From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762589AbXKNS4i (ORCPT ); Wed, 14 Nov 2007 13:56:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760743AbXKNS4X (ORCPT ); Wed, 14 Nov 2007 13:56:23 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:34629 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760432AbXKNS4W (ORCPT ); Wed, 14 Nov 2007 13:56:22 -0500 Date: Wed, 14 Nov 2007 19:55:26 +0100 From: Ingo Molnar To: Arjan van de Ven 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: <20071114185526.GB4943@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> <20071114095151.43c5e576@laptopd505.fenrus.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071114095151.43c5e576@laptopd505.fenrus.org> User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.1.7-deb -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Arjan van de Ven wrote: > > > > * 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. yeah, i'd agree to not too much faith into dbench results. Ingo