Design and Preliminary Evaluation of Omni OpenACC Compiler for Massive MIMD Processor PEZY-SC.

PEZY-SC is a novel massive Multiple Instruction Multiple Data (MIMD) processor used as an accelerator and characterized by high power efficiency. OpenACC is a standard directive-based programming model for accelerators, and programmers can concisely offload data and computation to the accelerators. In this paper, we present the design and preliminary implementation of an OpenACC compiler for a PEZY-SC. Our compiler translates C code with OpenACC directives to the corresponding PZCL code, which is the programming environment for PEZY-SC. The evaluation shows that the performance of the OpenACC version achieves over 98% at N-body and up to 88% at NAS Parallel Benchmarks CG than that of the PZCL version. In addition, we examined optimization techniques such as kernel merging and explicit context switching to exploit the PEZY-SC MIMD architecture, which differs from the single instruction multiple data graphics processing units. We found these optimizations useful in improving the performance and will be implemented in the future release.