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

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Message-ID: <20130503191418.GC22860@mtj.dyndns.org>
Date:	Fri, 3 May 2013 12:14:18 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>, lkml <linux-kernel@...r.kernel.org>,
	Li Zefan <lizefan@...wei.com>,
	containers@...ts.linux-foundation.org,
	Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCHSET] blk-throttle: implement proper hierarchy support

On Fri, May 03, 2013 at 03:08:23PM -0400, Vivek Goyal wrote:
> 		T1	T2	T3	T4	T5	T6	T7
> parent:			b1	b2	b3		b4 	b5
> child: 		b1	b2	b3		b4	b5	
> 
> 
> So continuity breaks down because application is waiting for previous
> IO to finish. This forces expiry of existing time slices and new time
> slice start both in child and parent and penalty keep on increasing.

It's a problem even in flat mode as the "child" above can easily be
just a process which is throttling itself and it won't be able to get
the configured bandwidth due to the scheduling bubbles introduced
whenever new slice is started.  Shouldn't be too difficult to get rid
of, right?

Thanks.

-- 
tejun
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