From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266481AbUBLO7o (ORCPT ); Thu, 12 Feb 2004 09:59:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266488AbUBLO7o (ORCPT ); Thu, 12 Feb 2004 09:59:44 -0500 Received: from ppp-217-133-42-200.cust-adsl.tiscali.it ([217.133.42.200]:36237 "EHLO dualathlon.random") by vger.kernel.org with ESMTP id S266481AbUBLO7m (ORCPT ); Thu, 12 Feb 2004 09:59:42 -0500 Date: Thu, 12 Feb 2004 15:59:41 +0100 From: Andrea Arcangeli To: Giuliano Pochini Cc: linux-kernel@vger.kernel.org Subject: Re: ext2/3 performance regression in 2.6 vs 2.4 for small interl Message-ID: <20040212145940.GU4478@dualathlon.random> References: <20040212022314.GS4478@dualathlon.random> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i X-GPG-Key: 1024D/68B9CB43 13D9 8355 295F 4823 7C49 C012 DFA1 686E 68B9 CB43 X-PGP-Key: 1024R/CB4660B9 CC A0 71 81 F4 A0 63 AC C0 4B 81 1D 8C 15 C8 E5 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 12, 2004 at 10:42:15AM +0100, Giuliano Pochini wrote: > > On 12-Feb-2004 Andrea Arcangeli wrote: > > > the main difference is that 2.4 isn't in function of time, it's in > > function of requests, no matter how long it takes to write a request, > > so it's potentially optimizing slow devices when you don't care about > > latency (deadline can be tuned for each dev via > > /sys/block/*/queue/iosched/). > > IMHO it's the opposite. Transfer speed * seek time of some > slow devices is lower than fast devices. For example: > > Hard disk raw speed= 40MB/s seek time = 8ms > MO/ZIP raw speed= 3MB/s seek time = 25ms > > One seek of HD costs about 320KB, while on a slow drive it's > only 75KB. 2.4 has a terrible latency on slow devices, and it > has very small advantage in terms of speed. On CDs and DVDs > the cost of a seek is much higher, but since the data is > usually accessed sequentially you have the high latency > penalty with no appreciable speed gain in this case too. I was thinking at old slow harddisks (5M/sec), and I don't think all data on cds is always accessed sequentially, you only need two tasks reading two files.