Optimizations of the gyrokinetic Vlasov simulation code GKV for the K computer

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の最適化

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*

We report the optimizations of the gyrokinetic Vlasov simulation code GKV, which performs five-dimensional computational fluid dynamics calculations by using spectral and finite difference methods, for the K computer. First, the segmented rank mapping on the three-dimensional torus network is advantageous to utilize the bi-section bandwidth and to avoid collisions of the messages, and, therefore, to reduce communication costs. Second, the uses of the collective communication algorithm optimized for the K computer and of the simultaneous communications on the Tofu interconnect further reduce the communication costs. Finally, computation-communication overlaps with pipelining methods effectively mask the communication cost. The highly-optimized code improves strong scaling up to 600 k cores (with the parallel efficiency 99.99994%), and demonstrates its applicability and efficiency for the peta-scale computing.