Hi Andi!

quoted

Important note: we ARE able to get full duplex wire speed (over 900
Mb/s simulaneously in both directions) using UDP.  The problems occur
only with TCP connections.

Another issue with full duplex TCP not mentioned yet is that if TSO is used
the output  will be somewhat bursty and might cause problems with the
TCP ACK clock of the other direction because the ACKs would need
to squeeze in between full TSO bursts.

You could try disabling TSO with ethtool.

Noted.  We'll try this also.

Cheers,
 	Bruce