Full 40Gbps with i40e for large packets?

Hi,

Using the xdpsock txonly benchmark in zero-copy mode with the i40e
driver, I get ~22 Mpps for 64 Byte packets.

However, for 1518 byte packets, although the theoretical pps rate for
40Gbps is ~3.25 Mpps (which is much lower than 22 Mpps), I am not able
to get the full rate - only around 39G or 39.5Gbps (i.e. < 3.25Mpps).
My assumption is AF_XDP performance is more pps dependent than packet
size related and so I thought full 40G should be achievable.

Settings:
 * tuned set to "throughput performance"
 * hardware tx ring size set to 512 descriptors - increasing it to up
to the max of 4096 doesn't have any noticeable changes

Increasing the packet size to 3000 or 4096 does bump up the Gbps rate
to around 39.9Gbps.

Is there a way to get the full 40Gbps (or close, say 39.9Gbps) tx rate
with 1518 byte packets?

Srivats