Date: Mon, 22 Nov 2010 06:51:29 +0100
From: Florian Mickler <florian@mickler.org>
To: Peter Zijlstra <peterz@infradead.org>
Newsgroups: gmane.linux.kernel
Cc: John Stultz <john.stultz@linaro.org>, lkml <linux-kernel@vger.kernel.org>,
        Mike Chan <mike@android.com>, Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH 3/5] scheduler: cpuacct: Enable platform hooks to track
 cpuusage for CPU frequencies
Message-ID: <20101122065129.072bba06@schatten.dmk.lab>
In-Reply-To: <1290250104.2118.4.camel@laptop>
References: <1290218934-8544-1-git-send-email-john.stultz@linaro.org>
	<1290218934-8544-4-git-send-email-john.stultz@linaro.org>
	<1290250104.2118.4.camel@laptop>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1858
Lines: 47

On Sat, 20 Nov 2010 11:48:24 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, 2010-11-19 at 18:08 -0800, John Stultz wrote:
> > From: Mike Chan <mike@android.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.

I.e. when someone sends them a problem report using an
bugreport-tool, they gather all useful information they can get on the
system because they only have one-way communication with their bug
reporters.

Do the perf bits work for such a usecase? If I guess correctly, the
perf bits need a userspace part that computes what would be in the
cpuacct.cpufreq file? 

Regards,
Flo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/