From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934057AbXC0F7Y (ORCPT ); Tue, 27 Mar 2007 01:59:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S934058AbXC0F7Y (ORCPT ); Tue, 27 Mar 2007 01:59:24 -0400 Received: from srv5.dvmed.net ([207.36.208.214]:33172 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934057AbXC0F7X (ORCPT ); Tue, 27 Mar 2007 01:59:23 -0400 Message-ID: <4608B2B9.7090503@garzik.org> Date: Tue, 27 Mar 2007 01:59:21 -0400 From: Jeff Garzik User-Agent: Thunderbird 1.5.0.10 (X11/20070302) MIME-Version: 1.0 To: Justin Piszcz CC: linux-kernel@vger.kernel.org, IDE/ATA development list Subject: Re: Why is NCQ enabled by default by libata? (2.6.20) References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Score: -4.3 (----) X-Spam-Report: SpamAssassin version 3.1.8 on srv5.dvmed.net summary: Content analysis details: (-4.3 points, 5.0 required) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Justin Piszcz wrote: > Without NCQ, performance is MUCH better on almost every operation, with > the exception of 2-3 items. Variables to take into account: * the drive (NCQ performance wildly varies) * the IO scheduler * the filesystem (if not measuring direct to blkdev) * application workload (or in your case, benchmark tool) * in particular, the threaded-ness of the apps For the overwhelming majority of combinations, NCQ should not /hurt/ performance. For the majority of combinations, NCQ helps (though it may not be often that you use more than 4-8 tags). In some cases, NCQ firmware may be broken. There is a Maxtor firmware id, and some Hitachi ids that people are leaning towards recommending be added to the libata 'horkage' list. Jeff