From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S274879AbTGaV1l (ORCPT ); Thu, 31 Jul 2003 17:27:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S274880AbTGaV1l (ORCPT ); Thu, 31 Jul 2003 17:27:41 -0400 Received: from fw.osdl.org ([65.172.181.6]:13721 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S274879AbTGaV1Q convert rfc822-to-8bit (ORCPT ); Thu, 31 Jul 2003 17:27:16 -0400 Date: Thu, 31 Jul 2003 14:15:17 -0700 From: Andrew Morton To: mru@users.sourceforge.net (=?ISO-8859-1?Q?M=E5ns_Rullg=E5rd?=) Cc: linux-kernel@vger.kernel.org Subject: Re: Disk performance degradation Message-Id: <20030731141517.0ceccc77.akpm@osdl.org> In-Reply-To: References: <20030729182138.76ff2d96.lista1@telia.com> <3F26A5E2.4070701@aros.net> X-Mailer: Sylpheed version 0.9.4 (GTK+ 1.2.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org mru@users.sourceforge.net (Måns Rullgård) wrote: > > Mike Dresser writes: > > > Probably for reasons like that. For some reason, I can't set my ICH4 > > based controller(ASUS P4B533) and Quantum Fireball AS40.0 to more than > > 255. Kernel is 2.4.21 > > It appears that in 2.[56] kernels the unit for readahead is bytes, > rather than sectors, as used in 2.4 kernels. The ioctl which is used by blockdev --setra is still in 512-byte units. There are other backdoors such as IDE-private /proc files which can be used to set readahead. I'm not sure what units they use, and I don't know what mechanism hdparm is using to diddle readahead. Whatever it is, I suggest you ignore it and use /sbin/blockdev; it works for all disk types.