linux-kernel - Re: [PATCH 3/7] cpufreq: intel_pstate: Add debugfs file stats

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Date:	Tue, 10 Jun 2014 19:21:12 +0300
From:	Stratos Karafotis <stratosk@...aphore.gr>
To:	Dirk Brandewie <dirk.brandewie@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Dirk Brandewie <dirk.j.brandewie@...el.com>
CC:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/7] cpufreq: intel_pstate: Add debugfs file stats

On 10/06/2014 06:47 μμ, Dirk Brandewie wrote:
> On 06/09/2014 02:00 PM, Stratos Karafotis wrote:
>> Add stats file in debugfs under driver's parent directory
>> (pstate_snb) which counts the time in nsecs per requested
>> P state and the number of times the specific state
>> was requested.
>>
>> The file presents the statistics per logical CPU in the
>> following format. The time is displayed in msecs:
>>
> 
> NAK
> 
> This adds significantly to the memory footprint to gather information
> that is available by post processing the perf tracepoint information.
> The increase isn't horrible on single socket desktop processor machines
> but gets big with server class machines.  One vendor I have talked to considers
> a machine with 1024 cpus to be a SMALL machine.
> 

If I am not wrong the sizeof pstate_stat is 20B. On my CPU with 20 P states, we
need 400B per logical CPU (3200B total in my desktop) plus 64B for stats pointers.

In your example this would need about 400KB - 500KB?
Is it too much for 1024 a CPUs system?

I think it's a useful piece of info that we can have it directly without
post processing tracepoint.
Is it acceptable to conditionally compile it with a new CONFIG option?


Thanks,
Stratos

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