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.