From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757585AbYEJTST (ORCPT ); Sat, 10 May 2008 15:18:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754032AbYEJTSJ (ORCPT ); Sat, 10 May 2008 15:18:09 -0400 Received: from yw-out-2324.google.com ([74.125.46.28]:25908 "EHLO yw-out-2324.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752804AbYEJTSG (ORCPT ); Sat, 10 May 2008 15:18:06 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:mime-version:content-type:content-transfer-encoding:content-disposition; b=Bck9H1VUZtOUQRHtwEu0yf6cMrNkYKsxFHVjstFLbvWNZRE0Kj+uYb2hxry/LW1JuvraXg46S1HIbjpNNk2FdLDQ2JG7ORVe21C6WhwXKgcRjt1p3wbB42BIOUsveqZNbtu6ieM7tN4DBOYGMPlOOyz15mxtUTijN1N30lOnNEI= Message-ID: Date: Sat, 10 May 2008 21:18:04 +0200 From: Matthew To: "Ingo Molnar" Subject: performance "regression" in cfq compared to anticipatory, deadline and noop Cc: "Linux Kernel Mailing List" MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ingo, hi everybody, I've encountered sort of a performance "regression" in using cfq (and the cfq-based bfq) in comparison with the other io-schedulers: 1) interactivity during load is much better compared to the others (thanks a lot for that, that made me appreciate this scheduler) BUT 2) everything seems to take somewhat longer to load (big applications like firefox, etc. ) 3) hdparm shows the same behavior since I've started using cfq only for a few days (approx. 1-2 weeks now) I didn't really notice it until I tested "performance" via hdparm: /dev/sdd: Timing buffered disk reads: 308 MB in 3.01 seconds = 102.22 MB/sec /dev/sdd: Timing buffered disk reads: 306 MB in 3.01 seconds = 101.66 MB/sec /dev/sdd: Timing buffered disk reads: 304 MB in 3.02 seconds = 100.77 MB/sec noop [anticipatory] deadline cfq deadline & noop are similar, the test of noop finishes pretty fast ... /dev/sdd: Timing buffered disk reads: 170 MB in 3.02 seconds = 56.27 MB/sec /dev/sdd: Timing buffered disk reads: 176 MB in 3.02 seconds = 58.21 MB/sec /dev/sdd: Timing buffered disk reads: 176 MB in 3.02 seconds = 58.22 MB/sec noop anticipatory deadline [cfq] this behavior occurs on an jmicron sata-controller (JMB363/361) and the probably the 4th port of the Intel ICH7R but only with cfq selected, the first (?) and second (?) port of the Intel ICH7R are fine performance-wise, don't know why it's that picky with the other schedulers it's fine I've tested: 2.6.24-gentoo-r7 (+ 2.6.24.7), 2.6.24-gentoo-r3, 2.6.25, 2.6.25.2 (+ 2.6.25-zen1), 2.6.25-rc8, the kernel of the ubuntu desktop-livecd amd64 (ubuntu 8.04) (cfq enabled) all show this worse "performance" compared to the other schedulers all kernels are amd64 on gentoo ~amd64, glibc-2.7.1, gcc-4.2.3 hardened hardware: Asus P5W DH Deluxe I unfortuantely can't test earlier kernel-versions due to the fact that I'm using reiser4 for /(root) and the earlier kernels + reiser4 aren't that stable in terms of data safety hopefully this is reproducable & you guys can explain if this is something to "worry" about (performance) and/or a real regression or just some kind of placebo effect Many thanks in advance & thanks a lot for this great scheduler (cfq; I'm looking forward to bfq in mainline which seems to work even better under load) Regards Mat