Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751455AbZL1J2s (ORCPT ); Mon, 28 Dec 2009 04:28:48 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750858AbZL1J2r (ORCPT ); Mon, 28 Dec 2009 04:28:47 -0500 Received: from mga01.intel.com ([192.55.52.88]:8329 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750761AbZL1J2r (ORCPT ); Mon, 28 Dec 2009 04:28:47 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.47,459,1257148800"; d="scan'208";a="526686814" Date: Mon, 28 Dec 2009 17:28:44 +0800 From: Shaohua Li To: Corrado Zoccolo Cc: "linux-kernel@vger.kernel.org" , "jens.axboe@oracle.com" , "jmoyer@redhat.com" , "Zhang, Yanmin" Subject: Re: [PATCH]cfq-iosched: don't take requests with long distence as close Message-ID: <20091228092844.GA9710@sli10-desk.sh.intel.com> References: <20091224005506.GA7879@sli10-desk.sh.intel.com> <4e5e476b0912250216n2b4aceacyf22a0e73425efd3a@mail.gmail.com> <20091228020348.GB28115@sli10-desk.sh.intel.com> <4e5e476b0912280036r6e55587dj66952fcd6ff4d08b@mail.gmail.com> <20091228084659.GA31389@sli10-desk.sh.intel.com> <4e5e476b0912280111s6a977251m3416341b4bd2c272@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4e5e476b0912280111s6a977251m3416341b4bd2c272@mail.gmail.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5482 Lines: 125 On Mon, Dec 28, 2009 at 05:11:25PM +0800, Corrado Zoccolo wrote: > Hi Shaohua, > On Mon, Dec 28, 2009 at 9:46 AM, Shaohua Li wrote: > > On Mon, Dec 28, 2009 at 04:36:39PM +0800, Corrado Zoccolo wrote: > >> Hi Shaohua, > >> On Mon, Dec 28, 2009 at 3:03 AM, Shaohua Li wrote: > >> > On Fri, Dec 25, 2009 at 06:16:27PM +0800, Corrado Zoccolo wrote: > >> >> Hi Shaohua, > >> >> On Thu, Dec 24, 2009 at 1:55 AM, Shaohua Li wrote: > >> >> > df5fe3e8e13883f58dc97489076bbcc150789a21 > >> >> > b3b6d0408c953524f979468562e7e210d8634150 > >> >> > The coop merge is too aggressive. For example, if two tasks are reading two > >> >> > files where the two files have some adjecent blocks, cfq will immediately > >> >> > merge them. cfq_rq_close() also has trouble, sometimes the seek_mean is very > >> >> > big. I did a test to make cfq_rq_close() always checks the distence according > >> >> > to CIC_SEEK_THR, but still saw a lot of wrong merge. (BTW, why we take a long > >> >> > distence far away request as close. Taking them close doesn't improve any thoughtput > >> >> > to me. Maybe we should always use CIC_SEEK_THR as close criteria). > >> >> Yes, when deciding if two queues are going to be merged, we should use > >> >> the constant CIC_SEEK_THR. > >> > > >> > seek_mean could be very big sometimes, using it as close criteria is meanless > >> > as this doen't improve any performance. So if it's big, let's fallback to > >> > default value. > >> > >> meanless -> meaningless (also in the comment within code) > > oops > > > >> > Signed-off-by: Shaohua Li > >> > > >> > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > >> > index e2f8046..8025605 100644 > >> > --- a/block/cfq-iosched.c > >> > +++ b/block/cfq-iosched.c > >> > @@ -1682,6 +1682,10 @@ static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq, > >> > ? ? ? ?if (!sample_valid(cfqq->seek_samples)) > >> > ? ? ? ? ? ? ? ?sdist = CFQQ_SEEK_THR; > >> > > >> > + ? ? ? /* if seek_mean is big, using it as close criteria is meanless */ > >> > + ? ? ? if (sdist > CFQQ_SEEK_THR) > >> > + ? ? ? ? ? ? ? sdist = CFQQ_SEEK_THR; > >> > + > >> > ? ? ? ?return cfq_dist_from_last(cfqd, rq) <= sdist; > >> > ?} > >> > > >> > > >> This changes also the cfq_should_preempt behaviour, where a large > >> seek_mean could be meaningful, so I think it is better to add a > >> boolean parameter to cfq_rq_close, to distinguish whether we are > >> preempting or looking for queue merges, and make the new code > >> conditional on merging. > > can you explain why it's meaningful for cfq_should_preempt()? Unless sdist is > > very big, for example > 10*seek_mean, the preempt seems not meaningless. > > Disk access time is a complex function, but for rotational disks it is > 'sort of' increasing with the amplitude of the seek. So, if you have a > new request that is within the mean seek distance (even if it is > larger than our constant), it is good to chose this request instead of > waiting for an other one from the active queue (this behaviour is the > same exhibited by AS, so we need a good reason to change). I have no good reason, but just thought it's a little strange. If other ioscheds take the same way, let's stick. seek_mean could be very big sometimes, using it as close criteria is meaningless as this doen't improve any performance. So if it's big, let's fallback to default value. Signed-off-by: Shaohua Li diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index e2f8046..e80bd47 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1675,13 +1675,17 @@ static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd, #define CFQQ_SEEKY(cfqq) ((cfqq)->seek_mean > CFQQ_SEEK_THR) static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq, - struct request *rq) + struct request *rq, bool for_preempt) { sector_t sdist = cfqq->seek_mean; if (!sample_valid(cfqq->seek_samples)) sdist = CFQQ_SEEK_THR; + /* if seek_mean is big, using it as close criteria is meaningless */ + if (sdist > CFQQ_SEEK_THR && !for_preempt) + sdist = CFQQ_SEEK_THR; + return cfq_dist_from_last(cfqd, rq) <= sdist; } @@ -1709,7 +1713,7 @@ static struct cfq_queue *cfqq_close(struct cfq_data *cfqd, * will contain the closest sector. */ __cfqq = rb_entry(parent, struct cfq_queue, p_node); - if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq)) + if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq, false)) return __cfqq; if (blk_rq_pos(__cfqq->next_rq) < sector) @@ -1720,7 +1724,7 @@ static struct cfq_queue *cfqq_close(struct cfq_data *cfqd, return NULL; __cfqq = rb_entry(node, struct cfq_queue, p_node); - if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq)) + if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq, false)) return __cfqq; return NULL; @@ -3143,7 +3147,7 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq, * if this request is as-good as one we would expect from the * current cfqq, let it preempt */ - if (cfq_rq_close(cfqd, cfqq, rq)) + if (cfq_rq_close(cfqd, cfqq, rq, true)) return true; return false; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/