From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754337AbXKNTqH (ORCPT ); Wed, 14 Nov 2007 14:46:07 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757062AbXKNTpz (ORCPT ); Wed, 14 Nov 2007 14:45:55 -0500 Received: from g5t0007.atlanta.hp.com ([15.192.0.44]:2641 "EHLO g5t0007.atlanta.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753743AbXKNTpy (ORCPT ); Wed, 14 Nov 2007 14:45:54 -0500 X-Greylist: delayed 530 seconds by postgrey-1.27 at vger.kernel.org; Wed, 14 Nov 2007 14:45:54 EST Message-ID: <473B4FE5.7000601@hp.com> Date: Wed, 14 Nov 2007 14:43:33 -0500 From: "Alan D. Brunelle" User-Agent: Thunderbird 2.0.0.6 (X11/20071022) MIME-Version: 1.0 To: Arjan van de Ven Cc: Ingo Molnar , Andrew Morton , Rik van Riel , jens.axboe@oracle.com, linux-kernel@vger.kernel.org Subject: Re: [patch] Give kjournald a IOPRIO_CLASS_RT io priority 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> In-Reply-To: <20071114095151.43c5e576@laptopd505.fenrus.org> Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Arjan van de Ven wrote: > 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 ;-( ) > > > I'd also like to point out here that the run-to-run deviation was indeed quite large for both the unpatched- and patched-kernels, I'll report on that information with the next set of results... Alan