An Efficient Implementation of Stencil Communication for the XcalableMP PGAS Parallel Programming Language

Partitioned Global Address Space (PGAS) programming languages have emerged as a means by which to program parallel computers, which are becoming larger and more complicated. For such languages, regular stencil codes are still one of the most important goals. We implemented three methods of stencil communication in a compiler for a PGAS language XcalableMP, which are 1) based on derived-datatype messaging; 2) based on packing/unpacking, which is especially effective in multicore environments; and 3) experimental and based on one-sided communication on the K computer, where the RDMA function suitable for one-sided communication is available. We evaluated their performances on the K computer. As a result, we found that the first and second methods are effective under different conditions, and selecting either of these methods at runtime would be practical. We also found that the third method is promising but that the method of synchronization is a remaining problem for higher performance.