Articles to understanding the CPU load on a Linux box:

• Understanding Linux CPU Load – when should you be worried?
• Wikipedia – Load (computing)
• EVERYTHING YOU NEED TO KNOW ABOUT LINUX CPU LOAD
• How to interpret CPU load on Linux
• High System Load with Low CPU Utilization on Linux?

Tools:

• How do I find out Linux CPU utilization?

Some interesting commands:

• ps awwlx –sort=vsz: This shows processes sorted by virtual sizes (which doesinclude shared libraries, but also counts blocks swapped out to disc).
• watch -n1 “cat /proc/interrupts”: There are some times that hardware is the source of high load, and the reason would be that some peripherals generate a lot of interrupts (IRQ) that might end up locking the CPU until finished, this is hard to catch since tools to watch it are less used, on way to look at interrupts would be to do

Enjoy!!!