linux-kernel - Re: [PATCH 7/7] ondemand: Solve the big performance issue with ondemand during disk IO

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Date:	Fri, 23 Apr 2010 09:06:48 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Pavel Machek <pavel@....cz>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	mingo@...e.hu, peterz@...radead.org, tglx@...utronix.de,
	davej@...hat.com, cpufreq@...r.kernel.org
Subject: Re: [PATCH 7/7] ondemand: Solve the big performance issue with
 ondemand during disk IO

On Fri, 23 Apr 2010 10:38:28 +0200
Pavel Machek <pavel@....cz> wrote:

> On Fri 2010-04-23 06:52:48, Arjan van de Ven wrote:
> > On Fri, 23 Apr 2010 07:24:39 +0200
> > Pavel Machek <pavel@....cz> wrote:
> > 
> > > 
> > > Well, and now, if you do something like cat /dev/<your usb1.1
> > > hdd> > /dev/null, you'll keep cpu on max frequency. Not a problem
> > > hdd> > for new
> > > core i7, but probably big deal for athlon 64.
> > 
> > do you have facts not speculation for this? Does the athlon 64
> > really
> 
> You want the patch applied, you should be able to justify it.

You make a claim... all I am asking if you are doing just random guess
or basing this on facts.

The machines I have access to don't show any impact during actual idle,
because they stop clocks and generally even lower the voltage. 
You make a claim that a certain machine does not do either... all I'm
asking if that claim is based on data or on speculation.

> 
> > keep its voltage high during idle? That would surprise me greatly...
> > (and if it does, does it matter? the clock is stopped anyway there)
> 
> Yes, I believe it keeps voltage up, and as a leakage is big part of
> power consumption there, stopped clocks will not help much.

again do you have actual data? 

 
> I believe you are developing on wrong machine. Seems like core i7 just
> wants max frequency, all the time. Older designs were not like that.
> 
> Do you have early intel speedstep machine near you?

oh I use many different machines. the intel machines at least stop the
clocks, and for a really long time also lower the frequency in idle.
(especially during deeper C states, but even during C1)

> 
> > the only place where my patch makes a real difference is when the
> > cpu is idle due to blocking IO! So do you have data that the athlon
> > 64 gets too hot if you select a high frequency during an idle
> > period, where the clock is already stopped?
> 
> iirc even idle power consumption was much higher when on max
> voltage... I'll get some numbers from my old notes; I no longer have
> the hw.

make sure it's data based on tickless... without tickless we were never
really idle ;-(



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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