linux-kernel - Re: [PATCH v3 2/2] tracing/preemptirq: Optimize preempt

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Message-ID: <ppdduzdqnd3kwourcmocfi35i7wcbuagmzqgtgmyr55aps774t@37wucnoii7o3>
Date: Tue, 8 Jul 2025 10:09:45 -0300
From: Wander Lairson Costa <wander@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>, 
	Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, 
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Valentin Schneider <vschneid@...hat.com>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, David Woodhouse <dwmw@...zon.co.uk>, 
	Thomas Gleixner <tglx@...utronix.de>, Boqun Feng <boqun.feng@...il.com>, 
	open list <linux-kernel@...r.kernel.org>, "open list:TRACING" <linux-trace-kernel@...r.kernel.org>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Clark Williams <williams@...hat.com>, 
	Gabriele Monaco <gmonaco@...hat.com>
Subject: Re: [PATCH v3 2/2] tracing/preemptirq: Optimize
 preempt_disable/enable() tracepoint overhead

On Mon, Jul 07, 2025 at 01:26:22PM +0200, Peter Zijlstra wrote:
> On Fri, Jul 04, 2025 at 02:07:43PM -0300, Wander Lairson Costa wrote:
> > +#if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_TRACE_PREEMPT_TOGGLE)
> > +#define preempt_count_dec_and_test() \
> > +	({ preempt_count_sub(1); should_resched(0); })
> > +#endif
> 
> Also this is terrible. Surely you can do better.
> 

Thank you for pointing this out. I'm not sure I've fully understood the
concern here. My understanding was that this logic was pre-existing and
my patch only reorganized it.

I'm clearly missing something. Could you please elaborate a bit on the
issue you've spotted?