Re: [PATCH] cfq-iosched: Get rid of st->active

From: Vivek Goyal
Date: Tue Nov 30 2010 - 09:28:59 EST


On Tue, Nov 30, 2010 at 04:37:26PM +0800, Gui Jianfeng wrote:
> When a cfq group is running, it won't be dequeued from service tree, so
> there's no need to store the active one in st->active. Just gid rid of it.
>
> Signed-off-by: Gui Jianfeng <guijianfeng@xxxxxxxxxxxxxx>
> Acked-by: Vivek Goyal <vgoyal@xxxxxxxxxx>

Looks good to me. st->left and st->active seems to be same as we never
dequeue the group while it is being serviced.

I think in previous implementations I had first dequeued the group while
it is being serviced and in that case st->left and st->active will be
different, hence this additional pointer. Later changed the implementation
and now st->active should not be needed.

Thanks for the cleanup Gui.

Acked-by: Vivek Goyal <vgoyal@xxxxxxxxxx>

Vivek

> ---
> block/cfq-iosched.c | 15 +--------------
> 1 files changed, 1 insertions(+), 14 deletions(-)
>
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 73a5862..e18d316 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -87,7 +87,6 @@ struct cfq_rb_root {
> unsigned count;
> unsigned total_weight;
> u64 min_vdisktime;
> - struct rb_node *active;
> };
> #define CFQ_RB_ROOT (struct cfq_rb_root) { .rb = RB_ROOT, .left = NULL, \
> .count = 0, .min_vdisktime = 0, }
> @@ -563,11 +562,6 @@ static void update_min_vdisktime(struct cfq_rb_root *st)
> u64 vdisktime = st->min_vdisktime;
> struct cfq_group *cfqg;
>
> - if (st->active) {
> - cfqg = rb_entry_cfqg(st->active);
> - vdisktime = cfqg->vdisktime;
> - }
> -
> if (st->left) {
> cfqg = rb_entry_cfqg(st->left);
> vdisktime = min_vdisktime(vdisktime, cfqg->vdisktime);
> @@ -894,9 +888,6 @@ cfq_group_service_tree_del(struct cfq_data *cfqd, struct cfq_group *cfqg)
> {
> struct cfq_rb_root *st = &cfqd->grp_service_tree;
>
> - if (st->active == &cfqg->rb_node)
> - st->active = NULL;
> -
> BUG_ON(cfqg->nr_cfqq < 1);
> cfqg->nr_cfqq--;
>
> @@ -1095,7 +1086,7 @@ static void cfq_put_cfqg(struct cfq_group *cfqg)
> if (!atomic_dec_and_test(&cfqg->ref))
> return;
> for_each_cfqg_st(cfqg, i, j, st)
> - BUG_ON(!RB_EMPTY_ROOT(&st->rb) || st->active != NULL);
> + BUG_ON(!RB_EMPTY_ROOT(&st->rb));
> kfree(cfqg);
> }
>
> @@ -1687,9 +1678,6 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
> if (cfqq == cfqd->active_queue)
> cfqd->active_queue = NULL;
>
> - if (&cfqq->cfqg->rb_node == cfqd->grp_service_tree.active)
> - cfqd->grp_service_tree.active = NULL;
> -
> if (cfqd->active_cic) {
> put_io_context(cfqd->active_cic->ioc);
> cfqd->active_cic = NULL;
> @@ -2199,7 +2187,6 @@ static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd)
> if (RB_EMPTY_ROOT(&st->rb))
> return NULL;
> cfqg = cfq_rb_first_group(st);
> - st->active = &cfqg->rb_node;
> update_min_vdisktime(st);
> return cfqg;
> }
> --
> 1.6.5.2
>
>
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