linux-kernel - Re: [PATCH 1/2] cpufreq: schedutil: Fix superfluous updates caused by need_freq

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Message-ID: <CAJZ5v0j3X8BC57bxktxSZN+0XqZSGmdtGZoL8QV-_Um9pSynaA@mail.gmail.com>
Date: Wed, 18 Dec 2024 16:10:03 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Christian Loehle <christian.loehle@....com>, Sultan Alsawaf <sultan@...neltoast.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Viresh Kumar <viresh.kumar@...aro.org>, 
	Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	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>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] cpufreq: schedutil: Fix superfluous updates caused by need_freq_update

On Thu, Dec 12, 2024 at 2:24 PM Christian Loehle
<christian.loehle@....com> wrote:
>
> On 12/12/24 01:57, Sultan Alsawaf wrote:
> > From: "Sultan Alsawaf (unemployed)" <sultan@...neltoast.com>
> >
> > A redundant frequency update is only truly needed when there is a policy
> > limits change with a driver that specifies CPUFREQ_NEED_UPDATE_LIMITS.
> >
> > In spite of that, drivers specifying CPUFREQ_NEED_UPDATE_LIMITS receive a
> > frequency update _all the time_, not just for a policy limits change,
> > because need_freq_update is never cleared.
> >
> > Furthermore, ignore_dl_rate_limit()'s usage of need_freq_update also leads
> > to a redundant frequency update, regardless of whether or not the driver
> > specifies CPUFREQ_NEED_UPDATE_LIMITS, when the next chosen frequency is the
> > same as the current one.
> >
> > Fix the superfluous updates by only honoring CPUFREQ_NEED_UPDATE_LIMITS
> > when there's a policy limits change, and clearing need_freq_update when a
> > requisite redundant update occurs.
> >
> > This is neatly achieved by moving up the CPUFREQ_NEED_UPDATE_LIMITS test
> > and instead setting need_freq_update to false in sugov_update_next_freq().
> >
>
> Good catch!
> Fixes:
> 600f5badb78c ("cpufreq: schedutil: Don't skip freq update when limits change")
>
>
> > Signed-off-by: Sultan Alsawaf (unemployed) <sultan@...neltoast.com>
>
> Reviewed-by: Christian Loehle <christian.loehle@....com>

Applied with the above Fixes tag added as 6.14 material, thanks!