From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752805Ab0DSNls (ORCPT ); Mon, 19 Apr 2010 09:41:48 -0400 Received: from casper.infradead.org ([85.118.1.10]:36686 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751558Ab0DSNlq convert rfc822-to-8bit (ORCPT ); Mon, 19 Apr 2010 09:41:46 -0400 Date: Mon, 19 Apr 2010 06:43:25 -0700 From: Arjan van de Ven To: =?UTF-8?B?w4lyaWM=?= Piel Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mingo@elte.hu, peterz@infradead.org, tglx@linutronix.de, davej@redhat.com, cpufreq@vger.kernel.org Subject: Re: [PATCH 7/7] ondemand: Solve the big performance issue with ondemand during disk IO Message-ID: <20100419064325.49cb3108@infradead.org> In-Reply-To: <4BCC147B.10708@tremplin-utc.net> References: <20100418115949.7b743898@infradead.org> <20100418120346.1b478410@infradead.org> <4BCC147B.10708@tremplin-utc.net> Organization: Intel X-Mailer: Claws Mail 3.7.5 (GTK+ 2.16.6; i586-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 19 Apr 2010 10:29:47 +0200 Éric Piel wrote: > > > > The problem and fix are both verified with the "perf timechar" tool. > Hi, > I don't doubt that keeping the cpu full frequency during IO can > improve some specific workloads, however in your log message you > don't explain how much we are loosing. first of all, it's so bad that people will just turn the whole power management off... at which point fixing the really bad bug is actually quite a win > > How much more energy is consumed when doing a "updatedb" or "find /" ? on the machines I used this on (Core i7's) it's actually hardly measurable. All CPUs I have access to turn the voltage entirely off during idle, so while the frequency is higher, if you're mostly IO bound, it's only for very short durations... while still being mostly "off". -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org