linux-kernel - Re: [patch 2/2] x86: Manage ENERGY_PERF

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Date:	Fri, 5 Mar 2010 21:40:29 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Cc:	Randy Dunlap <rdunlap@...otime.net>, Ingo Molnar <mingo@...e.hu>,
	H Peter Anvin <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Len Brown <lenb@...nel.org>, Dave Jones <davej@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [patch 2/2] x86: Manage ENERGY_PERF_BIAS based on cpufreq
 governor

Hi!

> >You should say what the setting does; you can mention below what MSR
> >it corresponds to, but "Control IA32_ENERGY_PERF_BIAS setting" is not
> >suitable user documentation.
> >
> >> Also, the expectation here is that kernel will do the right thing by
> >> default. The option here is to the user who_knows_what_he_is_doing to
> >> override the kernel default.
> >
> >You did not give user enough information to do anything intelligent...
> 
> I have rephrased it in the newer version sent yday with more info.

Good.

> >> > Also... does it make change to tweak the setting during 
> >runtime? Maybe
> >> > different settings for AC and battery power?
> >> 
> >> Yes. Matthew mentioned in other response aboue setting this based on
> >> freq. For the CPUs that support this feature currently, we don't see
> >> advantage in setting this feature at run time.
> >
> >If the feature is useless, then why set it at all?
> 
> I just said changing it at run time doesn't give us benefits. Not
>that

That can be only true if it does not give benefits period... AC and
battery power are quite different scenarios.

> the feature is useless. Having the default value for the tunable in
> mid-range does increase energy-efficiency than the tunable being
> at performance level.

So... what does it really do? What is the difference in power
consumption, and what is the difference in performance?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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