Reducing Communication Overhead in Multi-GPU Hybrid Solver for 2D Laplace's Equation

The possibility of porting algorithms to graphics processing units (GPUs) raises significant interest among researchers. The natural next step is to employ multiple GPUs, but communication overhead may limit further performance improvement. In this paper, we investigate techniques reducing overhead on hybrid CPU-GPU platforms, including careful data layout and usage of GPU memory spaces, and use of non-blocking communication. In addition, we propose an accurate automatic load balancing technique for heterogeneous environments. We validate our approach on a hybrid Jacobi solver for 2D Laplace's Equation. Experiments carried out using various graphics hardware and types of connectivity have confirmed that the proposed data layout allows our fastest CUDA kernels to reach the analytical limit for memory bandwidth (up to 106 GB/s on NVidia GTX 480), and that the non-blocking communication significantly reduces overhead, allowing for almost linear speed-up, even when communication is carried out over relatively slow networks.