Would suggest that you start first with:
1. “Performance Tuning” for Mellanox Adapters & driver, to ensure you have proper BIOS configuration, to check the cpu core frequency and that you use PCIe generation that suit the adapter etc…
https://community.mellanox.com/docs/DOC-2489#jive_content_id_Getting_started
2. Check the Mellanox inbox driver by using "esxcli software vib list |grep nmlx4" command.
for example:
# esxcli software vib list |grep nmlx4
Name Version Vendor Acceptance Level Install Date
----------------------------- ------------------------------------ ------ ---------------- ------------
nmlx4-core 3.0.0.0-1vmw.600.0.0.2494585 VMware VMwareCertified 2015-12-16
nmlx4-en 3.0.0.0-1vmw.600.0.0.2494585 VMware VMwareCertified 2015-12-16
nmlx4-rdma 3.0.0.0-1vmw.600.0.0.2494585 VMware VMwareCertified 2015-12-16
3. Assuming that the56Gb nic is up check the netqueue is enabled by default.
4. Set nmlx4_en module parameters num_rings_per_rss_queue to 4.
# esxcli system module parameters set -m nmlx4_en -p "num_rings_per_rss_queue=4"
# reboot
# esxcli system module parameters list -m nmlx4_en
In case the suggested above is implemented and you still have low performance, then apply to Mellanox support (support@mellanox.com) to get further assistance on this