Optimization of fusion plasma turbulence code GT5D on FUGAKU and SUMMIT

Idomura, Yasuhiro   ; Ali, Y.*; Ina, Takuya*; Imamura, Toshiyuki*

Implicit finite difference solvers based on Krylov subspace methods occupy dominant computing costs in the Gyrokinetic Toroidal 5D full-f Eulerian code GT5D. Under the post-K project, advanced communication avoiding (CA) Krylov subspace methods have been developed for exascale computing platforms, which have limited inter-node communication performance compared with accelerated computation. In this work, we develop a new mixed precision CA-GMRES solver using a FP16 preconditioner, which dramatically reduces the number of iterations, and thus, halo data communications. We port the new solver on FUGAKU and Summit, and compare its performance against conventional solvers on existing muti/many-core processors.