High Performance Gravitational N-body Simulations on Supercomputer Fugaku.

We report performance results of large astrophysical N-body simulations on supercomputer Fugaku. We use the hybrid TreePM algorithm, in which the short-range force is evaluated by the oct-tree method, and the long-range force is solved by the particle-mesh method. We introduce three innovations that significantly improve the performance on the novel CPU and extremely large system: the near-ultimate optimization of gravity kernel for short-range forces, the domain decomposition with accelerated communications in hardware-oriented ways, and a novel communication algorithm for long-range forces. We demonstrate that our code scales near linearly up to 158,976 nodes (7,630,848 CPU cores) of Fugaku and enables us to integrate about 1.45 trillion particles per second, which is the world fastest time-to-solution. The average performance achieved is 95.82 Pflops, which corresponds to ∼ 10% of the peak in single precision.