From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: Regarding ordered-tag support. Date: Fri, 10 Feb 2006 09:45:16 +0900 Message-ID: <43EBE21C.2020803@gmail.com> References: <43E99248.7090505@gmail.com> <1139413766.3003.19.camel@mulgrave.il.steeleye.com> <43EA17E6.4000800@gmail.com> <43EA1B75.40008@emulex.com> <43EA2313.9030506@gmail.com> <1139418451.3003.37.camel@mulgrave.il.steeleye.com> <43EA27E4.9080105@gmail.com> <1139419637.3003.43.camel@mulgrave.il.steeleye.com> <43EA329F.2000906@pobox.com> <43EAC110.5030700@gmail.com> <1139505635.3275.43.camel@mulgrave.il.steeleye.com> Mime-Version: 1.0 Content-Type: text/plain; charset=EUC-KR Content-Transfer-Encoding: 7bit Return-path: Received: from pproxy.gmail.com ([64.233.166.176]:12989 "EHLO pproxy.gmail.com") by vger.kernel.org with ESMTP id S1750894AbWBJApV (ORCPT ); Thu, 9 Feb 2006 19:45:21 -0500 Received: by pproxy.gmail.com with SMTP id 57so130388pya for ; Thu, 09 Feb 2006 16:45:20 -0800 (PST) In-Reply-To: <1139505635.3275.43.camel@mulgrave.il.steeleye.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: Jeff Garzik , James.Smart@Emulex.Com, SCSI Mailing List Hello, James. James Bottomley wrote: > > The fact that tasks can proceed in parallel, only the command components > individual linked tasks must be serialised. so it supports the TCQ > paradigm. > > Really, also, linked tasks is exactly what a JFS wants because most of > the updates that would be linked are something like update log entry; > modify metadata (or data); remove log entry. > I see your point, so it's not really a barrier anymore, but a sequence of ordered writes with an intervening flush independent of other unrelated writes. Some random thoughts... * All writes in the ordered sequence will have to be done sequentially, but unrelated writes are not affected. This can be overall gain. * Can be implemented in block layer proper without using SCSI linked task (probably with separate ->ordered_requests queue). What would be the advantage of SCSI linked task? * As it's finer grained than wholesale barrier, FS layer will need to pay more attention. Thanks for the explanation. :-) -- tejun