linux-kernel - Re: [PATCH V2 3/4] cpufreq: stats: Enable stats for fast-switch as well

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Date:   Wed, 23 Sep 2020 17:14:49 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Lukasz Luba <lukasz.luba@....com>, cristian.marussi@....com,
        Sudeep Holla <sudeep.holla@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 3/4] cpufreq: stats: Enable stats for fast-switch as well

On Wed, Sep 16, 2020 at 8:46 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> Now that all the blockers are gone for enabling stats in fast-switching
> case, enable it.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/cpufreq/cpufreq.c       | 6 +++++-
>  drivers/cpufreq/cpufreq_stats.c | 6 ------
>  2 files changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 47aa90f9a7c2..d5fe64e96be9 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2057,8 +2057,12 @@ unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
>                                         unsigned int target_freq)
>  {
>         target_freq = clamp_val(target_freq, policy->min, policy->max);
> +       target_freq = cpufreq_driver->fast_switch(policy, target_freq);
>
> -       return cpufreq_driver->fast_switch(policy, target_freq);
> +       if (target_freq)
> +               cpufreq_stats_record_transition(policy, target_freq);

So this adds two extra branches in the scheduler path for the cases
when the stats are not used at all which seems avoidable to some
extent.

Can we check policy->stats upfront here and bail out right away if it
is not set, for example?

> +
> +       return target_freq;
>  }
>  EXPORT_SYMBOL_GPL(cpufreq_driver_fast_switch);
>
> diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
> index 314fa1d506d0..daea17f0c36c 100644
> --- a/drivers/cpufreq/cpufreq_stats.c
> +++ b/drivers/cpufreq/cpufreq_stats.c
> @@ -69,9 +69,6 @@ static ssize_t show_time_in_state(struct cpufreq_policy *policy, char *buf)
>         ssize_t len = 0;
>         int i;
>
> -       if (policy->fast_switch_enabled)
> -               return 0;
> -
>         for (i = 0; i < stats->state_num; i++) {
>                 if (pending) {
>                         if (i == stats->last_index)
> @@ -115,9 +112,6 @@ static ssize_t show_trans_table(struct cpufreq_policy *policy, char *buf)
>         ssize_t len = 0;
>         int i, j, count;
>
> -       if (policy->fast_switch_enabled)
> -               return 0;
> -
>         len += scnprintf(buf + len, PAGE_SIZE - len, "   From  :    To\n");
>         len += scnprintf(buf + len, PAGE_SIZE - len, "         : ");
>         for (i = 0; i < stats->state_num; i++) {
> --
> 2.25.0.rc1.19.g042ed3e048af
>