Bad TCP performance on WLE900VX

[Robert Jones]

Hello Everyone,

I'm using a custom arm64 board with a Cavium CN8030 CPU and testing
wireless card performance via iperf on Ubuntu 16.02 with a mainline
4.14 kernel. I have two identical units connected to each other via
60dB attenuators on all three channels. Channel is set to 161 VHT80.

With UDP I see throughput upwards of 650Mbits/s, but TCP is
~24Mbits/s. That seemed odd so I did a little more testing. Switched
to a 4.9 kernel and still saw the poor performance, but not with a
4.4. Before I went through the trouble of bisecting I thought to ask
if there was something I was missing.

I did come across this Ubuntu bug thread
[https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1670041] which
appeared to follow the same behavior I was seeing. Switched my TCP
congestion algorithm to reno and saw throughput jump to >330Mbits/s.
Cubic and BBR still ~24.

My question now, is there a standing bug that I'm not aware of or
could there be some sort of problem with my configuration that is
being worked around with the reno algorithm?

Thanks,
Robert Jones