Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264197AbTGBRXM (ORCPT ); Wed, 2 Jul 2003 13:23:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264201AbTGBRXL (ORCPT ); Wed, 2 Jul 2003 13:23:11 -0400 Received: from dsl2.external.hp.com ([192.25.206.7]:53765 "EHLO dsl2.external.hp.com") by vger.kernel.org with ESMTP id S264197AbTGBRXI (ORCPT ); Wed, 2 Jul 2003 13:23:08 -0400 Date: Wed, 2 Jul 2003 11:37:33 -0600 From: Grant Grundler To: Andi Kleen Cc: Grant Grundler , James Bottomley , axboe@suse.de, davem@redhat.com, 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 Message-ID: <20030702173733.GE11739@dsl2.external.hp.com> References: <1057077975.2135.54.camel@mulgrave> <20030702015701.6007ac26.ak@suse.de> <20030702165510.GC11739@dsl2.external.hp.com> <20030702172026.GB32261@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20030702172026.GB32261@wotan.suse.de> User-Agent: Mutt/1.3.28i X-Home-Page: http://www.parisc-linux.org/ Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 952 Lines: 25 On Wed, Jul 02, 2003 at 07:20:26PM +0200, Andi Kleen wrote: ... > > 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. > > Yes, it could. But is that situation likely/worth to handle? Probably. It would reduce the number of mappings by 25% (3 instead of 4). My assumption is two adjecent IOMMU entries have contigious bus addresses. I was trying to figure out if x86-64 should be setting BIO_VMERGE_BOUNDARY to 0 or 4k. It sounds like x86-64 could support "#define BIO_VMERGE_BOUNDARY 4096" if the IOMMU code will return one DMA address for two SG list entries in the above example. hth, grant - 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/