Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758580AbZA2TzN (ORCPT ); Thu, 29 Jan 2009 14:55:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751610AbZA2Ty6 (ORCPT ); Thu, 29 Jan 2009 14:54:58 -0500 Received: from mx2.redhat.com ([66.187.237.31]:33763 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751787AbZA2Ty5 (ORCPT ); Thu, 29 Jan 2009 14:54:57 -0500 Date: Thu, 29 Jan 2009 14:54:47 -0500 From: Dave Jones To: Xiaoning Ding Cc: Michael Tokarev , linux-kernel@vger.kernel.org Subject: Re: a question about p4_clockmod module on Xeon quad core processors Message-ID: <20090129195447.GA14636@redhat.com> Mail-Followup-To: Dave Jones , Xiaoning Ding , Michael Tokarev , linux-kernel@vger.kernel.org References: <20090129172406.GB14096@redhat.com> <279321.76517.qm@web59906.mail.ac4.yahoo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <279321.76517.qm@web59906.mail.ac4.yahoo.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1221 Lines: 29 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/