From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: SCSI breakage on non-cache coherent architectures Date: Tue, 20 Nov 2007 06:54:28 +1100 Message-ID: <1195502068.6970.3.camel@pasglop> References: <1195450523.7022.37.camel@pasglop> <20071119123240.GA12494@parisc-linux.org> <1195484964.3283.4.camel@localhost.localdomain> Reply-To: benh@kernel.crashing.org Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from gate.crashing.org ([63.228.1.57]:59791 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751315AbXKSTyl (ORCPT ); Mon, 19 Nov 2007 14:54:41 -0500 In-Reply-To: <1195484964.3283.4.camel@localhost.localdomain> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: Matthew Wilcox , Linux Kernel list , linux-scsi , Russell King On Mon, 2007-11-19 at 09:09 -0600, James Bottomley wrote: > > What other drivers do is DMA to their own allocation and then memcpy to > > the sense buffer. > > > > There is a movement to allocate the sense data as its own sg list, but > > I don't think that patch has even been posted yet. > > I'd like to be rid of it inside the command for various reasons: every > command has one of these, and they're expensive in the allocation (at 96 > bytes). There's no reason we have to allocate and free that amount of > space with every command. In theory, the number of these is bounded at > the queue depth, in practice, there's usually only one, and this DMA > alignment issue does requires most drivers to double copy. And most drivers don't and break. Take USB storage, I -think- (code path aren't trivial to follow) it just gets the sglist cooked up by the code in scsi_error.c no ? That just points to the buffer in scsi_cmnd. It then pass that for DMA to the USB stack. Ben.