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?