The Performance Monitoring Facility
Performance Monitoring Is Not Architecturally Defined
Whether or not a processor implements a Performance Monitoring facility and, if so, the method of implementation is design-specific. The facility is not part of the IA32 processor architecture spec. The manner in which it has been implemented on the Pentium®, P6 and Pentium® 4 processor families are not compatible with each other.
The author had a considerable amount of trouble achieving a detailed understanding of every aspect of this feature. The Intel® documentation of this feature is somewhat confusing in some areas.
The Pentium® and P6 processor families implemented two Performance Counters, permitting the simultaneously measurement ...