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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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