From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S265132AbUEYV6l (ORCPT ); Tue, 25 May 2004 17:58:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S265140AbUEYV6B (ORCPT ); Tue, 25 May 2004 17:58:01 -0400 Received: from fw.osdl.org ([65.172.181.6]:47238 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S265132AbUEYV4o (ORCPT ); Tue, 25 May 2004 17:56:44 -0400 Date: Tue, 25 May 2004 14:59:23 -0700 From: Andrew Morton To: olh@suse.de, linux-kernel@vger.kernel.org Subject: Re: very low performance on SCSI disks if device node is in tmpfs Message-Id: <20040525145923.68af0ad8.akpm@osdl.org> In-Reply-To: <20040525144836.1af59a96.akpm@osdl.org> References: <20040525184732.GB26661@suse.de> <20040525144836.1af59a96.akpm@osdl.org> X-Mailer: Sylpheed version 0.9.7 (GTK+ 1.2.10; i586-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton wrote: > > Olaf Hering wrote: > > > > Any ideas why the location of the device node makes such a big > > difference? I always wondered why my firewire is so dog slow with 2.6. > > Now I know the reason: /dev is in tmpfs. > > I dont see that with IDE disks, only with SCSI. > > This is truly bizarre. It affects IDE too - the context switch and interrupt rates are through the roof. IDE disks have always seemed better at doing readahead, which is why the transfer bandwidth is much the same. Everything there is consistent with "not doing readahead". The fickle finger points in the general direction of fs/block_dev.c:do_open(). Later.