Development of numerical techniques toward extreme scale fusion plasma turbulence simulations

Idomura, Yasuhiro   ; Nakata, Motoki; Yamada, Susumu  ; Machida, Masahiko  ; Imamura, Toshiyuki*; Watanabe, Tomohiko*; Nunami, Masanori*; Inoue, Hikaru*; Tsutsumi, Shigenobu*; Miyoshi, Ikuo*; Shida, Naoyuki*

A plasma turbulence research based on 5D gyrokinetic simulations is one of the most critical and demanding issues in fusion science. To pioneer new physics regimes both in problem sizes and in time scales, an improvement of strong scaling is essential. Overlap of computations and communications is a promising approach to improve strong scaling, but it often fails on practical applications with conventional MPI libraries. In this work, this classical issue is clarified, and resolved by developing communication overlap techniques with mpi_test and communication threads, which work even on conventional MPI libraries and network hardwares. These techniques dramatically improve the parallel efficiency of a gyrokinetic Eularian code GT5D on K and Helios, which adopt dedicated and commodity networks.