[dpdk-users] Interesting considerate but annoying behavior of MLX5 driver

Wu, Xiaoban Xiaoban_Wu at student.uml.edu
Fri Apr 27 00:26:36 CEST 2018

Dear All,

I have two Dell PowerEdge R740 servers A and B running with ubuntu 16.04, each one has a Mellanox MCX556A-ECAT NIC installed on the PCIe x16 slot. And, the two NICs are directly connected back to back with a copper cable.

On server A, it runs a RX program which runs a function to process and analyze the received packets. On server B, it runs a packet-gen program which generates and sends packets out. They are both compiled with dpdk-17.11

Now the interesting thing is that on server B, it is kind of smart and considerate enough to automatically adjust its TX throughput according to how fast server A processes the packets. If server A processes the packets faster, then server B sends packets with a higher throughput. Similarly, if server A processes the packets slower, then server B sends packets with a lower throughput. Please note that once the program on server B starts, it is never interrupted by any way.

However, I think the server B should send out the packets with a constant throughput no matter how fast server A processes the packets.

Does anybody else notice this interesting behavior of MLX5 driver? Can anybody help me disable this feature permanently? Thanks very much for your help.

Best wishes,


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