Hardware support for address mapping in PGAS languages: a UPC case study

The Partitioned Global Address Space (PGAS) programming model strikes a balance between the explicit, locality-aware, message-passing model and locality-agnostic, but easy-to-use, shared memory model (e.g. OpenMP). However, the PGAS memory model comes at a performance cost which limits both scalability and performance. Compiler optimizations are often not sufficient and manual optimizations are needed which considerably limit the productivity advantage. This paper proposes a hardware architectural support for PGAS, which allows the processor to efficiently handle shared addresses through new instructions. A prototype compiler is realized allowing to use the support with unmodified code, preserving the PGAS productivity advantage. Speedups of up to 5.5x are demonstrated on the unmodified NAS Parallel Benchmarks using the Gem5 full system simulator.