Mellanox ConnectX-5 adapter speed 650MB/s only

Helllo,

I have two Mellanox Connectx-5 adapters connected back to back. Link speed shows 40Gbps. I am using widows server 2016. Tried with different PCIe slots and tested with iperf3. But in case of TCP speed reaches up to 650 MB/s only and in UDP it only achieves nearby 450 MB/s.

I am sure I am missing out some setting but can not figure out what.

Can anybody help me in this case?

Could you try this:

Thank you. I tried NTttcp with different send buffer size and datagram size. I was able to get 4.8 GBytes speed on 40Gbps link.