Intel 10-Gigabit X540-AT2 (rev 01) Bandwidth Not as spec

Hello Intel,

We have purchased 3pcs of Intel Corporation Ethernet Controller 10-Gigabit X540-AT2 (rev 01).

We have connected this to our HP Desktops in the PCI Express slot(PCI bridge: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor PCI Express x16 Controller (rev 06)).

Now when we run iperf tool to measure the bandwidth we found that when dual port are used to tx/rx we see total bandwidth as 1st port @~4Gbits/sec and 2nd port @~5Gbits/sec total for 2 ports(port1 + port2) @~9Gbits/sec

When we use only 1 port we see 9Gbps bandwidth.

But as the product spec details from the link (Intel® Ethernet Converged Network Adapter X540-T2 Product Specifications ) as per port 10Gbps.

Please help us to reach the bandwidth as mentioned in the product spec. Means are we doing something wrong or any configuration in the driver that we need do.

Attachments shows how we are connected and tests performed with the results.

Thanks in advance.