Modern General-Purpose computation on Graphics Processing Units (GPGPUs) explore parallelism in applications by building massively parallel architecture and apply multithreading technology to hide the instruction and memory latencies. Such architectures become increasingly popular for parallel applications using CUDA/OpenCL programming languages. In this paper, we investigate thread scheduling algorithms on such highly-threaded GPGPUs. The traditional round-robin scheduling schemes are inefficient in handling instruction execution and memory accesses with disparate latencies. We introduce a new GPGPU thread (warp) scheduling algorithm which enables flexible round-robin distance for efficiently utilizing multithread parallelism and use program-guided priority shift among concurrent threads (warps) to allow more overlaps between short-latency compute instructions and long-latency memory accesses. Performance evaluations demonstrate that the new scheduling algorithm improves a set of kernel execution times by an average of 12% with 52% reduction on scheduler stall cycles over the fine-granularity round-robin scheme. In this paper, we also accomplish a thorough evaluation of various thread scheduling algorithms based on the amount of hardware threads, the scheduling overhead, and the global memory latency.
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