Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760605AbYHHU0W (ORCPT ); Fri, 8 Aug 2008 16:26:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760171AbYHHU0F (ORCPT ); Fri, 8 Aug 2008 16:26:05 -0400 Received: from smtp-out.google.com ([216.239.33.17]:4365 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759945AbYHHU0E (ORCPT ); Fri, 8 Aug 2008 16:26:04 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=message-id:date:from:to:subject:cc:in-reply-to: mime-version:content-type:content-transfer-encoding: content-disposition:references; b=brH8PYfsypUlQ7murspS2DJ4ocPKhxiwlNlJEC5fUIqniAZchpdjUCCgP2LFgMkUZ FcGH2PqoiOWu0Kc9uLucw== Message-ID: Date: Fri, 8 Aug 2008 13:25:59 -0700 From: "Grant Grundler" To: "Stefan Richter" Subject: Re: Scatter-gather segment merges by IOMMU? Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <489CA21F.1030604@s5r6.in-berlin.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <489CA21F.1030604@s5r6.in-berlin.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1292 Lines: 33 On Fri, Aug 8, 2008 at 12:44 PM, Stefan Richter wrote: > Hi all, > > the block layer usually tries to merge s/g segments if consecutive segments > combined fit into the queue's max_segment_size. When such a scatter gather > list is DMA-mapped, can it happen that an IOMMU collapses the elements even > further, so that sg_dma_len() of a DMA-mapped s/g segment exceeds > max_segment_size? I don't see how. The IOMMU code only collapses the "physical" mappings and does not add new elements to the SG list. ergo sg_dma_len() shouldn't change. grant > > As I understood some discussions in the past, this could indeed happen, > which is a nuisance. But I may have misunderstood something, or something > may have changed in the meantime... > -- > Stefan Richter > -=====-==--- =--- -=--- > http://arcgraph.de/sr/ > -- > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- 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/