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authorTejun Heo <tj@kernel.org>2013-01-09 08:05:11 -0800
committerTejun Heo <tj@kernel.org>2013-01-09 08:05:11 -0800
commit7918ffb5b83e3373206ada84873c674fbddf61cc (patch)
treed7b2fe17efe9453fbb1afbfad8c7fc0e7a6bb01b /block
parente71357e118bdd4057e3bc020b9d80fecdd08f588 (diff)
downloadlinaro-lsk-7918ffb5b83e3373206ada84873c674fbddf61cc.tar.gz
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>
Diffstat (limited to 'block')
-rw-r--r--block/cfq-iosched.c76
1 files changed, 76 insertions, 0 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 175218d66d6..7701c3fe49b 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -225,6 +225,18 @@ struct cfq_group {
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
* this cfqg against the child cfqgs. For the root cfqg, both
@@ -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);