From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762295AbXKNRxu (ORCPT ); Wed, 14 Nov 2007 12:53:50 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757202AbXKNRx2 (ORCPT ); Wed, 14 Nov 2007 12:53:28 -0500 Received: from pentafluge.infradead.org ([213.146.154.40]:52230 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753606AbXKNRx1 (ORCPT ); Wed, 14 Nov 2007 12:53:27 -0500 Date: Wed, 14 Nov 2007 09:51:51 -0800 From: Arjan van de Ven To: Ingo Molnar Cc: Andrew Morton , "Alan D. Brunelle" , Rik van Riel , jens.axboe@oracle.com, linux-kernel@vger.kernel.org Subject: Re: [patch] Give kjournald a IOPRIO_CLASS_RT io priority Message-ID: <20071114095151.43c5e576@laptopd505.fenrus.org> In-Reply-To: <20071114171805.GA20959@elte.hu> References: <20071015104647.14e60bc5@laptopd505.fenrus.org> <20071015114738.6b5a25c7.akpm@linux-foundation.org> <20071015161315.4fe18e07@bree.surriel.com> <20071015141236.62b075c6.akpm@linux-foundation.org> <473B18BA.5000709@hp.com> <20071114091451.d4b110db.akpm@linux-foundation.org> <20071114171805.GA20959@elte.hu> Organization: Intel X-Mailer: Claws Mail 3.0.2 (GTK+ 2.12.1; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 14 Nov 2007 18:18:05 +0100 Ingo Molnar wrote: > > * Andrew Morton wrote: > > > ooh, more performance testing. Thanks > > > > > * The overwriter task (on an 8GiB file), average over 10 runs: > > > o 2.6.24 - 300.88226 seconds > > > o 2.6.24 + Arjan's patch - 403.85505 seconds > > > > > > * The read-a-different-kernel-tree task, average over 10 runs: > > > o 2.6.24 - 46.8145945549 seconds > > > o 2.6.24 + Arjan's patch - 39.6430601119 seconds > > > > > > * The large-linear-read task (on an 8GiB file), average over > > > 10 runs: o 2.6.24 - 290.32522 seconds > > > o 2.6.24 + Arjan's patch - 386.34860 seconds > > > > These are *large* differences, making this a very signifcant > > patch. Much care is needed now. > > and the numbers suggest it's mostly a severe performance regression. > That's not what i have expected - ho hum. Apologies for my earlier > "please merge it already!" whining. that's.. not automatic; it depends on what the right thing is :-( What for sure changes is that who gets to do IO changes. Some of the tests we ran internally (we didn't publish yet because we saw REALLY large variations for most of them even without any patch) show for example that "dbench" got slower. But.. dbench gets slower when things get more fair, and faster when things get unfair. What conclusion you draw out of that is a whole different matter and depends on exactly what the test is doing, and what is the right thing for the OS to do in terms of who gets to do the IO. THis makes the patch more tricky than the one line change suggests, and this is also why I haven't published a ton of data yet; it's hard to get useful tests for this (and the variation of the 2.6.23+ kernels makes it even harder to do anything meaningful ;-( ) -- If you want to reach me at my work email, use arjan@linux.intel.com For development, discussion and tips for power savings, visit http://www.lesswatts.org