linux-kernel - Re: [RFC][PATCH] sched,livepatch: Untangle cond

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Message-ID: <20250326144212.GG25239@noisy.programming.kicks-ass.net>
Date: Wed, 26 Mar 2025 15:42:12 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Miroslav Benes <mbenes@...e.cz>
Cc: Petr Mladek <pmladek@...e.com>, Josh Poimboeuf <jpoimboe@...hat.com>,
	mingo@...nel.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, vschneid@...hat.com, jpoimboe@...nel.org,
	jikos@...nel.org, joe.lawrence@...hat.com,
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [RFC][PATCH] sched,livepatch: Untangle cond_resched() and
 live-patching

On Wed, Mar 26, 2025 at 03:37:50PM +0100, Miroslav Benes wrote:

> If I remember correctly, we had something like this in the old kGraft 
> implementation of the live patching (SUSE way). We exactly had a hook 
> somewhere in the kthread freezing code. This looks much cleaner and as far 
> as I know the fridge went through improvements recently.

Yeah, I rewrote it a while ago :-)

> Peter, so that I understand it correctly... we would rely on all kthreads 
> becoming freezable eventually so that both suspend and livepatch benefit. 
> Is that what you meant by the above?

Well, IIRC (its been a while already) all kthreads should have a
FREEZABLE already. Things like suspend-to-idle don't hit the hotplug
path at all anymore and everything must freeze, otherwise they fail.

I was more meaning the time-to-freeze; if some kthreads take a long time
to freeze/patch then this would want improving on both ends.