From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S265962AbTGHCIP (ORCPT ); Mon, 7 Jul 2003 22:08:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266233AbTGHCIO (ORCPT ); Mon, 7 Jul 2003 22:08:14 -0400 Received: from pizda.ninka.net ([216.101.162.242]:6039 "EHLO pizda.ninka.net") by vger.kernel.org with ESMTP id S265962AbTGHCIO (ORCPT ); Mon, 7 Jul 2003 22:08:14 -0400 Date: Mon, 07 Jul 2003 19:14:38 -0700 (PDT) Message-Id: <20030707.191438.71104854.davem@redhat.com> To: ak@suse.de Cc: alan@lxorguk.ukuu.org.uk, grundler@parisc-linux.org, James.Bottomley@SteelEye.com, axboe@suse.de, suparna@in.ibm.com, linux-kernel@vger.kernel.org, alex_williamson@hp.com, bjorn_helgaas@hp.com Subject: Re: [RFC] block layer support for DMA IOMMU bypass mode II From: "David S. Miller" In-Reply-To: <20030703212415.GA30277@wotan.suse.de> References: <20030702235619.GA21567@wotan.suse.de> <1057263988.21508.18.camel@dhcp22.swansea.linux.org.uk> <20030703212415.GA30277@wotan.suse.de> X-FalunGong: Information control. X-Mailer: Mew version 2.1 on Emacs 21.1 / Mule 5.0 (SAKAKI) 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 From: Andi Kleen Date: Thu, 3 Jul 2003 23:24:15 +0200 But of course it doesn't help much in practice because all the interesting block devices support DAC anyways and the IOMMU is disabled for that. Platform dependant. SAC DMA transfers are faster on sparc64 so we only allow the device to specify a 32-bit DMA mask successfully. And actually, I would recommend other platforms that have a IOMMU do this too (unless there is some other reason not to) since virtual merging causes less scatter-gather entries to be used in the device and thus you can stuff more requests into it.