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SubjectRe: [PATCH 12/24] cfq-iosched: implement cfq_group->nr_active and ->children_weight
On Fri, Dec 28, 2012 at 12:35:34PM -0800, Tejun Heo wrote:
> 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 <>
> Cc: Vivek Goyal <>

Looks good to me.

Acked-by: Vivek Goyal <>


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