tap device speed

[Antonio Di Bacco <a.dibacco.ks@gmail.com>]

I'm doing a test where we have a couple of tap devices, the two
devices are seen by testpmd that is setup in forward mode.

On the linux side, the two tap devices are confined in different
network namespaces and in one namespace we have an iperf server while
on the other namespace the iperf client sending either UDP or TCP.

I expected a bandwidth in the range of few gpbs while the actual
measured bandwidth is a few gigabits.

I suppose I need to configure the tap devices with optimized
parameters but I don't know where to look for advice.

If I try to use the loopback interface I can get something 40 gbps
with a command like this:

iperf -c 127.0.0.1 -u -i 1 -b 40g -t 10 -l 40000

.