Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261523AbVE3Gc1 (ORCPT ); Mon, 30 May 2005 02:32:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261528AbVE3Gc1 (ORCPT ); Mon, 30 May 2005 02:32:27 -0400 Received: from brick.kernel.dk ([62.242.22.158]:18409 "EHLO nelson.home.kernel.dk") by vger.kernel.org with ESMTP id S261523AbVE3GcV (ORCPT ); Mon, 30 May 2005 02:32:21 -0400 Date: Mon, 30 May 2005 08:33:23 +0200 From: Jens Axboe To: Greg Stark Cc: "Eric D. Mudama" , Matthias Andree , linux-kernel@vger.kernel.org, jgarzik@pobox.com Subject: Re: [PATCH] SATA NCQ support Message-ID: <20050530063322.GE7054@suse.de> References: <20050527070353.GL1435@suse.de> <20050527131842.GC19161@merlin.emma.line.org> <20050527135258.GW1435@suse.de> <429732CE.5010708@gmx.de> <20050527145821.GX1435@suse.de> <87oeatxtw4.fsf@stark.xeocode.com> <311601c905052921046692cd3e@mail.gmail.com> <87d5r9xmgr.fsf@stark.xeocode.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87d5r9xmgr.fsf@stark.xeocode.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1479 Lines: 36 On Mon, May 30 2005, Greg Stark wrote: > > ATA has a limitation of 32 tags, so queued write cache off won't beat > > unqueued write cache on in any modern drive. > > People earlier were quoting 30-40% gains with NCQ enabled. I assumed > those were with the same drive in otherwise the same configuration, > presumably with write-caching enabled. If you are talking about the numbers I quoted, those were for random read performance. > Without any form of command queueing write-caching imposes a severe > performance loss, the question is how much of that loss is erased when > NCQ is present. I'll try some random write tests with write caching disabled. > People actually tend to report that IDE drives are *faster*. Until > they're told they have to disable write-caching on their IDE drives to > get a fair comparison, then the performance is absolutely abysmal. The > interesting thing is that SCSI drives don't seem to take much of a > performance hit from having write-caching disabled while IDE drives > do. NCQ will surely lessen the impact of disabling write caching, how much still remains to be seen. You could test, if you have the hardware :) Real life testing is more interesting than benchmarks. -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/