The purpose of the PAPI project is to specify a standard API for accessing hardware performance counters available on most modern microprocessors. These counters exist as a small set of registers that count "events", which are occurrences of specific signals and states related to the processor's function. Monitoring these events facilitates correlation between the structure of source/object code and the efficiency of the mapping of that code to the underlying architecture. This correlation has a variety of uses in performance analysis and tuning. The PAPI project has proposed a standard set of hardware events and a standard cross-platform library interface to the underlying counter hardware. The PAPI library has been or is in the process of being implemented on all major HPC platforms. The PAPI project is developing end-user tools for dynamically selecting and displaying hardware counter performance data. PAPI support is also being incorporated into a number of third-party tools.

PrologueShor6ly after the collapse of Soviet domination in Eastern Europe, a Polish housewife was interviewed by Na6ional Public Radio.She complained that the introduction of free enterprise to Poland was a great inconvenience.Now, instead of shopping at the most conveniently located store, secure in the knowledge that prices were uniform, she had to go from store to store comparing prices, in order to be sure that she was making the best buy."Why should prices be different at each store?" she complained."After all, they are all selling the same things."On the surface, her remarks seem to make a great deal of sense.If we can find the fallacy in her thinking, we will learn a small lesson about a very important subject, free-market economics, and more relevantly, a big lesson about a less important subject, software reuse libraries.