Unstable iperf3 results with strange cpu usage

[zgdump]

On my machines, on any network interface in Haiku, files are downloaded very slowly, and heavy ones cannot be downloaded at all. The speed hardly exceeds 600-700 kilobytes. I was offered to run and test iperf3 over localhost and:

TCP is very unstable. $ iperf3 -c localhost -R -t 100

See screenshot_tcp.png and strange_loop_consumer_behaviour.mp4

UDP is stable, but consuming too much CPU. $ iperf3 -c localhost -R -t 100 -u -b 0

See screenshot_udp.png

Each screenshot also shows the Activity Monitor.

Ifconfig and About are also included