down in order to create the
disk image.

Thanks,

        tglx