Balancing CPU-GPU Collaborative High-order CFD Simulations on the Tianhe-1A Supercomputer

HOSTA is an in-house high-order CFD software that can simulate complex flows with complex geometries. Large-scale high-order CFD simulations using HOSTA require massive HPC resources, thus motivating us to port it onto modern GPU-accelerated supercomputers like Tianhe-1A. To achieve a greater speedup and fully tap the potential of Tianhe-1A, we collaborate CPU and GPU for HOSTA instead of using a naive GPU-only approach. We present multiple novel techniques to balance the loads between the store-poor GPU and the store-rich CPU, and overlap the collaborative computation and communication as far as possible. Taking CPU and GPU load balance into account, we improve the maximum simulation problem size per Tianhe-1A node for HOSTA by 2.3X, meanwhile the collaborative approach can improve the performance by around 45% compared to the GPU-only approach. Scalability tests show that HOSTA can achieve a parallel efficiency of above 60% on 1024 Tianhe-1A nodes. With our method, we have successfully simulated China's large civil airplane configuration C919 containing 150M grid cells. To our best knowledge, this is the first paper that reports a CPU-GPU collaborative high-order accurate aerodynamic simulation result with such a complex grid geometry.