Evaluation of the Global Address Space Programming Interface (GASPI)

The first exascale supercomputers are expected by the end of this decade and will presumably feature an increase in core count, but a decrease in the amount of memory available per core. As of now, it is still unclear if the current programming models will provide high performance on exascale systems. One programming model considered to be an alternative to MPI is the so-called partitioned global address space (PGAS) model. Within this paper we evaluate a relatively new PGAS API: the Global Address Space Programming Interface (GASPI) and compare it to MPI on the basis of microbenchmarks. These benchmarks show that GASPI provides about the same level of performance for single-threaded communication, but is up to an order of magnitude faster than both Intel and IBM MPI for multi-threaded communication. Hereafter, we discuss the different features of GASPI in comparison to two main PGAS languages, namely UPC and CAF. In addition, we present a basic numerical algorithm, a dense matrix-matrix multiplication, as an example on how an implementation can make efficient use of GASPI's features, especially the asynchronous and one-sided communication mechanisms.