linux-kernel - Re: [PATCH] cpufreq: ondemand: Change the calculation of target frequency

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Date:	Fri, 31 May 2013 14:24:59 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Stratos Karafotis <stratosk@...aphore.gr>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH] cpufreq: ondemand: Change the calculation of target frequency

On 31 May 2013 02:37, Stratos Karafotis <stratosk@...aphore.gr> wrote:

Ahh.. earlier mail got sent without me doing complete review :(

> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> +static void od_check_cpu(int cpu, unsigned int load)
>  {
>         struct od_cpu_dbs_info_s *dbs_info = &per_cpu(od_cpu_dbs_info, cpu);
>         struct cpufreq_policy *policy = dbs_info->cdbs.cur_policy;
> @@ -176,29 +170,17 @@ static void od_check_cpu(int cpu, unsigned int load_freq)
>         dbs_info->freq_lo = 0;
>
>         /* Check for frequency increase */
> -       if (load_freq > od_tuners->up_threshold * policy->cur) {
> +       if (load > od_tuners->up_threshold) {

Chances of this getting hit are minimal now.. I don't know if keeping
this will change anything now :)

>                 /* If switching to max speed, apply sampling_down_factor */
>                 if (policy->cur < policy->max)
>                         dbs_info->rate_mult =
>                                 od_tuners->sampling_down_factor;
>                 dbs_freq_increase(policy, policy->max);
>                 return;
> -       }
> -
> -       /* Check for frequency decrease */
> -       /* if we cannot reduce the frequency anymore, break out early */
> -       if (policy->cur == policy->min)
> -               return;
> -
> -       /*
> -        * The optimal frequency is the frequency that is the lowest that can
> -        * support the current CPU usage without triggering the up policy. To be
> -        * safe, we focus 10 points under the threshold.
> -        */
> -       if (load_freq < od_tuners->adj_up_threshold
> -                       * policy->cur) {
> +       } else {
> +               /* Calculate the next frequency proportional to load */
>                 unsigned int freq_next;
> -               freq_next = load_freq / od_tuners->adj_up_threshold;
> +               freq_next = load * policy->max / 100;

Rafael asked why you believe this is the right formula and I really couldn't
find an appropriate answer to that, sorry :(
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