user manual

22007E/0—November 1999 AMD Athlon™ Processor x86 Code Optimization
Overview 161
Appendix D
Performance-Monitoring
Counters
This chapter describes how to use the AMD Athlon™ processor
performance monitoring counters.
Overview
The AMD Athlon processor provides four 48-bit performance
counters, which allows four types of events to be monitored
simultaneously. These counters can either count events or
measure duration. When counting events, a counter is
incremented each time a specified event takes place or a
specified number of events takes place. When measuring
duration, a counter counts the number of processor clocks that
occur while a specified condition is true. The counters can
count events or measure durations that occur at any privilege
level. Table 11 on page 164 lists the events that can be counted
with the performance monitoring counters.
Performance Counter Usage
The performance monitoring counters are supported by eight
MSRs—PerfEvtSel[3:0] are the performance event select
MSRs, and PerfCtr[3:0] are the performance counter MSRs.