linux-kernel - Re: [RFC PATCH] preempt: Add a generic function to return the preemption string.

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Message-ID: <20250109145408.GB5388@noisy.programming.kicks-ass.net>
Date: Thu, 9 Jan 2025 15:54:08 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	linux-rt-devel@...ts.linux.dev, Ben Segall <bsegall@...gle.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
	Mel Gorman <mgorman@...e.de>, Thomas Gleixner <tglx@...utronix.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Will Deacon <will@...nel.org>, x86@...nel.org
Subject: Re: [RFC PATCH] preempt: Add a generic function to return the
 preemption string.

On Thu, Jan 09, 2025 at 03:41:24PM +0100, Sebastian Andrzej Siewior wrote:
> On 2025-01-09 15:37:01 [+0100], Peter Zijlstra wrote:
> > Upgrade brain. Also the proposed thing was just plain wrong.
> 
> Was it?

Yes, things like:

> +             if (preempt_model_voluntary())
> +                     return "VOLUNTARY+LAZY";
> +             if (preempt_model_none())
> +                     return "NONE+LAZY";

don't exist and make no sense.

> For the !DYNAMIC case everything should be optimized away except
> for the current case.
> Let me try your thing to see what is different…

For the various cases it was supposed to print something like so:

RT+DYN:	 PREEMPT_{RT,(dyn_mode)}
RT+LAZY: PREEMPT_{RT,LAZY}
RT+FULL: PREEMPT_RT

DYN:       PREEMPT_(dyn_mode)
FULL:      PREEMPT
LAZY:      PREEMPT_LAZY
VOLUNTARY: VOLUNTARY
NONE:      NONE