From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S265729AbUBLJmS (ORCPT ); Thu, 12 Feb 2004 04:42:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266077AbUBLJmS (ORCPT ); Thu, 12 Feb 2004 04:42:18 -0500 Received: from denise.shiny.it ([194.20.232.1]:10958 "EHLO denise.shiny.it") by vger.kernel.org with ESMTP id S265729AbUBLJmR (ORCPT ); Thu, 12 Feb 2004 04:42:17 -0500 Message-ID: X-Mailer: XFMail 1.4.7 on Linux X-Priority: 3 (Normal) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8bit MIME-Version: 1.0 In-Reply-To: <20040212022314.GS4478@dualathlon.random> Date: Thu, 12 Feb 2004 10:42:15 +0100 (CET) From: Giuliano Pochini To: Andrea Arcangeli Subject: Re: ext2/3 performance regression in 2.6 vs 2.4 for small interl Cc: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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. -- Giuliano.