From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 24 Sep 2001 12:40:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 24 Sep 2001 12:40:28 -0400 Received: from islay.mach.uni-karlsruhe.de ([129.13.162.92]:8628 "EHLO mailout.plan9.de") by vger.kernel.org with ESMTP id ; Mon, 24 Sep 2001 12:40:06 -0400 Date: Mon, 24 Sep 2001 18:40:08 +0200 From: To: Nicholas Knight Cc: Matthias Andree , linux-kernel@vger.kernel.org, reiserfs-list@namesys.com Subject: Re: [reiserfs-list] Re: [PATCH] 2.4.10 improved reiserfs a lot, but could still be better Message-ID: <20010924184008.A4126@schmorp.de> Mail-Followup-To: Nicholas Knight , Matthias Andree , linux-kernel@vger.kernel.org, reiserfs-list@namesys.com In-Reply-To: <20010924173210.A7630@emma1.emma.line.org> <20010924161518.KYHD11251.femail27.sdc1.sfba.home.com@there> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20010924161518.KYHD11251.femail27.sdc1.sfba.home.com@there> X-Operating-System: Linux version 2.4.8-ac9 (root@cerebro) (gcc version 3.0.1) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 24, 2001 at 09:15:19AM -0700, Nicholas Knight wrote: [turning off write-cache] > I'm sorry, but that's not acceptable. (I had it turned off for a long time, until I reasoned: real power-outages are very rare, so I can leave it turned on anyways and risk a filesystemcheck after outages). The reason this kills performance ALWAYS is that ide does not support large enough transfer sizes (8-32k on most drives) to fill one track. Turning off write caching has a big chance of lowering your transaction throughput to the drive's RPM. Combined with linux' not-that-optimal elevator and write behaviour this has good chances of costing a lot of performance. TCQ will obviously help, but I somehow doubt it will work fine - even with SCSI TCQ is a nightmare (the aic7xxx drive regularly kills my system if tagged queueing is enabled for example). IDE currently is a mess (I do _not_ expect my drive performance to simply halve just because two devices to share the bus, even if this is how conservative ide is destined to work). I am convinced that there is a way of creating a hard write barrier (e.g. a cache flush that waits) with most if not all ide disks - putting them into powersave should work, if nothing else ;) So apart from driver issues (such as TCQ), the mid-layer needs to be improved (and plans already exist) to support semi-ordered writes and give as much control over the device cache as possible. Not to mention that the VM needs improvements here as well. I didn't say much more than Alan implied: we have to live with it, so we better think about making it work. -- -----==- | ----==-- _ | ---==---(_)__ __ ____ __ Marc Lehmann +-- --==---/ / _ \/ // /\ \/ / pcg@goof.com |e| -=====/_/_//_/\_,_/ /_/\_\ XX11-RIPE --+ The choice of a GNU generation | |