Hybridizing S3D into an exascale application using OpenACC: An approach for moving to multi-petaflops and beyond

Hybridization is the process of converting an application with a single level of parallelism to an application with multiple levels of parallelism. Over the past 15 years a majority of the applications that run on High Performance Computing systems have employed MPI for all of the parallelism within the application. In the Peta-Exascale computing regime, effective utilization of the hardware requires multiple levels of parallelism matched to the macro architecture of the system to achieve good performance. A hybridized code base is performance portable when sufficient parallelism is expressed in an architecture agnostic form to achieve good performance on a range of available systems. The hybridized S3D code is performance portable across today's leading many core and GPU accelerated systems. The OpenACC framework allows a unified code base to be deployed for either (Manycore CPU or Manycore CPU+GPU) while permitting architecture specific optimizations to expose new dimensions of parallelism to be utilized.