A characterization of shared data access patterns in UPC programs

The main attraction of Partitioned Global Address Space (PGAS) languages to programmers is the ability to distribute the data to exploit the affinity of threads within shared-memory domains. Thus, PGAS languages, such as Unified Parallel C (UPC), are a promising programming paradigm for emerging parallel machines that employ hierarchical data- and task-parallelism. For example, large systems are built as distributed-shared memory architectures, where multicore nodes access a local, coherent address space and many such nodes are interconnected in a non-coherent address space to form a high-performance system. This paper studies the access patterns of shared data in UPC programs. By analyzing the access patterns of shared data in UPC we are able to make three major observations about the characteristics of programs written in a PGAS programming model: (i) there is strong evidence to support the development of automatic identification and automatic privatization of local shared data accesses; (ii) the ability for the programmer to specify how shared data is distributed among the executing threads can result in significant performance improvements; (iii) running UPC programs on a hybrid architecture will significantly increase the opportunities for automatic privatization of local shared data accesses.