Hardware performance counter

In computers, hardware performance counters, or hardware counters are a set of special-purpose registers built into modern microprocessors to store the counts of hardware-related activities within computer systems. Advanced users often rely on those counters to conduct low-level performance analysis or tuning. In computers, hardware performance counters, or hardware counters are a set of special-purpose registers built into modern microprocessors to store the counts of hardware-related activities within computer systems. Advanced users often rely on those counters to conduct low-level performance analysis or tuning. The number of available hardware counters in a processor is limited while each CPU model might have a lot of different events that a developer might like to measure. Each counter can be programmed with the index of an event type to be monitored, like a L1 cache miss or a branch misprediction. One of the first processors to implement such counter and an associated instruction RDPMC to access it was the Intel Pentium, but they were not documented until Terje Mathisen wrote an article about reverse engineering them in Byte July 1994.