linux-kernel - Re: [PATCH] cpufreq: stats: Switch to ktime and msec instead of jiffies and usertime

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Date:   Wed, 11 Nov 2020 10:43:50 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Thomas Renninger <trenn@...e.de>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Jonathan Corbet <corbet@....net>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: stats: Switch to ktime and msec instead of
 jiffies and usertime

On 10-11-20, 13:53, Thomas Renninger wrote:
> Am Dienstag, 10. November 2020, 12:07:37 CET schrieb Viresh Kumar:
> > The cpufreq and thermal core, both provide sysfs statistics to help
> > userspace learn about the behavior of frequencies and cooling states.
> > 
> > This is how they look:
> > /sys/devices/system/cpu/cpufreq/policy0/stats/time_in_state:1200000 399
>  
> > The results look like this after this commit:
> > /sys/devices/system/cpu/cpufreq/policy0/stats/time_in_state:1200000 3830
> 
> How would userspace know whether it's ms or 10ms?
> 
> whatabout a new file with the same convention as cooling devices (adding ms):

Keeping two files for same stuff is not great, and renaming the file
breaks userspace ABI. I am not sure what's the right thing to do here.

> > /sys/class/thermal/cooling_device0/stats/time_in_state_ms:state0 3888
> > /sys/devices/system/cpu/cpufreq/policy0/stats/time_in_state_ms:1200000 3830
> 
> Somewhat off-topic, some ideas:
> 
> I wonder how useful these stats still are.
> CPU_FREQ_STAT is off on my system:

I still use it.

> config CPU_FREQ_STAT
>         bool "CPU frequency transition statistics"
>         help
>           Export CPU frequency statistics information through sysfs.
> 
>           If in doubt, say N.
> 
> Iirc this was a module at former times?
> 
> commit 1aefc75b2449eb68a6fc3ca932e2a4ee353b748d
> Author: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Date:   Tue May 31 22:14:44 2016 +0200
> 
>     cpufreq: stats: Make the stats code non-modular
> 
> outlined 2 problems with cpufreq_stats being non-modular, but
> also seem to fix them up:
> ... and drop the notifiers from it
> Make the stats sysfs attributes appear empty if fast frequency
> switching is enabled...

I already fixed this recently and stats don't appear empty for fast
switch anymore.

-- 
viresh