From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756185AbZA2UrU (ORCPT ); Thu, 29 Jan 2009 15:47:20 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751754AbZA2UrL (ORCPT ); Thu, 29 Jan 2009 15:47:11 -0500 Received: from e32.co.us.ibm.com ([32.97.110.150]:44842 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751404AbZA2UrJ (ORCPT ); Thu, 29 Jan 2009 15:47:09 -0500 Message-ID: <498215C9.6090208@felter.org> Date: Thu, 29 Jan 2009 14:47:05 -0600 From: Wes Felter User-Agent: Thunderbird 2.0.0.18 (Macintosh/20081105) MIME-Version: 1.0 To: dingxn@ymail.com CC: linux-kernel@vger.kernel.org Subject: Re: a question about p4_clockmod module on Xeon quad core processors References: <765076.76058.qm@web59913.mail.ac4.yahoo.com> In-Reply-To: <765076.76058.qm@web59913.mail.ac4.yahoo.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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