Why is there a difference in speed of forward and reverse traffic over 10 G network in iperf tool

I have a 10G network setup between my two servers (say, Server1 and Server2) and I'm using iperf tool to measure the bandwidth of the network. Here are test cases that I performed,

Test Case 1: (Forward Data Transfer)

Making Server 1 as iperf server and Server 2 as iperf client.

[ ID] Interval       Transfer     Bandwidth
[  4] 0.0-10.0 sec   8.81 GBytes  7.56 Gbits/sec

Test Case 2: (Reverse Data Transfer)

Making Server 2 as iperf server and Server 1 as iperf client.

[ ID] Interval       Transfer     Bandwidth
[  4] 0.0-10.1 sec  1.05 GBytes   893 Mbits/sec

Moreover, I've the same configuration on both servers.

OS: Redhat 7.4

MTU: 9000 bytes

10G network card information (via ethtool) on both server are also same.

Settings for em2:
        Supported ports: [ TP ]
        Supported link modes:   100baseT/Full
                                1000baseT/Full
                                10000baseT/Full
        Supported pause frame use: Symmetric
        Supports auto-negotiation: Yes
        Advertised link modes:  100baseT/Full
                                1000baseT/Full
                                10000baseT/Full
        Advertised pause frame use: Symmetric
        Advertised auto-negotiation: Yes
        Speed: 10000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 0
        Transceiver: external
        Auto-negotiation: on
        MDI-X: Unknown
        Supports Wake-on: umbg
        Wake-on: g
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: yes

Network Switch: SG350XG-2F10 12-Port 10G Stackable Managed Switch

Here's the network connectivity diagram for better understanding.

Can anyone suggest why there is a difference in speeds of the forward vs the reverse traffic?

Not sure what's the cause. What version of iperf are you running on both the client and server. iperf -v should provide this.

Can you try iperf 2.0.14a after a fresh compile? Note, this code is still under development. This may or may not help answer your question.

Bob