From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [PATCH 02/18] io-controller: Common flat fair queuing code in elevaotor layer Date: Sat, 23 May 2009 22:04:25 +0200 Message-ID: <20090523200425.GY11363@kernel.dk> References: <1241553525-28095-1-git-send-email-vgoyal@redhat.com> <1241553525-28095-3-git-send-email-vgoyal@redhat.com> <4A164978.1020604@cn.fujitsu.com> <20090522123231.GA14972@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20090522123231.GA14972@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Vivek Goyal Cc: Gui Jianfeng , nauman@google.com, dpshah@google.com, lizf@cn.fujitsu.com, mikew@google.com, fchecconi@gmail.com, paolo.valente@unimore.it, ryov@valinux.co.jp, fernando@oss.ntt.co.jp, s-uchida@ap.jp.nec.com, taka@valinux.co.jp, jmoyer@redhat.com, dhaval@linux.vnet.ibm.com, balbir@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org, righi.andrea@gmail.com, agk@redhat.com, dm-devel@redhat.com, snitzer@redhat.com, m-ikeda@ds.jp.nec.com, akpm@linux-foundation.org List-Id: dm-devel.ids On Fri, May 22 2009, Vivek Goyal wrote: > On Fri, May 22, 2009 at 02:43:04PM +0800, Gui Jianfeng wrote: > > Vivek Goyal wrote: > > ... > > > +/* A request got completed from io_queue. Do the accounting. */ > > > +void elv_ioq_completed_request(struct request_queue *q, struct request *rq) > > > +{ > > > + const int sync = rq_is_sync(rq); > > > + struct io_queue *ioq = rq->ioq; > > > + struct elv_fq_data *efqd = &q->elevator->efqd; > > > + > > > + if (!elv_iosched_fair_queuing_enabled(q->elevator)) > > > + return; > > > + > > > + elv_log_ioq(efqd, ioq, "complete"); > > > + > > > + elv_update_hw_tag(efqd); > > > + > > > + WARN_ON(!efqd->rq_in_driver); > > > + WARN_ON(!ioq->dispatched); > > > + efqd->rq_in_driver--; > > > + ioq->dispatched--; > > > + > > > + if (sync) > > > + ioq->last_end_request = jiffies; > > > + > > > + /* > > > + * If this is the active queue, check if it needs to be expired, > > > + * or if we want to idle in case it has no pending requests. > > > + */ > > > + > > > + if (elv_active_ioq(q->elevator) == ioq) { > > > + if (elv_ioq_slice_new(ioq)) { > > > + elv_ioq_set_prio_slice(q, ioq); > > > > Hi Vivek, > > > > Would you explain a bit why slice_end should be set when first request completes. > > Why not set it just when an ioq gets active? > > > > Hi Gui, > > I have kept the behavior same as CFQ. I guess reason behind this is that > when a new queue is scheduled in, first request completion might take more > time as head of the disk might be quite a distance away (due to previous > queue) and one probably does not want to charge the new queue for that > first seek time. That's the reason we start the queue slice when first > request has completed. That's exactly why CFQ does it that way. And not just for the seek itself, but if have eg writes issued before the switch to a new queue, it's not fair to charge the potential cache writeout happening ahead of the read to that new queue. So I'd definitely recommend keeping this behaviour, as you have. -- Jens Axboe