This paper proposes a portable performance interface for OpenMP to aid in the integration of performance tools in OpenMP programming environments. Defined as a library API, the interface exposes OpenMP execution events of interest (e.g., sequential, parallel, and synchronization events) for performance observation, and passes OpenMP context descriptors to inform the performance interface library of region-specific information. Because OpenMP uses compiler directives (pragmas) to express shared memory parallelism, our definition of the performance tool API must be consistent with the operational semantics of the directives. To show how this is accomplished, we describe how the API is used in rewriting OpenMP directives in functionally equivalent, but source-instrumented forms. The OPARI tool can perform this OpenMP directive rewriting automatically, inserting pomp performance calls where appropriate.
The benefits of the proposed performance interface are several. First, it gives a performance API target for source-to-source instrumentation tools (e.g., OPARI), allowing for instrumented OpenMP codes that are portable across compilers and machine platforms. Second, the performance library interface provides a target for tool developers to port performance measurement systems. This enables multiple performance tools to be used in OpenMP performance analysis. We show how EXPERT and TAU are integrated by redefining the pomp calls. Third, the API also offers a target for OpenMP compilers to generate pomp calls that can both access internal, compiler-specific performance libraries and external performance packages. Finally, if the OpenMP community could adopt an OpenMP performance interface such as the one we proposed, it would significantly improve the integration and compatibility between compilers and performance tools, and, perhaps more importantly, the portability of performance analysis techniques.
In the future, we hope to work with the OpenMP standards organization to promote the definition for a performance tool API, offering our proposal here for consideration. We will enhance the OPARI source-to-source instrumentation approach with support for user function instrumentation using PDT [12]. Other opportunities are also possible with the integration of the API in OpenMP compilers and the use of other performance technologies for instrumentation and measurement. We hope to work with KAI and Pallas to investigate the use of our proposed performance tool interface in the KAP/Pro Guide compiler with Vampirtrace as the basis for the pomp performance library implementation.