linux-kernel - Re: [PATCH 3/5] scheduler: cpuacct: Enable platform hooks to track cpuusage for CPU frequencies

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Date:	Mon, 22 Nov 2010 13:23:06 +0100
From:	Florian Mickler <florian@...kler.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	John Stultz <john.stultz@...aro.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Mike Chan <mike@...roid.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 3/5] scheduler: cpuacct: Enable platform hooks to track
 cpuusage for CPU frequencies

On Mon, 22 Nov 2010 11:43:59 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> On Mon, 2010-11-22 at 06:51 +0100, Florian Mickler wrote:
> > On Sat, 20 Nov 2010 11:48:24 +0100
> > Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > On Fri, 2010-11-19 at 18:08 -0800, John Stultz wrote:
> > > > From: Mike Chan <mike@...roid.com>
> > > > 
> > > > Introduce new platform callback hooks for cpuacct for tracking CPU frequencies
> > > > 
> > > > Not all platforms / architectures have a set CPU_FREQ_TABLE defined
> > > > for CPU transition speeds. In order to track time spent in at various
> > > > CPU frequencies, we enable platform callbacks from cpuacct for this accounting.
> > > > 
> > > > Architectures that support overclock boosting, or don't have pre-defined
> > > > frequency tables can implement their own bucketing system that makes sense
> > > > given their cpufreq scaling abilities.
> > > > 
> > > > New file:
> > > > cpuacct.cpufreq reports the CPU time (in nanoseconds) spent at each CPU
> > > > frequency.
> > > 
> > > I utterly detest all such accounting crap.. it adds ABI constraints it
> > > add runtime overhead. etc.. 
> > > 
> > > Can't you get the same information by using the various perf bits? If
> > > you trace the cpufreq changes you can compute the time spend in each
> > > power state, if you additionally trace the sched_switch you can compute
> > > it for each task.
> > > 
> > > 
> > This is probably used for "on-site" debugging of production systems.
> 
> Dude, its from the _android_ tree... its cpufreq crud.. it must be some
> crack induced power management scheme.
> 
> 

:) 

what I wanted to get at, was that they probably need these stats
aggregated somewhere neat and tidy and can not compute them on the fly
recording massive amounts of data...

I wonder why they didn't put this in the
idle-driver.  I don't know. 

Regards,
Flo

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