京におけるジャイロ運動論的シミュレーションコードGKVの超並列スペクトル計算

Massively-parallelized spectral calculations of the gyrokinetic simulation code GKV on the K computer

前山 伸也; 渡邉 智彦*; 井戸村 泰宏   ; 仲田 資季; 沼波 政倫*; 石澤 明宏*

Maeyama, Shinya; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki; Nunami, Masanori*; Ishizawa, Akihiro*

To analyze multi-scale plasma turbulence in magnetically confined plasma, we have extended the gyrokinetic Vlasov simulation code GKV to run efficiently on the K computer. A key numerical technique is the speed up of the parallel two-dimensional (2D) Fast Fourier Transform (FFT) algorithms. MPI/OpenMP hybrid parallelization with 4D domain decomposition is newly implemented to use a large number of cores. Perpendicular dynamics is solved by using the spectral method with 2D FFTs, where the data transpose often degrades scalability. The MPI process mapping is optimized for the 3D torus inter-node network on the K computer, so that the transpose communications are performed among the neighboring nodes located in a 3D box shape. Additionally, overlaps of FFTs and data transpose are implemented by using OpenMP directives. Thanks to the developed methods, GKV achieves almost linear speed-up beyond 100k cores with high parallel efficiency about 99.9998 per cent.