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

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Message-ID: <alpine.LSU.2.21.2503261547000.4152@pobox.suse.cz>
Date: Wed, 26 Mar 2025 15:52:32 +0100 (CET)
From: Miroslav Benes <mbenes@...e.cz>
To: Peter Zijlstra <peterz@...radead.org>
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, 26 Mar 2025, Peter Zijlstra wrote:

> 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 :-)

Right :)
 
> > 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.

Good.

> 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.

Makes sense.

So I am all for the patch. See my comment elsewhere though.

Miroslav