I like using this to profile JRuby code, though it took me a while to get the hang of things and extract useful information. NetBeans IDE for Java includes a Java profiler. Walks through the steps of configuring NetBeans, launching JRuby with profiling settings, connecting NetBeans to JRuby, and analyzing the results. A case study and tutorial on using the NetBeans profiler to profile Ruby code running on the JVM via JRuby.
