Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933817Ab0GOQkz (ORCPT ); Thu, 15 Jul 2010 12:40:55 -0400 Received: from 0122700014.0.fullrate.dk ([95.166.99.235]:35366 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933757Ab0GOQky (ORCPT ); Thu, 15 Jul 2010 12:40:54 -0400 Message-ID: <4C3F3A0C.10909@kernel.dk> Date: Thu, 15 Jul 2010 10:40:44 -0600 From: Jens Axboe MIME-Version: 1.0 To: "Martin K. Petersen" CC: Christof Schmitt , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch 0/1] Apply segment size and segment boundary to integrity data References: <20100715153410.774329000@de.ibm.com> <4C3F3400.7060005@kernel.dk> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1595 Lines: 37 On 07/15/2010 10:35 AM, Martin K. Petersen wrote: >>>>>> "Jens" == Jens Axboe writes: > > Jens> That sounds like a very batch design decision. Either the limits > Jens> are explicitly given and different, or if not we have to assume > Jens> that they are the same as the data limits at least. > > Imagine a controller that has a 4KB segment, 1 entry limit. If we > capped the DI sgl the same way as the data we'd only be able to issue > 512-byte requests unless the DI entries happened to be contiguous in > memory. > > For several types of I/O the DI sgl is much longer than the data sgl. > Especially if the submitter is using buffer_heads to map 512-byte > blocks. > > And consequently we require vendors to be able to handle the > pathological case in which any data scatterlist honoring the > segmentation constraints given by the driver can be matched with an > integrity scatterlist in which there is a separate entry for each > logical block. No vendor has had any problems with this. Therefore > there are no block layer data integrity queue limits. > > If a device appears that does in fact have constraints I have no > problems intruducing a set of suitable knobs. OK, lets wait and hear what problem that Christof ran into here. Is it ensuring that a segment doesn't corss eg the 4GB boundary? -- Jens Axboe -- 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/