From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [PATCH] bsg: Add support for submitting requests at tail of queue Date: Thu, 22 Jan 2009 12:13:02 +0100 Message-ID: <20090122111302.GG30821@kernel.dk> References: <4976F067.8000501@panasas.com> <20090122082314G.fujita.tomonori@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from brick.kernel.dk ([93.163.65.50]:1294 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753179AbZAVLOh (ORCPT ); Thu, 22 Jan 2009 06:14:37 -0500 Content-Disposition: inline In-Reply-To: <20090122082314G.fujita.tomonori@lab.ntt.co.jp> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: FUJITA Tomonori Cc: bharrosh@panasas.com, dougg@torque.net, linux-scsi@vger.kernel.org, osd-dev@open-osd.org On Thu, Jan 22 2009, FUJITA Tomonori wrote: > On Wed, 21 Jan 2009 11:52:39 +0200 > Boaz Harrosh wrote: > > > > > Currently inherited from sg.c bsg will submit asynchronous request > > at the head-of-the-queue, (using "at_head" set in the call to > > blk_execute_rq_nowait()). This is bad in situation where we want > > to keep the queues full but need the requests to execute in order. > > As I wrote, I think that blk_execute_rq_nowait inserts a request and > plugs a queue. So how can you keep the queue full? On the completion > of blk_execute_rq_nowait, the queue is empty. That's not true at all. If you submit more than one request, request 2 and up would be queued according to the orientation given. It may even include request 1 as well, what if the queue is busy doing work for someone else already? I think the patch makes sense, I also wish that the default would have been reversed so that at_back would be the default. at_back is more complex though, since it impacts existing requests for the device (it drains the scheduler queue). -- Jens Axboe