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cfq-iosched: implement cfq_group->nr_active and ->children_weight 

To prepare for blkcg hierarchy support, add cfqg->nr_active and
->children_weight.  cfqg->nr_active counts the number of active cfqgs
at the cfqg's level and ->children_weight is sum of weights of those
cfqgs.  The level covers itself (cfqg->leaf_weight) and immediate
children.

The two values are updated when a cfqg enters and leaves the group
service tree.  Unless the hierarchy is very deep, the added overhead
should be negligible.

Currently, the parent is determined using cfqg_flat_parent() which
makes the root cfqg the parent of all other cfqgs.  This is to make
the transition to hierarchy-aware scheduling gradual.  Scheduling
logic will be converted to use cfqg->children_weight without actually
changing the behavior.  When everything is ready,
blkcg_weight_parent() will be replaced with proper parent function.

This patch doesn't introduce any behavior chagne.

v2: s/cfqg->level_weight/cfqg->children_weight/ as per Vivek.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
This commit is contained in:
Tejun Heo 2013-01-09 08:05:11 -08:00
parent e71357e118
commit 7918ffb5b8
1 changed files with 76 additions and 0 deletions
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76
block/cfq-iosched.c
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@ -224,6 +224,18 @@ struct cfq_group {
/* group service_tree key */
u64 vdisktime;
/*
* The number of active cfqgs and sum of their weights under this
* cfqg. This covers this cfqg's leaf_weight and all children's
* weights, but does not cover weights of further descendants.
*
* If a cfqg is on the service tree, it's active. An active cfqg
* also activates its parent and contributes to the children_weight
* of the parent.
*/
int nr_active;
unsigned int children_weight;
/*
* There are two weights - (internal) weight is the weight of this
* cfqg against the sibling cfqgs. leaf_weight is the wight of
@ -583,6 +595,22 @@ static inline struct cfq_group *blkg_to_cfqg(struct blkcg_gq *blkg)
return pd_to_cfqg(blkg_to_pd(blkg, &blkcg_policy_cfq));
}
/*
* Determine the parent cfqg for weight calculation. Currently, cfqg
* scheduling is flat and the root is the parent of everyone else.
*/
static inline struct cfq_group *cfqg_flat_parent(struct cfq_group *cfqg)
{
struct blkcg_gq *blkg = cfqg_to_blkg(cfqg);
struct cfq_group *root;
while (blkg->parent)
blkg = blkg->parent;
root = blkg_to_cfqg(blkg);
return root != cfqg ? root : NULL;
}
static inline void cfqg_get(struct cfq_group *cfqg)
{
return blkg_get(cfqg_to_blkg(cfqg));
@ -683,6 +711,7 @@ static void cfq_pd_reset_stats(struct blkcg_gq *blkg)
#else /* CONFIG_CFQ_GROUP_IOSCHED */
static inline struct cfq_group *cfqg_flat_parent(struct cfq_group *cfqg) { return NULL; }
static inline void cfqg_get(struct cfq_group *cfqg) { }
static inline void cfqg_put(struct cfq_group *cfqg) { }
@ -1208,11 +1237,33 @@ cfq_update_group_weight(struct cfq_group *cfqg)
static void
cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
{
struct cfq_group *pos = cfqg;
bool propagate;
/* add to the service tree */
BUG_ON(!RB_EMPTY_NODE(&cfqg->rb_node));
cfq_update_group_weight(cfqg);
__cfq_group_service_tree_add(st, cfqg);
st->total_weight += cfqg->weight;
/*
* Activate @cfqg and propagate activation upwards until we meet an
* already activated node or reach root.
*/
propagate = !pos->nr_active++;
pos->children_weight += pos->leaf_weight;
while (propagate) {
struct cfq_group *parent = cfqg_flat_parent(pos);
if (!parent)
break;
propagate = !parent->nr_active++;
parent->children_weight += pos->weight;
pos = parent;
}
}
static void
@ -1243,6 +1294,31 @@ cfq_group_notify_queue_add(struct cfq_data *cfqd, struct cfq_group *cfqg)
static void
cfq_group_service_tree_del(struct cfq_rb_root *st, struct cfq_group *cfqg)
{
struct cfq_group *pos = cfqg;
bool propagate;
/*
* Undo activation from cfq_group_service_tree_add(). Deactivate
* @cfqg and propagate deactivation upwards.
*/
propagate = !--pos->nr_active;
pos->children_weight -= pos->leaf_weight;
while (propagate) {
struct cfq_group *parent = cfqg_flat_parent(pos);
/* @pos has 0 nr_active at this point */
WARN_ON_ONCE(pos->children_weight);
if (!parent)
break;
propagate = !--parent->nr_active;
parent->children_weight -= pos->weight;
pos = parent;
}
/* remove from the service tree */
st->total_weight -= cfqg->weight;
if (!RB_EMPTY_NODE(&cfqg->rb_node))
cfq_rb_erase(&cfqg->rb_node, st);