linux-kernel - Re: [PATCH] cpufreq: Change default transition delay to 2ms

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Message-ID: <20240223132736.xp3c3k4k6y2a2ep7@airbuntu>
Date: Fri, 23 Feb 2024 13:27:36 +0000
From: Qais Yousef <qyousef@...alina.io>
To: Pierre Gondois <pierre.gondois@....com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Christian.Loehle@....com
Subject: Re: [PATCH] cpufreq: Change default transition delay to 2ms

On 02/23/24 10:48, Pierre Gondois wrote:

> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 66cef33c4ec7..668263c53810 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -576,8 +576,17 @@ unsigned int cpufreq_policy_transition_delay_us(struct cpufreq_policy *policy)
> >          latency = policy->cpuinfo.transition_latency / NSEC_PER_USEC;
> >          if (latency) {
> > +               unsigned int max_delay_us = 2 * MSEC_PER_SEC;;
> > +
> > +               /*
> > +                * If the platform already has high transition_latency, use it
> > +                * as-is.
> > +                */
> > +               if (latency > max_delay_us)
> > +                       return latency;
> > +
> >                  /*
> > -                * For platforms that can change the frequency very fast (< 10
> > +                * For platforms that can change the frequency very fast (< 20
> 
> I think it should be 10->2us as we do:
>   min(latency * 1000, 2ms)

Yeah I meant 2, that was a typo

Thanks

-->8--

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 66cef33c4ec7..de92a9912587 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -576,8 +576,17 @@ unsigned int cpufreq_policy_transition_delay_us(struct cpufreq_policy *policy)

        latency = policy->cpuinfo.transition_latency / NSEC_PER_USEC;
        if (latency) {
+               unsigned int max_delay_us = 2 * MSEC_PER_SEC;;
+
+               /*
+                * If the platform already has high transition_latency, use it
+                * as-is.
+                */
+               if (latency > max_delay_us)
+                       return latency;
+
                /*
-                * For platforms that can change the frequency very fast (< 10
+                * For platforms that can change the frequency very fast (< 2
                 * us), the above formula gives a decent transition delay. But
                 * for platforms where transition_latency is in milliseconds, it
                 * ends up giving unrealistic values.
@@ -586,7 +595,7 @@ unsigned int cpufreq_policy_transition_delay_us(struct cpufreq_policy *policy)
                 * a reasonable amount of time after which we should reevaluate
                 * the frequency.
                 */
-               return min(latency * LATENCY_MULTIPLIER, (unsigned int)(2 * MSEC_PER_SEC));
+               return min(latency * LATENCY_MULTIPLIER, max_delay_us);
        }

        return LATENCY_MULTIPLIER;