This is a summary / cheat-sheet for diagnosing performance problems with the "USE" method. It's explained in much more detail here: http://www.brendangregg.com/usemethod.html

Worth checking out the rest of the site too, really useful stuff for performance engineers.

For reference, the definitions are:

* utilization: the average time that the resource was busy servicing work

* saturation: the degree to which the resource has extra work which it can't service, often queued

* errors: the count of error events