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cfq-iosched: enable full blkcg hierarchy support

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With the previous two patches, all cfqg scheduling decisions are based
on vfraction and ready for hierarchy support.  The only thing which
keeps the behavior flat is cfqg_flat_parent() which makes vfraction
calculation consider all non-root cfqgs children of the root cfqg.

Replace it with cfqg_parent() which returns the real parent.  This
enables full blkcg hierarchy support for cfq-iosched.  For example,
consider the following hierarchy.

        root
      /      \
   A:500      B:250
  /     \
 AA:500  AB:1000

For simplicity, let's say all the leaf nodes have active tasks and are
on service tree.  For each leaf node, vfraction would be

 AA: (500  / 1500) * (500 / 750) =~ 0.2222
 AB: (1000 / 1500) * (500 / 750) =~ 0.4444
  B:                 (250 / 750) =~ 0.3333

and vdisktime will be distributed accordingly.  For more detail,
please refer to Documentation/block/cfq-iosched.txt.

v2: cfq-iosched.txt updated to describe group scheduling as suggested
    by Vivek.

v3: blkio-controller.txt updated.

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 41cad6ab2c
commit d02f7aa8dc
3 changed files with 88 additions and 26 deletions
Download Patch File Download Diff File Expand all files Collapse all files
block/cfq-iosched.c
+6 -15
View File
@@ -606,20 +606,11 @@ 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)
static inline struct cfq_group *cfqg_parent(struct cfq_group *cfqg)
{
struct blkcg_gq *blkg = cfqg_to_blkg(cfqg);
struct cfq_group *root;
struct blkcg_gq *pblkg = cfqg_to_blkg(cfqg)->parent;
while (blkg->parent)
blkg = blkg->parent;
root = blkg_to_cfqg(blkg);
return root != cfqg ? root : NULL;
return pblkg ? blkg_to_cfqg(pblkg) : NULL;
}
static inline void cfqg_get(struct cfq_group *cfqg)
@@ -722,7 +713,7 @@ 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 struct cfq_group *cfqg_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) { }
@@ -1290,7 +1281,7 @@ cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
* stops once an already activated node is met. vfraction
* calculation should always continue to the root.
*/
while ((parent = cfqg_flat_parent(pos))) {
while ((parent = cfqg_parent(pos))) {
if (propagate) {
propagate = !parent->nr_active++;
parent->children_weight += pos->weight;
@@ -1341,7 +1332,7 @@ cfq_group_service_tree_del(struct cfq_rb_root *st, struct cfq_group *cfqg)
pos->children_weight -= pos->leaf_weight;
while (propagate) {
struct cfq_group *parent = cfqg_flat_parent(pos);
struct cfq_group *parent = cfqg_parent(pos);
/* @pos has 0 nr_active at this point */
WARN_ON_ONCE(pos->children_weight);