linux-kernel - Re: [PATCH 14/24] cfq-iosched: convert cfq_group

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Message-ID: <20130108164226.GE29635@redhat.com>
Date:	Tue, 8 Jan 2013 11:42:26 -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 14/24] cfq-iosched: convert cfq_group_slice() to use
 cfqg->vfraction

On Fri, Dec 28, 2012 at 12:35:36PM -0800, Tejun Heo wrote:
> cfq_group_slice() calculates slice by taking a fraction of
> cfq_target_latency according to the ratio of cfqg->weight against
> service_tree->total_weight.  This currently works only because all
> cfqgs are treated to be at the same level.
> 
> To prepare for proper hierarchy support, convert cfq_group_slice() to
> base the calculation on cfqg->vfraction.  As cfqg->vfraction is always
> a fraction of 1 and represents the fraction allocated to the cfqg with
> hierarchy considered, the slice can be simply calculated by
> multiplying cfqg->vfraction to cfq_target_latency (with fixed point
> shift factored in).
> 
> As vfraction calculation currently treats all non-root cfqgs as
> children of the root cfqg, this patch doesn't introduce noticeable
> behavior difference.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>

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

Vivek
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