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SubjectRe: [PATCH 5/6 v4] cfq-iosched: CFQ group hierarchical scheduling and use_hierarchy interface
Vivek Goyal wrote:
> On Thu, Feb 10, 2011 at 03:47:45PM +0800, Gui Jianfeng wrote:
>> CFQ group hierarchical scheduling and use_hierarchy interface.
>>
>
> Hi Gui,
>
> I have done a quick high level review. Some minor comments inline.
>
> [..]
>> struct cfq_data {
>> struct request_queue *queue;
>> - /* Root service tree for cfq_groups */
>> - struct cfq_rb_root grp_service_tree;
>> struct cfq_group root_group;
>>
>> + /* cfq group schedule in flat or hierarchy manner. */
>> + bool use_hierarchy;
>> +
>
> This seems to be redundant now? Nobody is using it?
>
>> /*
>> * The priority currently being served
>> */
>> @@ -246,6 +251,9 @@ struct cfq_data {
>> unsigned long workload_expires;
>> struct cfq_group *serving_group;
>>
>> + /* Service tree for cfq group flat scheduling mode. */
>> + struct cfq_rb_root grp_service_tree;
>
> Above comment is misleading. This service tree is now used both for
> flat as well as hierarhical mode.
>
> [..]
>> static void
>> cfq_group_service_tree_add(struct cfq_data *cfqd, struct cfq_group *cfqg)
>> {
>> - struct cfq_rb_root *st = &cfqd->grp_service_tree;
>> struct cfq_entity *cfqe = &cfqg->cfqe;
>> - struct cfq_entity *__cfqe;
>> struct rb_node *n;
>> + struct cfq_entity *entity;
>> + struct cfq_rb_root *st;
>> + struct cfq_group *__cfqg;
>>
>> cfqg->nr_cfqq++;
>> +
>> if (!RB_EMPTY_NODE(&cfqe->rb_node))
>> 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 continously backlogged.
>> + * Enqueue this group and its ancestors onto their service tree.
>> */
>> - n = rb_last(&st->rb);
>> - if (n) {
>> - __cfqe = rb_entry_entity(n);
>> - cfqe->vdisktime = __cfqe->vdisktime + CFQ_IDLE_DELAY;
>> - } else
>> - cfqe->vdisktime = st->min_vdisktime;
>> + while (cfqe) {
>> + if (!RB_EMPTY_NODE(&cfqe->rb_node))
>> + return;
>>
>> - cfq_entity_service_tree_add(st, cfqe);
>> + /*
>> + * 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 continously backlogged.
>> + */
>
> Can we use vdisktime boost logic for groups also? I think it can be a separate
> patch in the series (the last one). Keeping it as a separate patch will
> also help you to coordinate with chad's patch.
>
>> + st = cfqe->service_tree;
>
> Group entity set their service tree when they get allocated and retain
> this pointer even when they get deleted from serivce tree. Queue entities
> seem to have it NULL when they get deleted from service tree and it
> gets set again when queue is getting inserted. It would be nice if we
> can fix this discrepancy and keep it consistent. I think clearing up
> cfqe->service_tree is a better idea and then calculate it again for
> group also.

Vivek,

Currently, cfq queue might change workload type and io class, so we need to recalculate
its service_tree. But for cfq groups, IMHO we don't need to add this complexity for the
time being.
I think we can add this change as soon as different io classes or workload types are
introduced. How do you think?

Thanks,
Gui


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