Hi, Can you attach a basic topology diagram, showing the ports with the performance problem, and how they are connected?
Are the inter-switch ports showing any discards or errors?
Are the inter-switch ports part of a port channel? Is there mlag configured on these inter-switch ports?
You wrote:
"When the same 40G port sends traffic to a 10G port located on the same switch, the performance is very good, nearly line speed (9.9Gb/s)."
Did you do this same test on "both" switches?