Abstract: Advances in Gyrokinetic Particle in Cell Simulation for Fusion Plasmas to Extreme Scale

The Gyrokinetic Particle-in-cell (PIC) method has been successfully applied in studies of low-frequency microturbulence in magnetic fusion plasmas. While the excellent scaling of PIC codes on modern computing platforms is well established, significant challenges remain in achieving high on-chip concurrency for the new path to exascale systems. In addressing associated issues, it is necessary to deal with the basic gather-scatter operation and the relatively low computational intensity in the PIC method. Significant advancements have been achieved in optimizing gather-scatter operations in the gyrokinetic PIC method for next-generation multi-core CPU and GPU architectures. In particular, we will report on new techniques that improve locality, reduce memory conflict, and efficiently utilize shared memory on GPU's. Performance benchmarks on two high-end computing platforms -- the IBM BlueGene/Q (Mira) system at the Argonne Leadership Computing Facility (ALCF) and the Cray XK6 (Titan Dev) with the latest GPU at Oak Ridge Leadership Computing Facility (OLCF) - will be presented.