Running iperf3 as a server drops all connections to a machine

[Pete French]

This is odd - I have six FreeBSD boxes on the local ether here. Five are
HP Microservers, one is an AMD Ryzen. They are all running 12.1 r352847
built yesterday - and its one compilation I did which is rsynced out to
all the machines, so an identical build.

I was running iperf3 -s on one machine and iperf3 -c on another to measure
TCp/IP rates as I am experimenting with the RACK version of the
stack and using CUBIC as a congetion control algorithm. All goes
well between the Intel boxes, and if I use the Ryzen box as a client ot
the Intel boxes. But if I run the iperf3 server on the Ryzemn box
and use one of the Intel boxes as a client then after a few seconds
all the TCP connection on the Ryzen box are dropped. There is nothing
in dmesg, no indication that I can find of anything going wrong, and
I can immediately ssh back in.

On the client side it looks like this:

[webadmin at dogbert ~]$ iperf3 -c dilbert
Connecting to host dilbert, port 5201
[  5] local 10.64.50.50 port 41134 connected to 10.64.50.6 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   112 MBytes   938 Mbits/sec    1   78.2 KBytes       
[  5]   1.00-2.00   sec   112 MBytes   936 Mbits/sec    2   54.8 KBytes       
[  5]   2.00-3.02   sec  14.7 MBytes   122 Mbits/sec    3   1.43 KBytes       
[  5]   3.02-4.00   sec  0.00 Bytes  0.00 bits/sec    2   1.43 KBytes       
[  5]   4.00-5.02   sec  0.00 Bytes  0.00 bits/sec    1   1.43 KBytes       
[  5]   5.02-6.02   sec  0.00 Bytes  0.00 bits/sec    1   1.43 KBytes       
[  5]   5.02-6.02   sec  0.00 Bytes  0.00 bits/sec    1   1.43 KBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-6.02   sec   238 MBytes   332 Mbits/sec   10             sender
[  5]   0.00-6.02   sec  0.00 Bytes  0.00 bits/sec                  receiver
iperf3: error - the server has terminated
[webadmin at dogbert ~]$

...and on the server side, this...

petefrench at dilbert ~]$ iperf3 -s
-----------------------------------------------------------
Server listening on 5201
-----------------------------------------------------------
Accepted connection from 10.64.50.50, port 41133
[  5] local 10.64.50.6 port 5201 connected to 10.64.50.50 port 41134
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.00   sec   105 MBytes   883 Mbits/sec                  
[  5]   1.00-2.00   sec   112 MBytes   936 Mbits/sec                  
[  5]   2.00-3.01   sec  21.3 MBytes   177 Mbits/sec                  
Connection to dilbert.ingresso.co.uk closed by remote host.
Connection to dilbert.ingresso.co.uk closed.

This only happens on the Ryzen machine. It happens whether I am using
the RACk stack or the default one, and whether I am using CUBIC or the
default too.

The system is build with CPUTYPE set to 'core2' and some modules skipped,
but apart from that nothing special.

Its a bit worrying to me that this can happen, especially in userland.

Any opinions or things people would ike me to check ? Indeed, can anyone
reproduce this ?

cheers,

-pete.