Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264611AbTGBVFa (ORCPT ); Wed, 2 Jul 2003 17:05:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264643AbTGBVFa (ORCPT ); Wed, 2 Jul 2003 17:05:30 -0400 Received: from pc2-cwma1-4-cust86.swan.cable.ntl.com ([213.105.254.86]:34709 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S264611AbTGBVFZ (ORCPT ); Wed, 2 Jul 2003 17:05:25 -0400 Subject: Re: [RFC] block layer support for DMA IOMMU bypass mode II From: Alan Cox To: Grant Grundler Cc: Andi Kleen , James Bottomley , axboe@suse.de, davem@redhat.com, suparna@in.ibm.com, Linux Kernel Mailing List , alex_williamson@hp.com, bjorn_helgaas@hp.com In-Reply-To: <20030702165510.GC11739@dsl2.external.hp.com> References: <1057077975.2135.54.camel@mulgrave> <20030702015701.6007ac26.ak@suse.de> <20030702165510.GC11739@dsl2.external.hp.com> Content-Type: text/plain Content-Transfer-Encoding: 7bit Organization: Message-Id: <1057180598.20318.32.camel@dhcp22.swansea.linux.org.uk> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.2.2 (1.2.2-5) Date: 02 Jul 2003 22:16:39 +0100 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1189 Lines: 24 On Mer, 2003-07-02 at 17:55, Grant Grundler wrote: > On Wed, Jul 02, 2003 at 01:57:01AM +0200, Andi Kleen wrote: > > The K8 IOMMU cannot support this virtually contiguous thing. The reason > > is that there is no guarantee that an entry in a sglist is a multiple > > of page size. And the aperture can only map 4K sized chunks, like > > a CPU MMU. So e.g. when you have an sglist with multiple 1K entries there is > > no way to get them continuous in IOMMU space (short of copying) > > Can two adjacent IOMMU entries be used to map two 1K buffers? > Assume the 1st buffer ends on a 4k alignment and the next one > starts on a 4k alignment. When I played with optimising merging on some 2.4 I2O and aacraid controller stuff I found two things 1. We allocate pages in reverse order so most merges cant occur 2. If you use a 4K fs as most people do now the issue is irrelevant 3. Almost every 1K mergable was part of the same 4K page anyway - 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/