cfq-iosched: convert cfq_group_slice() to use cfqg->vfraction

cfq_group_slice() calculates slice by taking a fraction of
cfq_target_latency according to the ratio of cfqg->weight against
service_tree->total_weight.  This currently works only because all
cfqgs are treated to be at the same level.

To prepare for proper hierarchy support, convert cfq_group_slice() to
base the calculation on cfqg->vfraction.  As cfqg->vfraction is always
a fraction of 1 and represents the fraction allocated to the cfqg with
hierarchy considered, the slice can be simply calculated by
multiplying cfqg->vfraction to cfq_target_latency (with fixed point
shift factored in).

As vfraction calculation currently treats all non-root cfqgs as
children of the root cfqg, this patch doesn't introduce noticeable
behavior difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index b24acf66d5b545a5dd2f24e3c5ab65c807c8c080..ee342826fd98e89a877c8a76e60bb016689047ca 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -85,7 +85,6 @@ struct cfq_rb_root {
        struct rb_root rb;
        struct rb_node *left;
        unsigned count;
-       unsigned total_weight;
        u64 min_vdisktime;
        struct cfq_ttime ttime;
 };
@@ -979,9 +978,7 @@ static inline unsigned cfq_group_get_avg_queues(struct cfq_data *cfqd,
 static inline unsigned
 cfq_group_slice(struct cfq_data *cfqd, struct cfq_group *cfqg)
 {
-       struct cfq_rb_root *st = &cfqd->grp_service_tree;
-
-       return cfqd->cfq_target_latency * cfqg->weight / st->total_weight;
+       return cfqd->cfq_target_latency * cfqg->vfraction >> CFQ_SERVICE_SHIFT;
 }
 
 static inline unsigned
@@ -1273,7 +1270,6 @@ cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
 
        cfq_update_group_weight(cfqg);
        __cfq_group_service_tree_add(st, cfqg);
-       st->total_weight += cfqg->weight;
 
        /*
         * Activate @cfqg and calculate the portion of vfraction @cfqg is
@@ -1360,7 +1356,6 @@ cfq_group_service_tree_del(struct cfq_rb_root *st, struct cfq_group *cfqg)
        }
 
        /* remove from the service tree */
-       st->total_weight -= cfqg->weight;
        if (!RB_EMPTY_NODE(&cfqg->rb_node))
                cfq_rb_erase(&cfqg->rb_node, st);
 }