Abstract: Real-time performance monitoring facility in an integrated circuit (IC) data processor for monitoring events related to different bus activity. The monitoring facility is accessible via a bus connection the IC. Events include device acquisition and ownership time, and the number of requests and grants on a given bus. The events are counted as occurrences and durations by a number of event counters integrated in the IC. The IC can notify software when the counters overflow. The IC may feature multiple clock domains, including, for instance, multiple bus interfaces operating at different clock frequencies, in which events from different clock domains may be tracked by the same counter. In one embodiment, the performance monitoring facility is integrated into an I/O processor (IOP) die that complies with the popular intelligent I/O (I2O) and Peripheral Components Interconnect (PCI) specifications.