Cache-Conscious Wavefront Scheduling

This paper studies the effects of hardware thread scheduling on cache management in GPUs. We propose Cache-Conscious Wave front Scheduling (CCWS), an adaptive hardware mechanism that makes use of a novel intra-wave front locality detector to capture locality that is lost by other schedulers due to excessive contention for cache capacity. In contrast to improvements in the replacement policy that can better tolerate difficult access patterns, CCWS shapes the access pattern to avoid thrashing the shared L1. We show that CCWS can outperform any replacement scheme by evaluating against the Belady-optimal policy. Our evaluation demonstrates that cache efficiency and preservation of intra-wave front locality become more important as GPU computing expands beyond use in high performance computing. At an estimated cost of 0.17% total chip area, CCWS reduces the number of threads actively issued on a core when appropriate. This leads to an average 25% fewer L1 data cache misses which results in a harmonic mean 24% performance improvement over previously proposed scheduling policies across a diverse selection of cache-sensitive workloads.