linux-kernel - Re: [PATCH] cpufreq: Avoid unnecessary frequency updates due to mismatch

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Date:   Thu, 5 May 2022 15:31:54 +0200
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rex-BC Chen <rex-bc.chen@...iatek.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH] cpufreq: Avoid unnecessary frequency updates due to
 mismatch



On 04/05/2022 10:21, Viresh Kumar wrote:
> For some platforms, the frequency returned by hardware may be slightly
> different from what is provided in the frequency table. For example,
> hardware may return 499 MHz instead of 500 MHz. In such cases it is
> better to avoid getting into unnecessary frequency updates, as we may
> end up switching policy->cur between the two and sending unnecessary
> pre/post update notifications, etc.
> 
> This patch has chosen allows the hardware frequency and table frequency
> to deviate by 1 MHz for now, we may want to increase it a bit later on
> if someone still complains.
> 
> Reported-by: Rex-BC Chen <rex-bc.chen@...iatek.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>

Reviewed-by: Matthias Brugger <matthias.bgg@...il.com>

> ---
>   drivers/cpufreq/cpufreq.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 0d58b0f8f3af..233e8af48848 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -28,6 +28,7 @@
>   #include <linux/suspend.h>
>   #include <linux/syscore_ops.h>
>   #include <linux/tick.h>
> +#include <linux/units.h>
>   #include <trace/events/power.h>
>   
>   static LIST_HEAD(cpufreq_policy_list);
> @@ -1708,6 +1709,16 @@ static unsigned int cpufreq_verify_current_freq(struct cpufreq_policy *policy, b
>   		return new_freq;
>   
>   	if (policy->cur != new_freq) {
> +		/*
> +		 * For some platforms, the frequency returned by hardware may be
> +		 * slightly different from what is provided in the frequency
> +		 * table, for example hardware may return 499 MHz instead of 500
> +		 * MHz. In such cases it is better to avoid getting into
> +		 * unnecessary frequency updates.
> +		 */
> +		if (abs(policy->cur - new_freq) < HZ_PER_MHZ)
> +			return policy->cur;
> +
>   		cpufreq_out_of_sync(policy, new_freq);
>   		if (update)
>   			schedule_work(&policy->update);