From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 15 Nov 2002 19:09:50 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 15 Nov 2002 19:09:49 -0500 Received: from krusty.dt.E-Technik.Uni-Dortmund.DE ([129.217.163.1]:3089 "EHLO mail.dt.e-technik.uni-dortmund.de") by vger.kernel.org with ESMTP id ; Fri, 15 Nov 2002 19:09:49 -0500 Date: Sat, 16 Nov 2002 01:16:41 +0100 From: Matthias Andree To: linux-kernel@vger.kernel.org Subject: Re: IDE TCQ Message-ID: <20021116001641.GD26188@merlin.emma.line.org> Mail-Followup-To: linux-kernel@vger.kernel.org References: <71EE24368CCFB940A79BD7002F14D760409348@exchange.uns.t-systems.tss> <20021113113940.GE832@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20021113113940.GE832@suse.de> User-Agent: Mutt/1.5.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 13 Nov 2002, Jens Axboe wrote: > > Second set of questions: Does it do any good to one-channel-one-disk > > setups? Is it supposed to do good to access time, operations/sec, > > throughput, random reqs rearrangement or what? Do you have any > > figures how much TCQ helps performace (e.g. in file serving case)? > > Yes it will help any setup. Due to way ide tcq works, it's recommended > only to use tcq on one drive on a channel right now. This may change in > the future. Would be "it's recommended to use only one drive on a channel for best results, whether with or without TCQ" more accurate? Or are there reasons that make TCQ <-> slave interactions particularly bad that don't show up without TCQ? > I don't have any general numbers. I did some benchmarking when I first > implemented it, and it typically shows (as with scsi drives) that having > just enough tags to keep the disk busy helps a bit. The linux io > scheduler does the rest. For random reads, 10-30% speed increase was > observed. Did you perchance benchmark the impact TCQ has on sequential writes when the write cache is turned off? Turning off the write cache without TCQ has a severe impact (30 to 70% on my "stupid dd" tests) in my computer (VIA82C686, but I don't recall which drive I did this on, it was either of IBM DJNA, DTLA or Maxtor 4W060H4)