This article explains the CPU utilization shown for IOC card with the command "show chassis fpc" and what it actually refers to.

Information on CPU utilization shown for IOC in "show chassis fpc command" 

The IOC cpu utilization that we see in the "show chassis fpc" command’s output is not based on amount of traffic flowing through the IOC or no. of sessions on the IOC. This value (IOC Utilization) is more of a cumulative value of a management chip inside the card. Comparing the IOC CPU utilization with amount of traffic/no. of sessions on an IOC card is an incorrect approach.