iperf 2.2.0 is out:
https://lore.kernel.org/all/dad9030c7a57d93220503ef4411af89b@rjmcmahon.com/
"'Lots of features & bug fixes and hopefully on a few regressions. Big focus around latency and buffer depths, .e.g support for inflight on the client and in progress (per Little's Law) on the server.'"