linux-kernel - Re: a question about p4_clockmod module on Xeon quad core processors

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Message-ID: <20090129195447.GA14636@redhat.com>
Date:	Thu, 29 Jan 2009 14:54:47 -0500
From:	Dave Jones <davej@...hat.com>
To:	Xiaoning Ding <dingxn@...il.com>
Cc:	Michael Tokarev <mjt@....msk.ru>, linux-kernel@...r.kernel.org
Subject: Re: a question about p4_clockmod module on Xeon quad core
	processors

On Thu, Jan 29, 2009 at 11:40:25AM -0800, Xiaoning Ding wrote:

 > Thanks for the explanation. So the conclusion is that ACPI-cpufreq
 > can reduce power consumption by lowering cpu frequencies, and
 > p4-clockmod can hardly save power because CPU frequences are not
 > changed.

yes. and also that it inhibits entering deeper C states for longer periods.

 > My experiments do not consider power consumption. It only requires to
 > slow down the speed of some cores by either reducing frequencies or
 > clock modulation. In such case, p4-clockmod is still a good choice for
 > me. Can anyone give me some hints on whether p4-clockmod works on Xeon
 > quad-core processors, and how to get it work?

I'm not sure if the registers are still there on quad cores, but I
would be surprised if they weren't.  Hitting them directly with
msr tools is probably the best way, or writing a small program
that manipulates /dev/cpu/*/msr directly.

	Dave

-- 
http://www.codemonkey.org.uk
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