From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [RFC] relaxed barrier semantics Date: Wed, 28 Jul 2010 09:37:19 -0500 Message-ID: <1280327839.30808.188.camel@mulgrave.site> References: <20100727165627.GA474@lst.de> <20100727175418.GF6820@quack.suse.cz> <20100727183546.GG7347@redhat.com> <4C4FE58C.8080403@kernel.org> <4C4FE860.7000903@suse.de> <4C5036BC.30709@vlnb.net> <4C503D50.4010006@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Vladislav Bolkhovitin , Vivek Goyal , Jan Kara , Christoph Hellwig , jaxboe@fusionio.com, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, tytso@mit.edu, chris.mason@oracle.com, swhiteho@redhat.com, konishi.ryusuke@lab.ntt.co.jp To: Tejun Heo Return-path: Received: from cantor.suse.de ([195.135.220.2]:54924 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754869Ab0G1Oh0 (ORCPT ); Wed, 28 Jul 2010 10:37:26 -0400 In-Reply-To: <4C503D50.4010006@suse.de> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, 2010-07-28 at 16:23 +0200, Tejun Heo wrote: > Hello, > > On 07/28/2010 03:55 PM, Vladislav Bolkhovitin wrote: > >> The only benefit of doing it in the block layer, and probably the > >> reason why it was done this way at all, is making use of advanced > >> ordering features of some devices - ordered tag and linked commands. > >> The latter is deprecated and the former is fundamentally broken in > >> error handling anyway. > > > > Why? SCSI provides ACA and UA_INTLCK which provide all needed > > facilities for errors handling in deep ordered queues. > > I don't remember all the details now but IIRC what was necessary was > earlier write failure failing all commands scheduled as ordered. Does > ACA / UA_INTLCK or whatever allow that? No. That requires support for QErr ... which is in the same mode page. The real reason we have difficulty is that BUSY/QUEUE_FULL can cause reordering in the issue queue, which is a driver problem and not in the SCSI standards. James