Thank you for posting your inquiry to the Mellanox community.
We will need some further information in order to assist you further:
What is the part number of the HCA in question? This can be obtained via:
lspci -d 15b3: -vv | grep PN
What firmware revision is installed on the HCA?
What OS and kernel version is installed on this system?
Are you using MLNX_OFED, or inbox (upstream OS) drivers?
You mention that you are not able to use multi-core - could you elaborate as to what you mean by that? What steps are you taking in order to configure RSS?
Thank you, and we look forward to hearing from you soon.