linux-kernel - Re: [PATCH 12/24] cfq-iosched: implement cfq_group->nr_active and ->children

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Date:	Tue, 8 Jan 2013 10:51:14 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	lizefan@...wei.com, axboe@...nel.dk,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, ctalbott@...gle.com, rni@...gle.com
Subject: Re: [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 <tj@...nel.org>
> Cc: Vivek Goyal <vgoyal@...hat.com>

Looks good to me.

Acked-by: Vivek Goyal <vgoyal@...hat.com>

Vivek
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