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Message-ID: <xhsmhk09f7dgy.mognet@vschneid.remote.csb>
Date: Fri, 17 Jun 2022 12:10:05 +0100
From: Valentin Schneider <vschneid@...hat.com>
To: Brian Norris <briannorris@...omium.org>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>
Cc: Ben Segall <bsegall@...gle.com>, linux-kernel@...r.kernel.org,
Dietmar Eggemann <dietmar.eggemann@....com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Mel Gorman <mgorman@...e.de>,
Steven Rostedt <rostedt@...dmis.org>,
Brian Norris <briannorris@...omium.org>
Subject: Re: [PATCH] sched: Drop outdated compile-optimization comment
On 15/06/22 15:27, Brian Norris wrote:
> Looks like this exists from way back in 2011 (commit 095c0aa83e52
> ("sched: adjust scheduler cpu power for stolen time")), when there was a
> little more aggressive use of #if around these variables. That #if is
> gone, and the comment just confuses the reader now. (For one, we don't
> call sched_rt_avg_update() directly any more either.)
>
So that sched_rt_avg_update() became update_irq_load_avg() with
91c27493e78d ("sched/irq: Add IRQ utilization tracking")
and then the #ifdef configs were reorganized in
11d4afd4ff66 ("sched/pelt: Fix warning and clean up IRQ PELT config")
I'd argue that comment is still somewhat relevant but it applies to that
block:
#ifdef CONFIG_HAVE_SCHED_AVG_IRQ
if ((irq_delta + steal) && sched_feat(NONTASK_CAPACITY))
update_irq_load_avg(rq, irq_delta + steal);
#endif
if !CONFIG_HAVE_SCHED_AVG_IRQ then yes you'd expect the compiler to not
even add a call to update_irq_load_avg() in there, but compilers aren't the
most trustworthy things :-) If you feel like it, you could play with
GCC/clang and see what they emit if you remove those #ifdefs.
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