From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [GIT PATCH] block: unify request processing model and implement peek/fetch Date: Mon, 11 May 2009 09:52:53 +0200 Message-ID: <20090511075253.GH4694@kernel.dk> References: <1241751256-17435-1-git-send-email-tj@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from brick.kernel.dk ([93.163.65.50]:51246 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753506AbZEKHwx (ORCPT ); Mon, 11 May 2009 03:52:53 -0400 Content-Disposition: inline In-Reply-To: <1241751256-17435-1-git-send-email-tj@kernel.org> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Tejun Heo Cc: linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org, rusty@rustcorp.com.au, James.Bottomley@HansenPartnership.com, mike.miller@hp.com, donari75@gmail.com, paul.clements@steeleye.com, tim@cyberelk.net, Geert.Uytterhoeven@sonycom.com, davem@davemloft.net, Laurent@lvivier.info, jgarzik@pobox.com, jeremy@xensource.com, grant.likely@secretlab.ca, adrian@mcmen.demon.co.uk, sfr@canb.auug.org.au, bzolnier@gmail.com, petkovbb@googlemail.com, sshtylyov@ru.mvista.com, oakad@yahoo.com, drzeus@drzeus.cx, dwmw2@infradead.org, Markus.Lidel@shadowconnect.com, wein@de.ibm.com, schwidefsky@de.ibm.com, zaitcev@redhat.com, fujita.tomonori@lab.ntt.co.jp On Fri, May 08 2009, Tejun Heo wrote: > Hello, > > Upon ack, please pull from the following git tree. > > git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git block-peek-fetch > > Block layer has allowed two different models of request processing. > elv_next_request() is used to peek at the top of the queue, after > peeking, a LLD could start processing it immediately or dequeue and > then start processing. > > The non-dequeuing behavior is mostly useful for simpler device drivers > (usually PIO based) which process requests on segment basis. By using > the block layer queue tip as the current request pointer, they don't > have to care about request boundaries and just process things > segment-by-segment. > > However, this dual mode of operations complicates and ambiguates block > layer API. Block layer can't tell whether a request has begun > processing or not in deterministic manner. This makes accounting > inaccurate and implementing high level features in block layer > difficult. For example, it isn't clear when a block layer timeout > timer should be started or how queue queiscing for EH should be > implemented. Even when problems can be worked aroudn, it makes the > implementation fragile. > > Although allowing llds ignore request boundaries makes things simpler > for certain drivers, the number of drivers benefit form it aren't too > many and driver stacks which are even mildly complex have to deal with > request boundaries anyway. Also, the benefit itself isn't that > significant. In most cases, it is just another way of doing things > rather than the definitively better way. IOW, if there were no such > alternative, nobody would have missed it. > > This patchset converts all block layer llds to dequeuing model and > then clean up API to simplify a bit and enforce dequeueing model. > This patchset contains the following patches. Glad this finally got completed, thanks a lot Tejun! Applied. -- Jens Axboe