On 8 Jul 2019, at 14:53, Rastislav Szabo -X (raszabo - PANTHEON TECHNOLOGIES at Cisco) <raszabo@cisco.com> wrote:

The test is a simple iperf TCP – single client, single server, within the same node (via VPP vswitch), no NAT is involved (although it is configured). The MTU on the tap interfaces is set to 1450 in this case, but the same can be reproduced with 9000 as well. Now the issue is: the performance is very poor (few Mbits/s), and the trace contains drops as the follows. What is even more strange, we have an automated test which tries similar iperf, and it workrs for that one (> 10 Gbits/s). Could you please take a look at what is happening in this case?

Packet drops because of exceeding MTU – should that even happen if GSO is enabled?