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Date: Thu, 29 Jan 2009 17:12:06 -0800 (PST)
From: Xiaoning Ding <dingxn@ymail.com>
Reply-To: dingxn@ymail.com
Subject: Re: a question about p4_clockmod module on Xeon quad core processors
To: Wes Felter <wesley@felter.org>
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <498215C9.6090208@felter.org>
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It works on my machine. Thanks for the help!

Xiaoning


--- On Thu, 1/29/09, Wes Felter <wesley@felter.org> wrote:

> From: Wes Felter <wesley@felter.org>
> Subject: Re: a question about p4_clockmod module on Xeon quad core processors
> To: dingxn@ymail.com
> Cc: linux-kernel@vger.kernel.org
> Date: Thursday, January 29, 2009, 8:47 PM
> This will give you an effective speed of 250 MHz:
> 
> for cpu in 0 1 2 3; do
> 	cpufreq-set -c $cpu -g userspace
> 	cpufreq-set -c $cpu -u 2.0GHz
> 	wrmsr -p $cpu 0x19A 0x12
> done
> 
> 0x19A is the IA32_CLOCK_MODULATION MSR and 0x12 is
> calculated from the Intel 64 and IA-32 Architectures
> Software Developer’s Manual section 13.5.3. Legal MSR
> values are 0x12 (12.5% duty cycle) - 0x1E (87.5%) or 0x00
> for 100%. I tested it on a quad-core Xeon and it works.
> 
> This is somewhat reckless, so use it with caution.
> 
> Wes Felter - wesley@felter.org


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