Setpci unable to change the PCIe maximum read request and payload values

Hi there,

I’m setting up the Mellanox CX-5 (MCX515A-CCAT) NIC for my server with Ubuntu 20.04 LTS. When running a traffic generator, It can only achieve 60% of the line rate speed (in the order of 90Mpps with 64B packets). By reading the DPDK manual, I knew that changing the PCIe MaxPayload and MaxReadReq might be helpful.

As recommended, I first checked out the current value with setpci -s 0b:00.0 68.w, the value was 0000 (the value is actually pretty wired). When I used setpci -s 0b:00.0 68.w=3000 to change the MaxReadReq from 128 bytes to 512 bytes, it completed without error (echo $? give 0). However, when I rechecked the value with setpci -s 0b:00.0 68.w, the value was still 0000 without any changes.

I totally have no idea what was wrong in my configurations. Could anyone help me with this? Thanks in advance.

Wendi