Towards A Portable Hierarchical View of Distributed Shared Memory Systems: Challenges and Solutions Millad Ghane Sunita Chandrasekaran Margaret S. Cheung Department of Computer Science Department of Computer and Information Physics Department University of Houston Sciences University of Houston TX, USA University of Delaware Center for Theoretical Biological Physics,
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[email protected] Abstract 1 Introduction An ever-growing diversity in the architecture of modern super- Heterogeneity has become increasingly prevalent in the recent computers has led to challenges in developing scientifc software. years given its promising role in tackling energy and power con- Utilizing heterogeneous and disruptive architectures (e.g., of-chip sumption crisis of high-performance computing (HPC) systems [15, and, in the near future, on-chip accelerators) has increased the soft- 20]. Dennard scaling [14] has instigated the adaptation of heteroge- ware complexity and worsened its maintainability. To that end, we neous architectures in the design of supercomputers and clusters need a productive software ecosystem that improves the usability by the HPC community. The July 2019 TOP500 [36] report shows and portability of applications for such systems while allowing how 126 systems in the list are heterogeneous systems confgured every parallelism opportunity to be exploited. with one or many GPUs. This is the prevailing trend in current gen- In this paper, we outline several challenges that we encountered eration of supercomputers. As an example, Summit [31], the fastest in the implementation of Gecko, a hierarchical model for distributed supercomputer according to the Top500 list (June 2019) [36], has shared memory architectures, using a directive-based program- two IBM POWER9 processors and six NVIDIA Volta V100 GPUs.