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

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Date:	Wed, 4 Jul 2012 18:51:32 +0200
From:	Hagen Paul Pfeifer <hagen@...u.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
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

* Eric Dumazet | 2012-07-04 07:58:08 [+0200]:


>DEV=eth0
>tc qdisc del dev $DEV root
>tc qdisc add dev $DEV root handle 30: est 1sec 4sec netem \
>        delay 100ms 10ms reorder 3
>tc qdisc add dev $DEV handle 40:0 parent 30:0 tbf \
>        burst 5000 limit 10000 mtu 1514 rate 100kbit
>tc qdisc add dev $DEV handle 50:00 parent 40:0 pfifo limit 200
>
>fundamentally, mixing the TBF is going to be hard with "delay ..."
>especially with jitter.
>
>Same problem for reorder : since packets are put at head of queue,
>they have no effect on the 'time_to_send' of packets already in queue
>and netem use more bandwidth than allowed.
>
>I'll send the patch on the double drop accounting problem because the
>fix is easy enough, but fir the rate limiting, I prefer letting you work
>on it if you dont mind ?

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!

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?
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