Ubuntu – Why % CPU doesn’t add up to 100

cpu loadprocesssystem-monitor

Why doesn't the "% CPU" in System Monitor add up to 100? (% CPU is the third column on the following screenshot)

cpu time

Best Answer

Two reasons:

  1. The calculations are per-core. So if you have a dual-core system then the maximum will be 200%.
  2. You will not necessarily see all processes which are using your CPU in System Monitor, so the CPU usage might be below 100% for each processor.

Furthermore it is unusual for 100% of any processor to be in use. See the resources tab for the total in use per processor.

Related Question