linux-kernel - Re: [PATCH v10 1/8] timers/migration: Postpone online/offline callbacks registration to late initcall

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Message-ID: <aJSfOf5e4BhAmj2g@localhost.localdomain>
Date: Thu, 7 Aug 2025 14:42:33 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Gabriele Monaco <gmonaco@...hat.com>
Cc: linux-kernel@...r.kernel.org,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Waiman Long <longman@...hat.com>
Subject: Re: [PATCH v10 1/8] timers/migration: Postpone online/offline
 callbacks registration to late initcall

Le Wed, Aug 06, 2025 at 11:38:48AM +0200, Gabriele Monaco a écrit :
> From: Frederic Weisbecker <frederic@...nel.org>
> 
> During the early boot process, the default clocksource used for
> timekeeping is the jiffies. Better clocksources can only be selected
> once clocksource_done_booting() is called as an fs initcall.
> 
> NOHZ can only be enabled after that stage, making global timer migration
> irrelevant up to that point.
> 
> Therefore, don't bother with trashing the cache within that tree from
> the SMP bootup until NOHZ even matters.

I think I made a mistake with this sentence. Actually the timers are not
propagated to the tree before nohz is enabled. So the sentence should
actually be:

"The tree remains inactive before NOHZ is enabled anyway. Therefore it
makes sense to enable each CPUs to the tree only once that is setup."

Thanks.
-- 
Frederic Weisbecker
SUSE Labs