Date: Fri, 13 Nov 2009 10:18:15 -0500
From: Vivek Goyal <vgoyal@redhat.com>
To: Corrado Zoccolo <czoccolo@gmail.com>
Cc: linux-kernel@vger.kernel.org, jens.axboe@oracle.com, nauman@google.com,
       dpshah@google.com, lizf@cn.fujitsu.com, ryov@valinux.co.jp,
       fernando@oss.ntt.co.jp, s-uchida@ap.jp.nec.com, taka@valinux.co.jp,
       guijianfeng@cn.fujitsu.com, jmoyer@redhat.com,
       balbir@linux.vnet.ibm.com, righi.andrea@gmail.com,
       m-ikeda@ds.jp.nec.com, akpm@linux-foundation.org, riel@redhat.com,
       kamezawa.hiroyu@jp.fujitsu.com
Subject: Re: [PATCH 05/16] blkio: Implement per cfq group latency target
	and busy queue avg
Message-ID: <20091113151815.GC17076@redhat.com>
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On Fri, Nov 13, 2009 at 11:46:49AM +0100, Corrado Zoccolo wrote:
> On Fri, Nov 13, 2009 at 12:32 AM, Vivek Goyal <vgoyal@redhat.com> wrote:
> > ?static inline void
> > @@ -441,10 +445,13 @@ cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
> > ? ? ? ?if (cfqd->cfq_latency) {
> > ? ? ? ? ? ? ? ?/* interested queues (we consider only the ones with the same
> > ? ? ? ? ? ? ? ? * priority class) */
> This comment needs to be updated

Sure. Will do. Now the interested queues are the one with same priority
class with-in group.

> > ? ? ? ? ? ? ? ? * priority class) */
> > - ? ? ? ? ? ? ? unsigned iq = cfq_get_avg_queues(cfqd, cfq_class_rt(cfqq));
> > + ? ? ? ? ? ? ? unsigned iq = cfq_group_get_avg_queues(cfqd, cfqq->cfqg,
> > + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? cfq_class_rt(cfqq));
> > ? ? ? ? ? ? ? ?unsigned sync_slice = cfqd->cfq_slice[1];
> > ? ? ? ? ? ? ? ?unsigned expect_latency = sync_slice * iq;
> > - ? ? ? ? ? ? ? if (expect_latency > cfq_target_latency) {
> > + ? ? ? ? ? ? ? unsigned group_target_lat = cfq_target_latency/cfqd->nr_groups;
> 
> I'm not sure that we should divide the target latency evenly among groups.
> Groups with different weights will have different percentage of time
> in each 300ms round, so probably we should consider it here.
> 

Taking group weight into account will be more precise thing. So may be
I can keep track of total weight on the service tree and determine
group target latency as proportion of total weight.

 group_target_lat = group_weight * cfq_target_latency/total_weight_of_groups

Thanks
Vivek

> > +
> > + ? ? ? ? ? ? ? if (expect_latency > group_target_lat) {
> > ? ? ? ? ? ? ? ? ? ? ? ?unsigned base_low_slice = 2 * cfqd->cfq_slice_idle;
> > ? ? ? ? ? ? ? ? ? ? ? ?/* scale low_slice according to IO priority
> > ? ? ? ? ? ? ? ? ? ? ? ? * and sync vs async */
> > @@ -452,7 +459,7 @@ cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
> > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?min(slice, base_low_slice * slice / sync_slice);
> > ? ? ? ? ? ? ? ? ? ? ? ?/* the adapted slice value is scaled to fit all iqs
> > ? ? ? ? ? ? ? ? ? ? ? ? * into the target latency */
> > - ? ? ? ? ? ? ? ? ? ? ? slice = max(slice * cfq_target_latency / expect_latency,
> > + ? ? ? ? ? ? ? ? ? ? ? slice = max(slice * group_target_lat / expect_latency,
> > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?low_slice);
> > ? ? ? ? ? ? ? ?}
> > ? ? ? ?}
> 
> Thanks,
> Corrado
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