linux-kernel - Re: [PATCH][RFC] Adding transition of CPU frequency counting support to perfcounters

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Message-ID: <20090802201321.GH24486@elte.hu>
Date:	Sun, 2 Aug 2009 22:13:21 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>
Cc:	a.p.zijlstra@...llo.nl, fweisbec@...il.com, linux@...do.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC] Adding transition of CPU frequency counting
	support to perfcounters


* Hitoshi Mitake <mitake@....info.waseda.ac.jp> wrote:

> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Subject: Re: [PATCH][RFC] Adding transition of CPU frequency counting support to perfcounters
> Date: Sat, 18 Jul 2009 18:09:15 +0200
> 
> > On Sat, 2009-07-18 at 23:11 +0900, mitake@....info.waseda.ac.jp wrote:
> > > 
> > > Oh, my perf could count cpufreq events!
> > > Thanks for your nice advice!
> > > 
> > > % perf stat -a sleep 60
> > > 
> > >  Performance counter stats for 'sleep 60':
> > > 
> > >   479088.075595  task-clock-msecs         #      7.984 CPUs
> > >          199080  context-switches         #      0.000 M/sec
> > >           19584  CPU-migrations           #      0.000 M/sec
> > >          322978  page-faults              #      0.001 M/sec
> > >              29  cpufreq-up               #      0.000 M/sec
> > >              42  cpufreq-down             #      0.000 M/sec
> > >     73703367828  cycles                   #    153.841 M/sec
> > >     52005203450  instructions             #      0.706 IPC
> > >       209762467  cache-references         #      0.438 M/sec
> > >        84916856  cache-misses             #      0.177 M/sec
> > > 
> > >    60.009508200  seconds time elapsed
> > > 
> > > And I'm using ondemand governor now,
> > > so kernel thread [kondemand] context causes freq transition.
> > > I didn't notice that...
> > > 
> > > Could you merge this patch?
> > > Can I send this patch with descriptions and Signed-off-by?
> > 
> > Why, what is the usecase?
> > 
> > 
> 
> Hmm, I considered, and I noticed that this patch makes no sense. 
> Because my first purpose "collecting CPU freq transitions per 
> process level" is completely nonsense. CPU freq transitions are 
> global things, not one of processes.

Well, but 'perf stat -a' will install per CPU counters, i.e. the 
counting is global, not per task.

(even per task counting makes a certain amount of sense: which apps 
generate the most freq change events for example?)

	Ingo
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