Transmit rate decreases when using both Intel NIC 10G ports

[hjazz6]

Hi all,

I'm using the Intel 82599EB 10G NIC on a server running RHEL6. I ran a program where packets are generated at high rates. The NIC was previously installed on another PC where I was able to generate traffic at 8-9Gbps on each port concurrently. On this server, I was able to generate at 8-9Gbps only if one port is in use. If I were to generate on both ports concurrently, then my total transmit rate drops to about 12Gbps (~6Gbps on each port).

My relevant "lspci -vvv" output shows the following:

0b:00.0 Ethernet controller: ...
      Capabilities: [a0] Express (v2) Endpoint, MSI 00
            LnkCap: Port #1, Speed 5GT/s, Width x8
            LnkSta: Speed 5GT/s, Width x4
            LnkCtl2: Target Link Speed: 5GT/s

0b:00.1 Ethernet controller: ...
      Capabilities: [a0] Express (v2) Endpoint, MSI 00
            LnkCap: Port #1, Speed 5GT/s, Width x8
            LnkSta: Speed 5GT/s, Width x4
            LnkCtl2: Target Link Speed: 2.5GT/s

Is my transmit rate limited by the "x4" in LnkSta for both ports? And what does it mean to have "Target Link Speed: 5GT/s" on one port and "Target Link Speed: 2.5GT/s" on the other port? Does this contribute to the rate decrease too?

Also, I see a couple of PCIE slots that are longer than my NIC's PCIE connectors. Can I install my NIC on these longer slots instead?

Thank you.

Regards,
Rayne

[karthik_arnold1]

Check the link speed on the nic .

ethtool eth0

Check if the link is 10gbps or 1 gbps and also check the duplex settings on both the switch and nic .