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Commit 7918ffb5 authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarVivek Goyal <vgoyal@redhat.com>
parent e71357e1

block/cfq-iosched.c

+76 −0
Original line number Diff line number Diff line
@@ -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);