netdev - Re: [PATCH] netem: fix rate extension and drop accounting

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Date:	Wed, 04 Jul 2012 19:23:21 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hagen Paul Pfeifer <hagen@...u.net>
Cc:	netdev <netdev@...r.kernel.org>, Yuchung Cheng <ycheng@...gle.com>,
	Andreas Terzis <aterzis@...gle.com>,
	Mark Gordon <msg@...gle.com>
Subject: Re: [PATCH] netem: fix rate extension and drop accounting

On Wed, 2012-07-04 at 18:51 +0200, Hagen Paul Pfeifer wrote:
> OK, I will work on it tomorrow! But Eric, keep in mind that this accumulative
> behavior is intended: think about a hypothetical satellite link with a
> bandwidth (rate) of 1000 byte/s. If you send three 1000 byte consecutively
> packets. The first packet is delayed for 1 second, the second then is
> transmitted after 2 seconds, the third after three seconds and so on. So
> _this_ accumulative behavior is correct. Anyway, I will look at this tomorrow!
> 

I fear you did your tests with no delay on netem.

Try to setup a rate of 100kbit and a delay of 100ms and to really get
full bandwith (100kbit), I am afraid it doesnt work.

Your algo is OK only if no packets are in queue (obviously)

But if you have 2 or 3 packets, the delay are cumulative,
but the delay should be a fixed bias for each packet.


> Thanks Eric!
> 
> PS: one last question: what do you want to test? TBF and netem rate at the
> same time looks, mmhh, special ... ;-) I ask myself what link exhibit this
> characteristic?

TBF as a netem child was the usual way to have delay + rate before your
patch ?

Not sure why you find it special ?


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