From: Peter Zijlstra <peterz@infradead.org>
To: Wander Lairson Costa <wander@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Valentin Schneider <vschneid@redhat.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
David Woodhouse <dwmw@amazon.co.uk>,
Thomas Gleixner <tglx@linutronix.de>,
Boqun Feng <boqun.feng@gmail.com>,
open list <linux-kernel@vger.kernel.org>,
"open list:TRACING" <linux-trace-kernel@vger.kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Clark Williams <williams@redhat.com>,
Gabriele Monaco <gmonaco@redhat.com>
Subject: Re: [PATCH v3 2/2] tracing/preemptirq: Optimize preempt_disable/enable() tracepoint overhead
Date: Tue, 8 Jul 2025 20:46:56 +0200 [thread overview]
Message-ID: <20250708184656.GB477119@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <ppdduzdqnd3kwourcmocfi35i7wcbuagmzqgtgmyr55aps774t@37wucnoii7o3>
On Tue, Jul 08, 2025 at 10:09:45AM -0300, Wander Lairson Costa wrote:
> 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?
The normal (!DEBUG) case uses __preempt_count_dec_and_test(), which is
significantly better.
next prev parent reply other threads:[~2025-07-08 18:47 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-04 17:07 [PATCH v3 0/2] tracing/preemptirq: Optimize disabled " Wander Lairson Costa
2025-07-04 17:07 ` [PATCH v3 1/2] trace/preemptirq: reduce overhead of irq_enable/disable tracepoints Wander Lairson Costa
2025-07-06 4:29 ` kernel test robot
2025-07-04 17:07 ` [PATCH v3 2/2] tracing/preemptirq: Optimize preempt_disable/enable() tracepoint overhead Wander Lairson Costa
2025-07-07 10:29 ` kernel test robot
2025-07-07 11:20 ` Peter Zijlstra
2025-07-08 12:54 ` Wander Lairson Costa
2025-07-08 18:54 ` Peter Zijlstra
2025-08-01 13:30 ` Wander Lairson Costa
2025-08-25 11:56 ` Wander Lairson Costa
2025-07-07 11:26 ` Peter Zijlstra
2025-07-08 13:09 ` Wander Lairson Costa
2025-07-08 18:46 ` Peter Zijlstra [this message]
2025-08-01 13:05 ` Wander Lairson Costa
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