The System Activity page at Diagnostics > System Activity displays CPU usage, memory usage, swap usage, and the processes and threads using the most CPU time.
Those familiar with the console will recognize this as the output of “top -aSH”. Like top on the console, this output is updated every few seconds. However, the version of the output shown in the GUI is not capable of displaying the CPU usage summary at the top of the list.
NOTE: Threads that show idle in the COMMAND column indicate CPU time that is not in use (idle). It is normal for these to show 100% if the firewall has little to no load.