Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966687Ab0GSUUg (ORCPT ); Mon, 19 Jul 2010 16:20:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38046 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966644Ab0GSUUf (ORCPT ); Mon, 19 Jul 2010 16:20:35 -0400 Date: Mon, 19 Jul 2010 16:20:24 -0400 From: Vivek Goyal To: Jeff Moyer Cc: linux-kernel@vger.kernel.org, axboe@kernel.dk, nauman@google.com, dpshah@google.com, guijianfeng@cn.fujitsu.com, czoccolo@gmail.com Subject: Re: [PATCH 2/3] cfq-iosched: Implement a new tunable group_idle Message-ID: <20100719202024.GD32503@redhat.com> References: <1279560008-2905-1-git-send-email-vgoyal@redhat.com> <1279560008-2905-3-git-send-email-vgoyal@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-12-10) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5259 Lines: 148 On Mon, Jul 19, 2010 at 02:58:41PM -0400, Jeff Moyer wrote: > Vivek Goyal writes: > > > o Implement a new tunable group_idle, which allows idling on the group > > instead of a cfq queue. Hence one can set slice_idle = 0 and not idle > > on the individual queues but idle on the group. This way on fast storage > > we can get fairness between groups at the same time overall throughput > > improves. > > > > Signed-off-by: Vivek Goyal > > --- > > block/cfq-iosched.c | 60 +++++++++++++++++++++++++++++++++++++++++++++------ > > 1 files changed, 53 insertions(+), 7 deletions(-) > > > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > > index f44064c..b23d7f4 100644 > > --- a/block/cfq-iosched.c > > +++ b/block/cfq-iosched.c > > @@ -30,6 +30,7 @@ static const int cfq_slice_sync = HZ / 10; > > static int cfq_slice_async = HZ / 25; > > static const int cfq_slice_async_rq = 2; > > static int cfq_slice_idle = HZ / 125; > > +static int cfq_group_idle = HZ / 125; > > static const int cfq_target_latency = HZ * 3/10; /* 300 ms */ > > static const int cfq_hist_divisor = 4; > > > > @@ -198,6 +199,8 @@ struct cfq_group { > > struct hlist_node cfqd_node; > > atomic_t ref; > > #endif > > + /* number of requests that are on the dispatch list or inside driver */ > > + int dispatched; > > }; > > > > /* > > @@ -271,6 +274,7 @@ struct cfq_data { > > unsigned int cfq_slice[2]; > > unsigned int cfq_slice_async_rq; > > unsigned int cfq_slice_idle; > > + unsigned int cfq_group_idle; > > unsigned int cfq_latency; > > unsigned int cfq_group_isolation; > > > > @@ -1856,6 +1860,9 @@ static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq) > > BUG_ON(!service_tree); > > BUG_ON(!service_tree->count); > > > > + if (!cfqd->cfq_slice_idle) > > + return false; > > + > > /* We never do for idle class queues. */ > > if (prio == IDLE_WORKLOAD) > > return false; > > @@ -1880,7 +1887,7 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd) > > { > > struct cfq_queue *cfqq = cfqd->active_queue; > > struct cfq_io_context *cic; > > - unsigned long sl; > > + unsigned long sl, group_idle = 0; > > > > /* > > * SSD device without seek penalty, disable idling. But only do so > > @@ -1896,8 +1903,13 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd) > > /* > > * idle is disabled, either manually or by past process history > > */ > > - if (!cfqd->cfq_slice_idle || !cfq_should_idle(cfqd, cfqq)) > > - return; > > + if (!cfqd->cfq_slice_idle || !cfq_should_idle(cfqd, cfqq)) { > > The check for cfqd->cfq_slice_idle is now redundant (as it's done in > cfq_should_idle). Yep. I will get rid of extra check. > > > @@ -2215,7 +2236,7 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd) > > cfqq = NULL; > > goto keep_queue; > > } else > > - goto expire; > > + goto check_group_idle; > > } > > > > /* > > @@ -2249,6 +2270,17 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd) > > goto keep_queue; > > } > > > > + /* > > + * If group idle is enabled and there are requests dispatched from > > + * this group, wait for requests to complete. > > + */ > > +check_group_idle: > > + if (cfqd->cfq_group_idle && cfqq->cfqg->nr_cfqq == 1 > > + && cfqq->cfqg->dispatched) { > > + cfqq = NULL; > > + goto keep_queue; > > + } > > I really wish we could roll all of this logic into cfq_should_idle. Currently whether to idle on queue or not logic is also part of select_queue(). So to keep it same it makes sense to keep group logic also in select_queue(). > > > @@ -3420,7 +3453,10 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq) > > * the queue. > > */ > > if (cfq_should_wait_busy(cfqd, cfqq)) { > > - cfqq->slice_end = jiffies + cfqd->cfq_slice_idle; > > + unsigned long extend_sl = cfqd->cfq_slice_idle; > > + if (!cfqd->cfq_slice_idle) > > + extend_sl = cfqd->cfq_group_idle; > > + cfqq->slice_end = jiffies + extend_sl; > > So, if slice_idle and group_idle are both set, slice_idle trumps > group_idle? Did you give that case any thought? If it doesn't make > sense to configure both, then we should probably make sure they can't > both be set. Actually, the wait busy logic makes sense in case of slice_idle, where we can give an extended slice to a queue and to make sure a queue/group does not get deleted immediately after completing the slice and hence losing the share. Now in case of slice_idle=0, if there is only one queue in the group then it becomes the same case as one queue in the group with slice_idle=8. So yes, slice_idle trumps group_idle. group_idle kicks in only if slice_idle=0. I think by default it being set it does not harm. What good it will do if slice_idle=8 and group_idle=0. Instead it will become more work for user to also set one more tunable if he plans to set slice_idle=0. Thanks Vivek > > Cheers, > Jeff -- 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/