linux-kernel - Re: [PATCH 06/12] cfq-iosched: implement cfq_group->nr_active and ->level

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Message-ID: <20121217211517.GC1844@htj.dyndns.org>
Date:	Mon, 17 Dec 2012 13:15:17 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
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 06/12] cfq-iosched: implement cfq_group->nr_active and
 ->level_weight

Hello, Vivek.

On Mon, Dec 17, 2012 at 03:46:09PM -0500, Vivek Goyal wrote:
> On Fri, Dec 14, 2012 at 02:41:19PM -0800, Tejun Heo wrote:
> > To prepare for blkcg hierarchy support, add cfqg->nr_active and
> > ->level_weight.  cfqg->nr_active counts the number of active cfqgs at
> > the cfqg's level and ->level_weight is sum of weights of those cfqgs.
> > The level covers itself (cfqg->leaf_weight) and immediate children.
> 
> This notion of level is really confusing. If one says "at cfqg's level"
> I immediately associate with cfqg's siblings and not with cfqg's children.

We can explicitly say at children's level but I think it should be
enough to explain it clearly in the comment where the field is
defined.

> I think confusion happens because we are overloading the definition of
> cfqg. It is competing with its siblings at the same time it is competing
> against its child groups (on behalf of its children tasks).

While I agree that part is a bit tricky, I can't think of a much
better way to describe it.  Any better ideas?

Thanks.

-- 
tejun
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