Messages in this thread | | | Date | Thu, 23 Jun 2011 13:51:18 -0400 | From | Vivek Goyal <> | Subject | Re: [PATCH] cfq-iosched: queue groups more gracefully |
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On Thu, Jun 23, 2011 at 08:22:06PM +0400, Konstantin Khlebnikov wrote: > This patch queue awakened cfq-groups according its current vdisktime, > it try to save upto one group timeslice from unused virtual disk time. > Thus group does not loses everything, if it was not continuously backlogged. > > Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
I think this patch is not required till we start preemption across groups? Any more details of actual use will help.
> --- > block/cfq-iosched.c | 36 ++++++++++++++++++++++++++++++------ > 1 files changed, 30 insertions(+), 6 deletions(-) > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index c71533e..d5c7c79 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -592,6 +592,26 @@ cfq_group_slice(struct cfq_data *cfqd, struct cfq_group *cfqg) > return cfq_target_latency * cfqg->weight / st->total_weight; > } > > +static inline u64 > +cfq_group_vslice(struct cfq_data *cfqd, struct cfq_group *cfqg) > +{ > + struct cfq_rb_root *st = &cfqd->grp_service_tree; > + u64 vslice; > + > + /* There no group slices in iops mode */ > + if (iops_mode(cfqd)) > + return 0; > + > + /* > + * Equal to cfq_scale_slice(cfq_group_slice(cfqd, cfqg), cfqg). > + * Add group weight beacuse it currently not in service tree. > + */ > + vslice = (u64)cfq_target_latency << CFQ_SERVICE_SHIFT; > + vslice *= BLKIO_WEIGHT_DEFAULT; > + do_div(vslice, st->total_weight + cfqg->weight);
Above is not equivalent to cfq_scale_slice(cfq_group_slice(cfqd, cfqg), cfqg) as comment says.
you are not calculating cfq_group_slice(). Instead using cfq_target_latency.
Also it does not make sense. A higher weight group gets lower vslice and in turn gets put further away on the tree. This is reverse of what you want.
> + return vslice; > +} > + > static inline unsigned > cfq_scaled_cfqq_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq) > { > @@ -884,16 +904,20 @@ cfq_group_notify_queue_add(struct cfq_data *cfqd, struct cfq_group *cfqg) > return; > > /* > - * Currently put the group at the end. Later implement something > - * so that groups get lesser vtime based on their weights, so that > - * if group does not loose all if it was not continuously backlogged. > + * Bump vdisktime to be greater or equal min_vdisktime. > + */ > + cfqg->vdisktime = max_vdisktime(cfqg->vdisktime, st->min_vdisktime); > +
why do we need to do this?
> + /* > + * Put the group at the end, but save one slice from unused time. > */ > n = rb_last(&st->rb); > if (n) { > __cfqg = rb_entry_cfqg(n); > - cfqg->vdisktime = __cfqg->vdisktime + CFQ_IDLE_DELAY; > - } else > - cfqg->vdisktime = st->min_vdisktime; > + cfqg->vdisktime = max_vdisktime(cfqg->vdisktime, ^^^^^^^ I think you meant st->min_vdisktime here? > + __cfqg->vdisktime - > + cfq_group_vslice(cfqd, cfqg)); > + } > cfq_group_service_tree_add(st, cfqg); > } >
Thanks Vivek
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