What does CPU usage over 100% mean?

RPM displays your CPU usage as a percentage, but this percentage can go over 100%. The reason for this is somewhat complicated, but what it means is that you can compare CPU numbers when you change the number of cores on your servers.

The percentage is calculated by one CPU's usage times number of CPUs total. We actually base it on CPU time divided by wall clock time, which, in the case of 4 CPUs, runs CPU time 4x as fast as real time.

The reason we do it this way is for processor upgrades: going from (say) a dual processor to a quad processor, you should see roughly the same CPU numbers, for the same load and app. (assuming your server architecture is the same, of course)

If we normalized, you'd see an abrupt decrease in your CPU usage, even though the actual number of cycles you're using is exactly the same. That seems unrealistic, so we go with the un-normalized number.