Accelerating BFS via Data Structure-Aware Prefetching on GPU

Breadth First Search (BFS) is a key graph traversing algorithm for many graph analytics applications. In recent decades, as the scale of the graph analytics problem has become larger and larger, it has raised many interests to accelerate graph traversing on GPU. However, due to the irregular memory access pattern of BFS, a great number of the memory divergent accesses harm the efficiency of GPU dramatically. Data prefetching can fetch useful data into the on-chip memory in advance to reduce the latency of accessing the off-chip memory. However, traditional prefetching techniques on GPU cannot deal with irregular memory accesses efficiently. By analyzing BFS algorithms for GPU, we find an opportunity to design an efficient prefetching mechanism by using the explicit information of the graph data structure. In this paper, we propose DSAP, a data structure-aware prefetcher on GPU that generates prefetching requests based on the well-defined data structure access pattern of BFS. Also, we introduce an adaptive fine-grain prefetching management to adjust the status of the prefetching granularity dynamically to balance the cache resource contention and data prefetching based on the utilization of the prefetched data. We implement DSAP on a GPGPU-sim simulator and evaluate six data sets from three different kinds of applications. DSAP can achieve a geometrical mean IPC improvement of 28%, up to 48.4%, compared with that of GPU with no prefetching technique, while in contrast, a stride-based global history buffer prefetching mechanism makes no effects on improving BFS performance for these data sets. Also, we use the GPUWattch to estimate the power consumption, and the power increases 8.3% in average and up to 11.8%, but the total energy cost drops 15.1% in average.