Performance on 10G / 1500 MTU link

[Luki Goldschmidt]

Hi,

Has anyone succeeded in saturating a 10Gb link with a MTU 1500 using
WireGuard?

On a LAN with 10Gb or 40Gb links, I'm getting 5-6 Gbps throughput with
WireGuard (tunnel MTU 1420). Without WireGuard, I have no problem
pushing 9.8 and 35 Gbps, respectively. When I increase the tunnel MTU to
8920, I can easily push 9.3 Gbps through Wireguard.

I'm testing testing with iperf using a single or multiple parallel
transfers. I tried kernels 5.14 and 5.15, and a range of CPUs like Intel
E5-2680v4, E3-1270v6, Xeon Silver 4114. The bottleneck seems to linked
to packets per second.

I can't use jumbo frames over the WAN connection so MTU 1500 (link) will
have to be it, but I'd love to get the most out of the 10 Gbps
connection. The WAN link latency is only ~1 ms so it ought to be doable.

Any tuning tips are appreciated.

Luki