Development of communication overlap techniques in 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*

Five dimensional gyrokinetic simulations are standard approaches in analyzing turbulent transport phenomena in fusion plasmas. For the purpose of analyzing fusture large devices such as the ITER, an extention of simulation capabilities, in particular, in the device size, is important, and larger computational resources are needed. However, a severe technical requirement on extreme parallelizm beyond 100k cores is required to extract computing power from present Peta-scale and future Exa-scale machines. In this work, we develop novel communication overlap techniques on finite difference plasma turbulence code GT5D, and achieve a good strong scaling up to 200k cores with an order of magnitude higher parallel efficiency of 99.9998% on the K computer.