linux-kernel - Re: [PATCH] cpufreq: Break out early when frequency equals target

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Date:	Thu, 08 May 2014 18:46:09 +0300
From:	Stratos Karafotis <stratosk@...aphore.gr>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>
CC:	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: Break out early when frequency equals target_freq

On 29/04/2014 11:28 μμ, Stratos Karafotis wrote:
> Many drivers keep frequencies in frequency table in ascending
> or descending order. When governor tries to change to policy->min
> or policy->max respectively then the cpufreq_frequency_table_target
> could return on first iteration. This will save some iteration cycles.
> 
> So, break out early when a frequency in cpufreq_frequency_table
> equals to target one.
> 
> Testing this during kernel compilation using ondemand governor
> with a frequency table in ascending order, the
> cpufreq_frequency_table_target returned early on the first
> iteration at about 30% of times called.
> 
> Signed-off-by: Stratos Karafotis <stratosk@...aphore.gr>
> ---
>  drivers/cpufreq/freq_table.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cpufreq/freq_table.c b/drivers/cpufreq/freq_table.c
> index 8e518c6..1632981 100644
> --- a/drivers/cpufreq/freq_table.c
> +++ b/drivers/cpufreq/freq_table.c
> @@ -137,9 +137,13 @@ int cpufreq_frequency_table_target(struct cpufreq_policy *policy,
>  		i = pos - table;
>  		if ((freq < policy->min) || (freq > policy->max))
>  			continue;
> +		if (freq == target_freq) {
> +			optimal.driver_data = i;
> +			break;
> +		}
>  		switch (relation) {
>  		case CPUFREQ_RELATION_H:
> -			if (freq <= target_freq) {
> +			if (freq < target_freq) {
>  				if (freq >= optimal.frequency) {
>  					optimal.frequency = freq;
>  					optimal.driver_data = i;
> @@ -152,7 +156,7 @@ int cpufreq_frequency_table_target(struct cpufreq_policy *policy,
>  			}
>  			break;
>  		case CPUFREQ_RELATION_L:
> -			if (freq >= target_freq) {
> +			if (freq > target_freq) {
>  				if (freq <= optimal.frequency) {
>  					optimal.frequency = freq;
>  					optimal.driver_data = i;
> 

Gentle reminder.

Thanks,
Stratos
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