Comment 83 for bug 888039

Michael, to find the cause of high CPU usage you need a profiler, not a debugger.

Most profilers need special code compiled in to your application, but Valgrind has a plugin Callgrind that works with any existing binary (as do all valgrind plugins):
    http://valgrind.org/docs/manual/cl-manual.html

Callgrind will give you nice sorted lists of the functions using the highest CPU. It is not for beginners though. Maybe later I will write a HOWTO on profiling compiz with callgrind so more people can give it a go and provide some nice rich data on compiz performance.