Enhancing Performance Portability of MPI Applications through Annotation-Based Transformations

MPI is the de facto standard for portable parallel programming on high-end systems. However, while the MPI standard provides functional portability, it does not provide sufficient performance portability across platforms. We present a framework that enables users to provide hints about communication patterns used within MPI applications. These annotations are then used by an automated program transformation system to leverage different MPI operations that better match each system´s capabilities. Our framework currently supports three automated transformations: coalescing of operations in MPI one-sided communications, transformation of blocking communications to nonblocking, which enables communication-computation overlap, and selection of the appropriate communication operators based on the cache-coherence support of the underlying platform. We use our annotation-based approach to optimize several benchmark kernels, and we demonstrate that the framework is effective at automatically improving performance portability for MPI applications.