Have a look at "Black Belt Itanium 2 Processor Performance: Performance Monitoring Capabilities" (http://www.intel.com/cd/ids/developer/asmo-na/eng/microprocessors/itanium/195488.htm). This is the second in a series of five articles by David Levinthal on Itanium 2 programming issues. There is also a link in this paper to the "Intel Itanium 2 Processor Reference Manual for Software Developement and Optimization".