[Cake] dual-src/dsthost unfairness, only with bi-directional traffic

[Pete Heist]

> On Jan 3, 2019, at 2:02 PM, Pete Heist <pete at heistp.net> wrote:
> 
> I tried iperf3 in UDP mode, but cake is treating these flows aggressively. I get the impression that cake penalizes flows heavily that do not respond to congestion control signals. If I pit one 8 TCP flows against a single UDP flow at 40mbit, the UDP flow goes into a death spiral with increasing drops over time (iperf3 output attached).

Sigh, this spiraling was partly because iperf3 in UDP mode sends 8k buffers by default. If I use “-l 1472” with the iperf3 client, the send rates are the same, but the packet loss is much lower, without interplanetary. So one more result:

	IP1 1-flow TCP up: 49 - 59.5
	IP2 8-flow UDP 48-mbit up: 48 - 36 (loss 0% - 25%)
	IP1 8-flow UDP 48-mbit down: 47.5 - 35.8 (loss 0% - 25%)
	IP2 1-flow TCP down: 21.8 - 61.5

I do see the rates and loss gradually change over 60 seconds, so numbers are shown at t=0 and t=60 seconds.

I’ve read that nuttcp does UDP bulk flows better than iperf3, so one day I may try that.