From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [RFC] relaxed barrier semantics Date: Wed, 28 Jul 2010 16:44:07 +0200 Message-ID: <4C504237.4070105@suse.de> 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> <1280327839.30808.188.camel@mulgrave.site> 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: James Bottomley Return-path: In-Reply-To: <1280327839.30808.188.camel@mulgrave.site> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Hello, On 07/28/2010 04:37 PM, James Bottomley wrote: >> 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. I see. > 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. Ah yeah right. ISTR discussions about this years ago. But one way or the other, given the limited amount of ordering information available under the block layer, I doubt the benefit of doing would be anything significant. If it can be done w/o too much complexity, sure, but otherwise... Thanks. -- tejun