linux-kernel - Re: [PATCH] intel_pstate: track and export frequency residency stats via sysfs.

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Date:	Thu, 11 Sep 2014 08:37:26 -0700
From:	Dirk Brandewie <dirk.brandewie@...il.com>
To:	Sameer Nanda <snanda@...omium.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	dirk.brandewie@...il.com,
	Anup Chenthamarakshan <anupc@...omium.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] intel_pstate: track and export frequency residency stats
 via sysfs.

On 09/10/2014 06:04 PM, Sameer Nanda wrote:
> On Wed, Sep 10, 2014 at 5:04 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>> On Wednesday, September 10, 2014 04:39:05 PM Anup Chenthamarakshan wrote:
>>> On Thu, Sep 11, 2014 at 12:49:48AM +0200, Rafael J. Wysocki wrote:
>>>> On Wednesday, September 10, 2014 03:15:08 PM Anup Chenthamarakshan wrote:
>>>>>
>>>>> Tools like powertop and turbostat are not present by default on all systems,
>>>>> so it is not always possible to use them :(
>>>>
>>>> Which systems are you referring to in particular?
>>>
>>> We're testing on Chrome OS devices (Chromebooks).
>>
>> How big of a deal is it to install the tools mentioned above on such a system?
>>
>> At least turbostat is shipped with the kernel source.
>
> Given the web browser based front end of Chrome OS, installing these
> tools will only get us so far -- if the system is in developer mode,
> the tools are accessible but when the system is in normal (verified
> boot mode) these tools cannot be launched directly.
>
> We are in the process of switching Chrome OS x86 kernels from ondemand
> governor to intel_pstate.  When debugging power consumption issues,
> losing the ability to easily get CPU frequency related information as
> a side-effect of this switch is less than ideal.
>
> We are happy to spin this patch to expose aperf/mperf based CPU
> frequency information if you think that is the better route to take
> longer term.

You can get the frequency as measured by intel_pstate from /proc/cpuinfo
or /sys/devices/system/cpu/cpu[n]/cpufreq/cpuinfo_cur_freq but his is only
for the most recent sample on cpu[n]

reading MSR 0x199 and some reasonable rate will let you graph what request
is being made on each core.

>
>>
>> --
>> I speak only for myself.
>> Rafael J. Wysocki, Intel Open Source Technology Center.
>
>
>

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