Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755267AbYFZCGv (ORCPT ); Wed, 25 Jun 2008 22:06:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752335AbYFZCGn (ORCPT ); Wed, 25 Jun 2008 22:06:43 -0400 Received: from sh.osrg.net ([192.16.179.4]:35098 "EHLO sh.osrg.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751832AbYFZCGn (ORCPT ); Wed, 25 Jun 2008 22:06:43 -0400 Date: Thu, 26 Jun 2008 11:06:03 +0900 To: stern@rowland.harvard.edu Cc: fujita.tomonori@lab.ntt.co.jp, andi@firstfloor.org, linux-kernel@vger.kernel.org, antonio.lin@alcormicro.com, david.vrabel@csr.com Subject: Re: Scatter-gather list constraints From: FUJITA Tomonori In-Reply-To: References: <20080625091813Z.fujita.tomonori@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-Id: <20080626110615U.fujita.tomonori@lab.ntt.co.jp> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1791 Lines: 41 On Wed, 25 Jun 2008 10:23:00 -0400 (EDT) Alan Stern wrote: > On Wed, 25 Jun 2008, FUJITA Tomonori wrote: > > > > For example, suppose an I/O request starts out with two S-G elements > > > of 1536 bytes and 2048 bytes respectively, and the DMA requirement is > > > that all elements except the last must have length divisible by 1024. > > > Then the request could be broken up into three requests of 1024, 512, > > > and 2048 bytes. > > > > I can't say that it's easy to implement a clean mechanism to break up > > a request into multiple requests until I see a patch. > > And I can't write a patch without learning a lot more about how the > block core works. > > > What I said is that you think that this is about extending something > > in the block layer but it's about adding a new concept to the block > > layer. > > Is it? What does the block layer do when it receives an I/O request > that don't satisfy the other constraints (max_sectors or > dma_alignment_mask, for example)? As I explained, you need something new. I don't think that max_sectors works as you expect. dma_alignment_mask is not used in the FS path. And I think that dma_alignment_mask doens't solve your problems. > > > Is it reasonable to have 120-KB bounce buffers? > > > > The block layer does. Why do you think that USB can't? > > Why do you think I think that USB can't? I didn't ask whether it was > _possible_; I asked whether it was _reasonable_. What the block layer does is reasonable with regard to this, I think. -- 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/