MySQL’s Performance schema is a relatively new tool for measuring performance and MySQL Workbecn 6.1.2 is the latest beta of that software. I have not had a lot of time to play with performance schema but now I am taking my first steps with the help of Workbench. Startup Workbench and you will find under the Navigator an item labeled Performance Schema Setup. Flip the toggle from OFF to ON and then start exploring.
Now you can run queries and see what the costs are, where the server is waiting, or what indexes remain unused. You can even use workbench to alter the options file to setup other Performance Schema instruments. Trying various settings for optimizer_search_depth is simple with the GUI.