Monitoring CPU activity can be effectively done by focusing on just two statistics: CPU busyness and CPU queue length. The more common term for CPU busyness is utilization. A CPU subsystem has a single run queue.

Utilization is an amazingly simple concept that can be applied in a wide variety of circumstances. It is simply consumption divided by capacity. For example, if we have an empty pitcher with the capacity of four cups, and it currently contains two cups of water, the utilization is 50%. It's not rocket science, but this basic concept is used throughout performance management, both in firefighting and predictive analyses of all kinds.

Gathering CPU utilization statistics is easy, and there are a number of sources, including one of Oracle's performance views. While each operating system has its own specific tools, vmstat is nearly always available, and sometimes you can use sar.