From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261784AbUBNPAf (ORCPT ); Sat, 14 Feb 2004 10:00:35 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261973AbUBNPAf (ORCPT ); Sat, 14 Feb 2004 10:00:35 -0500 Received: from columba.eur.3com.com ([161.71.171.238]:32470 "EHLO columba.eur.3com.com") by vger.kernel.org with ESMTP id S261784AbUBNPAe (ORCPT ); Sat, 14 Feb 2004 10:00:34 -0500 Message-ID: <402E380B.8070806@jburgess.uklinux.net> Date: Sat, 14 Feb 2004 15:00:27 +0000 From: Jon Burgess User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.6) Gecko/20040113 X-Accept-Language: en-gb, en-us, en MIME-Version: 1.0 To: Andrew Morton CC: Jon Burgess , linux-kernel@vger.kernel.org Subject: Re: ext2/3 performance regression in 2.6 vs 2.4 for small interleaved writes References: <402A7CA0.9040409@jburgess.uklinux.net> <20040212015626.48631555.akpm@osdl.org> In-Reply-To: <20040212015626.48631555.akpm@osdl.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton wrote: >So you'll see that instead of a single full-bandwidth >write, we do two half-bandwidth writes. If it weren't for disk writeback >caching, it would be as much as 4x slower. > Write caching does indeed make a big difference. Here is a test run on a drive with and without write caching (hdparm -W 0/1). The test was done on 2.6.2 with ext3 and shows the write speed in MB/s: Write Cache 1 Stream 2 Streams Enabled 21.54 3.66 Disabled 18.11 0.46 The two stream case is almost 10x slower without write caching. I don't think this explains the difference between 2.4 and 2.6 unless one of them changes the write cache mode of the drive. Jon