linux-kernel - Re: [RFC PATCH 00/86] Make the kernel preemptible

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Message-ID: <20231108111415.GP8262@noisy.programming.kicks-ass.net>
Date:   Wed, 8 Nov 2023 12:14:15 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ankur Arora <ankur.a.arora@...cle.com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
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Subject: Re: [RFC PATCH 00/86] Make the kernel preemptible

On Wed, Nov 08, 2023 at 03:00:44AM -0800, Ankur Arora wrote:

> Ah now I see what you are saying.
> 
> Quick thought: even if we were running under NONE, eventually you'll

Well, NONE, you get what you pay for etc..

> want to forcibly preempt out a CPU hog. So we will need to have
> at least this one enabled always:
> 
> >  *   irqentry_exit_cond_resched <- irqentry_exit_cond_resched
> 
> These two, it might make sense to toggle them based on model.
> 
> >  *   preempt_schedule           <- preempt_schedule
> >  *   preempt_schedule_notrace   <- preempt_schedule_notrace
> 
> Anyway let me think about this more and respond tomorrow.

That's more or less killing NONE. At that point there's really no point
in having it.

I would really suggest you start with transforming VOLUNTARY into the
LAZY thing, keep it as simple and narrow as possible.

Once you've got that done, then you can try and argue that NONE makes no
sense and try and take it out.

Smaller step etc..