linux-kernel - Re: [PATCHSET] blk-throttle: implement proper hierarchy support

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Message-ID: <20130502173428.GA4771@redhat.com>
Date:	Thu, 2 May 2013 13:34:28 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org, lizefan@...wei.com,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org
Subject: Re: [PATCHSET] blk-throttle: implement proper hierarchy support

On Wed, May 01, 2013 at 05:39:18PM -0700, Tejun Heo wrote:

[..]
> While this patchset contains many patches, the implementation is
> pretty straight-forward.  throtl_grp's form a tree anchored at
> throtl_data and bios climb the tree as they get dispatched at each
> level.  The bios which reach the top of the tree - throl_data - are
> issued. 

Have a question here. Looks like when bio climbs from child group
to parent group, then parent group slice starts fresh if parent
was empty. So if we have a parent with 1MB/s limit and a child with
1MB/s limit and a bio gets queued in child, then looks like effective
IO rate would be .5MB/s and not 1MB/s?

IOW, when child gets queued, we should start time accounting for
all parents in the hiearchy too.

Thanks
Vivek
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