Re: [PATCH 05/16] blkio: Implement per cfq group latency targetand busy queue avg
From: Vivek Goyal
Date: Fri Nov 13 2009 - 10:19:13 EST
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@xxxxxxxxxx> 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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