This is one of the most important things to learn by any System Admin.; the CPU Load Average.

You can get the value simply by running the command “top” to get you the average value in the last 1 min, 5 min and 15 min.

How can you know whether that load average is high or not? That depends on the number of cores you have on your server, so for example, if you have 1 core, then a max. of load average value of 1 would be ok, although you should be a little concerned when it reaches about 0.7 (70%), if you have 2 cores, then 1.4 would be the max. accepted value …etc.

You can get to know the number of cores you have by the following command: “cat /proc/cpuinfo | grep “model name” | wc -l“, so for example if you have 8 cores, then a value of 5.6 (70%) is the max. accepted value, where you should start getting worried afterwards.

As a rule: “The “100% utilization” mark is 1.00 on a single-core system, 2.00, on a dual-core, 4.00 on a quad-core, etc.”, and you can start worrying above the 70% utilization.

Source: http://blog.scoutapp.com/articles/2009/07/31/understanding-load-averages