From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752241AbWFXOcc (ORCPT ); Sat, 24 Jun 2006 10:32:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752249AbWFXOcc (ORCPT ); Sat, 24 Jun 2006 10:32:32 -0400 Received: from smtp.ustc.edu.cn ([202.38.64.16]:59282 "HELO ustc.edu.cn") by vger.kernel.org with SMTP id S1752246AbWFXOcb (ORCPT ); Sat, 24 Jun 2006 10:32:31 -0400 Message-ID: <351159548.15683@ustc.edu.cn> X-EYOUMAIL-SMTPAUTH: wfg@mail.ustc.edu.cn Date: Sun, 25 Jun 2006 14:32:32 +0800 From: Fengguang Wu To: Jens Axboe Cc: linux-kernel@vger.kernel.org, Andrew Morton , Nick Piggin , Lubos Lunak Subject: Re: [PATCH 7/7] iosched: introduce deadline_kick_page() Message-ID: <20060625063232.GA5867@mail.ustc.edu.cn> Mail-Followup-To: Fengguang Wu , Jens Axboe , linux-kernel@vger.kernel.org, Andrew Morton , Nick Piggin , Lubos Lunak References: <20060624082006.574472632@localhost.localdomain> <20060624082312.833976992@localhost.localdomain> <20060624110104.GP4083@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060624110104.GP4083@suse.de> User-Agent: Mutt/1.5.11+cvs20060403 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jun 24, 2006 at 01:01:04PM +0200, Jens Axboe wrote: > > /* > > + * We have a pending read on @page, > > + * find the corresponding request of type READA, > > + * promote it to READ, and reschedule it. > > + */ > > +static int > > +deadline_kick_page(struct request_queue *q, struct page *page) > > +{ > > + struct deadline_data *dd = q->elevator->elevator_data; > > + struct deadline_rq *drq; > > + struct request *rq; > > + struct list_head *pos; > > + struct bio_vec *bvec; > > + struct bio *bio; > > + int i; > > + > > + list_for_each(pos, &dd->fifo_list[READ]) { > > + drq = list_entry_fifo(pos); > > + rq = drq->request; > > + if (rq->flags & (1 << BIO_RW_AHEAD)) { > > + rq_for_each_bio(bio, rq) { > > + bio_for_each_segment(bvec, bio, i) { > > + if (page == bvec->bv_page) > > + goto found; > > + } > > + } > > + } > > + } > > Uh that's horrible! > > Before we go into further details, I'd like to see some numbers on where > this makes a difference. Sorry, it is. It brings non-trivial overhead. This is the oprofile outputs: reading small files: 1245 c01edae4 9 0.1404 deadline_dispatch_requests 1253 c01ed4d6 9 0.1404 deadline_queue_empty 1338 c01ed3d5 8 0.1248 deadline_kick_page 1619 c01ed350 6 0.0936 deadline_add_drq_fifo 1707 c01eda62 5 0.0780 deadline_add_request 1712 c01ed2e5 5 0.0780 deadline_set_request 1867 c01ed871 4 0.0624 deadline_remove_request 2242 c01ed9b9 2 0.0312 deadline_add_drq_rb 2244 c01edc1e 2 0.0312 deadline_merge 2246 c01ed923 2 0.0312 deadline_move_request 2249 c01ed232 2 0.0312 deadline_put_request reading a big file: 1330 c01ed3d5 89 0.2926 deadline_kick_page 2528 c01edae4 16 0.0526 deadline_dispatch_requests 3036 c01ed9b9 8 0.0263 deadline_add_drq_rb 3163 c01ed4d6 7 0.0230 deadline_queue_empty 3394 c01edc1e 5 0.0164 deadline_merge 3399 c01ed923 5 0.0164 deadline_move_request 3403 c01ed2e5 5 0.0164 deadline_set_request 3707 c01eda62 3 0.0099 deadline_add_request 3711 c01ed871 3 0.0099 deadline_remove_request 3917 c01ede3c 2 0.0066 deadline_merged_request 3920 c01ed232 2 0.0066 deadline_put_request 4214 c01ed350 1 0.0033 deadline_add_drq_fifo The overhead of deadline_kick_page() becomes large when the request is large (256 pages). But I guess there's way to optimize it: - most requests will be consisted of a set of continuous pages, i.e. a range comparison will be sufficient. - for a system with lots of queued requests(>100), maybe the gain can well pay for the overheads? btw, some mails for this patchset did not return to me, perhaps my mail system was broken after a previous crash... Sorry, I'll resend them soon. Thanks, Wu