Implementing Lattice QCD Application with XcalableACC Language on Accelerated Cluster

Accelerated clusters, which are distributed memory systems equipped with accelerators, have been used in various fields. For accelerated clusters, programmers often implement their applications by a combination of MPI and CUDA (MPI+CUDA). However, the approach faces programming complexity issues. This paper introduces the XcalableACC (XACC) language, which is a hybrid model of XcalableMP (XMP) and OpenACC. While XMP is a directive-based language for distributed memory systems, OpenACC is also a directive-based language for accelerators. XACC enables programmers to develop applications on accelerated clusters with ease. To evaluate XACC performance and productivity levels, we implemented a lattice quantum chromodynamics (Lattice QCD) application using XACC on 64 compute nodes and 256 GPUs and found its performance was almost the same as that of MPI+CUDA. Moreover, we found that XACC requires much less change from the serial Lattice QCD code than MPI+CUDA to implement the parallel Lattice QCD code.