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PAPI is a widely used portable library for accessing hardware counters on modern microprocessors. PAPI offers both counting and sampling interfaces, but the sampling interface is extremely limited, consisting of a simple interrupt-driven interface that can periodically report processor state. In the past few years, the hardware and operating systems of modern processors have added support for new more advanced sampling features. These features enable information about non-uniform memory access (NUMA) behavior to be obtained. Currently, performance tool developers who want to provide sampling data to their users must make use of a complex low-level kernel interface, sometimes developing their own kernel patch to access the features they need. This paper reports on initial efforts to develop a middleware layer that will serve as a stable interface and enable tool developers to access sampling data through standard PAPI calls and to obtain data important for NUMA analysis.
