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

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Date:   Tue, 10 Nov 2020 13:53:08 +0100
From:   Thomas Renninger <trenn@...e.de>
To:     Rafael Wysocki <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     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

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):
 
> /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:

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...

   Thomas