netdev - Re: Possible regression in HTB

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Message-ID: <20081008072203.GJ22396@verge.net.au>
Date:	Wed, 8 Oct 2008 18:22:04 +1100
From:	Simon Horman <horms@...ge.net.au>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Martin Devera <devik@....cz>
Subject: Re: Possible regression in HTB

On Wed, Oct 08, 2008 at 06:55:51AM +0000, Jarek Poplawski wrote:
> On Wed, Oct 08, 2008 at 02:31:26AM +0200, Patrick McHardy wrote:
> ...
> > I'm pretty sure that the differences are caused by HTB not being
> > in control of the queue since the device is the real bottleneck
> > in this configuration.
> 
> Yes, otherwise there would be no requeuing. And, btw. the golden rule
> of scheduling/shaping is limiting below "hardware" limits.
> 
> > Its quite possible that there simply might
> > a subtle timing change that causes feedback through HTBs borrowing
> > and ceiling.
> 
> I'd add my previous suspicion there could be not enough enqeuing on
> time for the fastest class (could be also very bursty), so other
> classes can borrow more.
> 
> >
> > So what would really be useful to understand this is to make HTB
> > control the queue and see if it behaves as expected.
> >
> 
> Right, trying with lower rates/ceils should explain this.

As I mentioned earlier things seem to work quite well with lower
rates/ceilings. When I set up the classes with 10x lower values
for rate and celing, as follows:


                           [ rate=100Mbit/s ]
                           [ ceil=100Mbit/s ]
                                  |
             +--------------------+--------------------+
             |                    |                    |
      [ rate= 50Mbit/s ]   [ rate= 10Mbit/s ]   [ rate= 10Mbit/s ]
      [ ceil=100Mbit/s ]   [ ceil=100Mbit/s ]   [ ceil= 100Mbit/s ]

Then I get results that are fairly close to the ideal values.

net-next-2.6 - d877984
----------------------
10194: 68075482bits/s 68Mbits/s
10197: 14464848bits/s 14Mbits/s
10196: 14465632bits/s 14Mbits/s
-----------------------------------
total: 97005962bits/s 97Mbits/s

And I get those kind of results consistently for various
different kernel versions.


-- 
Simon Horman
  VA Linux Systems Japan K.K., Sydney, Australia Satellite Office
  H: www.vergenet.net/~horms/             W: www.valinux.co.jp/en

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