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

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Message-ID: <Z_cjv0EJ45NShYOp@sultan-box.localdomain>
Date: Wed, 9 Apr 2025 18:49:51 -0700
From: Sultan Alsawaf <sultan@...neltoast.com>
To: Xuewen Yan <xuewen.yan94@...il.com>
Cc: Stephan Gerhold <stephan.gerhold@...aro.org>,
	"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, regressions@...ts.linux.dev,
	Johan Hovold <johan@...nel.org>
Subject: Re: [PATCH 1/2] cpufreq: schedutil: Fix superfluous updates caused
 by need_freq_update

On Wed, Apr 09, 2025 at 07:48:05PM +0800, Xuewen Yan wrote:
> Or can we modify it as follows?
> 
> -->8--
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 1a19d69b91ed..0e8d3b92ffe7 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -83,7 +83,7 @@ static bool sugov_should_update_freq(struct
> sugov_policy *sg_policy, u64 time)
> 
>         if (unlikely(sg_policy->limits_changed)) {
>                 sg_policy->limits_changed = false;
> -               sg_policy->need_freq_update =
> cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS);
> +               sg_policy->need_freq_update = true;
>                 return true;
>         }
> 
> @@ -95,11 +95,15 @@ static bool sugov_should_update_freq(struct
> sugov_policy *sg_policy, u64 time)
>  static bool sugov_update_next_freq(struct sugov_policy *sg_policy, u64 time,
>                                    unsigned int next_freq)
>  {
> -       if (sg_policy->need_freq_update)
> +       if (sg_policy->need_freq_update) {
>                 sg_policy->need_freq_update = false;
> -       else if (sg_policy->next_freq == next_freq)
> -               return false;
> +               if (cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS))
> +                       goto change;
> +       }
> 
> +       if (sg_policy->next_freq == next_freq)
> +               return false;
> +change:
>         sg_policy->next_freq = next_freq;
>         sg_policy->last_freq_update_time = time;

If CPUFREQ_NEED_UPDATE_LIMITS isn't specified, then there's no need to request a
frequency switch from the driver when the current frequency is exactly the same
as the next frequency.

Sultan