linux-kernel - Re: [PATCH v3 1/3] cpufreq: ondemand: Change the calculation of target frequency

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Date:	Mon, 10 Jun 2013 00:11:04 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Stratos Karafotis <stratosk@...aphore.gr>,
	Borislav Petkov <bp@...e.de>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-pm@...r.kernel.org,
	cpufreq@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] cpufreq: ondemand: Change the calculation of target frequency

On Sunday, June 09, 2013 11:14:49 PM Borislav Petkov wrote:
> On Sun, Jun 09, 2013 at 10:58:51PM +0200, Rafael J. Wysocki wrote:
> > Can you possibly prepare a graph showing both the execution time
> > and energy consumption for several different loop durations in your
> > program (let's keep the 5000 us sleep for now), including multiples of
> > sampling_rate as well as some other durations?
> 
> Judgind by the times in C0 one of the cores spent, this small program
> is single-threaded and is a microbenchmark.

Yes, it is single-threaded, but that can be easily addressed by running
multiple copies of it in parallel. :-)

And yes, it is a microbenchmark, ->

> And you know how optimizing against a microbenchmark doesn't really make
> a lot of sense.

-> but this is more about finding possible issues that about optimizing.

I'm regarding this change as a substantial code simplification in the first
place, both in terms of conceptual complexity and the actual code size, so I'd
like to know what is *likely* to be affected by it (be it a microbenchmark or
whatever).

IOW, try to play a devil's advocate and find something that get's worse after
applying these changes.  If we can't find anything like that, there won't be
any reason not to apply them.

> I wonder if lmbench or aim9 or whatever would make more sense to try here...

I think we'll need to try them too.

Thanks,
Rafael


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