The present paper introduces the XcalableACC (XACC) programming model, which is a hybrid model of the XcalableMP (XMP) Partitioned Global Address Space (PGAS) language and OpenACC. XACC defines directives that enable programmers to mix XMP and OpenACC directives in order to develop applications that can use accelerator clusters with ease. Moreover, in order to improve the performance of stencil applications, the Omni XACC compiler provides functions that can transfer a halo region on accelerator memory via Tightly Coupled Accelerators (TCA), which is a proprietary network for transferring data directly among accelerators. In the present paper, we evaluate the productivity and the performance of XACC through implementations of the HIMENO Benchmark. The results show that thanks to the productivity improvements, XACC requires less than half the source lines of code compare to a combination of Message Passing Interface (MPI) and OpenACC, which is commonly used together as a typical programming model. As a result of these performance improvements, XACC using TCA achieved up to 2.7 times faster performance than could be obtained via the combination of OpenACC and MPI programming model using GPUDirect RDMA over InfiniBand.
An MPMD programming model is widely used as a master-worker program or a coupling program for multiple physical models. To utilize recent high-end parallel computers having more than several thousand nodes, we propose the communication library MPMPI between different multiple sets of MPI processes in the MPMD model. In particular, we present MPMPI interfaces that include interfaces for a PGAS language and the basic performance of MPMPI functions. As benchmark programs of the MPMPI library, we evaluated the performance of a master-worker program and a weak coupling program. As a result, we found that Pack/Unpack has a large influence on the performance of MPMPI functions, the interface of MPMPI functions can easily be used in these benchmark programs written in XcalableMP PGAS language, and the performances of the master-worker and weak coupling benchmark programs using the basic MPMPI functions are practical under the conditions of this paper.
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