linux-kernel - Re: [PATCH linux-next] cpufreq: governors: Calculate iowait time only when necessary

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Date:	Thu, 28 Feb 2013 12:28:11 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Stratos Karafotis <stratosk@...aphore.gr>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH linux-next] cpufreq: governors: Calculate iowait time only
 when necessary

On Wed, Feb 27, 2013 at 11:14 PM, Stratos Karafotis
<stratosk@...aphore.gr> wrote:
> Currently we always calculate the CPU iowait time and add it to idle time.
> If we are in ondemand and we use io_is_busy, we re-calculate iowait time
> and we subtract it from idle time.
>
> With this patch iowait time is calculated only when necessary avoiding
> the double call to get_cpu_iowait_time_us. We use a parameter in
> function get_cpu_idle_time to distinguish when the iowait time will be
> added to idle time or not, without the need of keeping the prev_io_wait.
>
> Signed-off-by: Stratos Karafotis <stratosk@...aphore.gr>
> ---
>  drivers/cpufreq/cpufreq_conservative.c |  2 +-
>  drivers/cpufreq/cpufreq_governor.c     | 46 +++++++++++++---------------------
>  drivers/cpufreq/cpufreq_governor.h     |  3 +--
>  drivers/cpufreq/cpufreq_ondemand.c     | 11 +++++++-
>  4 files changed, 29 insertions(+), 33 deletions(-)

I have really spent some 10-15 minutes reviewing this patch as initially it
looked to me like something is missing here and calculations are going wrong.

But it was fine :)


> diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
> index f3eb26c..46be2c4 100644
> --- a/drivers/cpufreq/cpufreq_ondemand.c
> +++ b/drivers/cpufreq/cpufreq_ondemand.c
> @@ -339,11 +339,20 @@ static ssize_t store_io_is_busy(struct kobject *a, struct attribute *b,
>  {

> +       /* we need to re-evaluate prev_cpu_idle */
> +       for_each_online_cpu(j) {
> +               struct od_cpu_dbs_info_s *dbs_info;
> +               dbs_info = &per_cpu(od_cpu_dbs_info, j);

Probably squash above two lines and give a blank line after it.

> +               dbs_info->cdbs.prev_cpu_idle = get_cpu_idle_time(j,
> +                       &dbs_info->cdbs.prev_cpu_wall, od_tuners.io_is_busy);
> +       }
>         return count;
>  }

And after that add my:

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
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