Talk for MacIT 2014. This talk is about systems performance on OS X, and introduces the USE Method to check for common performance bottlenecks and errors. This methodology can be used by beginners and experts alike, and begins by constructing a checklist of the questions we’d like to ask of the system, before reaching for tools to answer them. The focus is resources: CPUs, GPUs, memory capacity, network interfaces, storage devices, controllers, interconnects, as well as some software resources such as mutex locks. These areas are investigated by a wide variety of tools, including vm_stat, iostat, netstat, top, latency, the DTrace scripts in /usr/bin (which were written by Brendan), custom DTrace scripts, Instruments, and more. This is a tour of the tools needed to solve our performance needs, rather than understanding tools just because they exist. This talk will make you aware of many areas of OS X that you can investigate, which will be especially useful for the time when you need to get to the bottom of a performance issue.