Exploiting future Exascale systems with Partitioned Global Address Spaces

The high-performance computing (HPC) industry is determinedly building towards next-generation exascale supercomputers. With this big leap in performance, the number of cores present in these future systems will be immense. Current state-of-the-art bulk synchronous two-sided communication models might not provide the massive performance and scalability required to exploit the power of these future systems. A paradigm shift towards an asynchronous communication and execution model to support the increasing number of nodes present in future supercomputers seems to be unavoidable. GASPI (Global Address Space Programming Interface) offers a Partitioned Global Address Space (PGAS) and allows for zero-copy data transfers that are completely asynchronous and one-sided, enabling a true overlap of communication and computation. Although promising, the PGAS model is still immature. Industrial-level HPC applications have yet to be developed with this model, which generates uncertainty about the model’s effectiveness with real-world applications. The goal of this thesis is to contribute to a better understanding of the actual strengths and limitations of the GASPI programming model when applied to HPC applications that will benefit from future exascale systems. To achieve that, we focused on the parallelization of a representative method from the domain of plasma physics, the Particle-in-Cell (PIC) method. Departing from an existing sequential implementation (ZPIC), we evaluated the performance and programming productivity of GASPI when used to parallelize this implementation. After a thorough performance evaluation on the MareNostrum 4 supercomputer we concluded that, while GASPI might fall behind the industry standard in terms of usability, its performance and scalability reliably outperformed an MPI implementation of the same application.