Optimizing MapReduce for GPUs with effective shared memory usage

Accelerators and heterogeneous architectures in general, and GPUs in particular, have recently emerged as major players in high performance computing. For many classes of applications, MapReduce has emerged as the framework for easing parallel programming and improving programmer productivity. There have already been several efforts on implementing MapReduce on GPUs. In this paper, we propose a new implementation of MapReduce for GPUs, which is very effective in utilizing shared memory, a small programmable cache on modern GPUs. The main idea is to use a reduction-based method to execute a MapReduce application. The reduction-based method allows us to carry out reductions in shared memory. To support a general and efficient implementation, we support the following features: a memory hierarchy for maintaining the reduction object, a multi-group scheme in shared memory to trade-off space requirements and locking overheads, a general and efficient data structure for the reduction object, and an efficient swapping mechanism. We have evaluated our framework with seven commonly used MapReduce applications and compared it with the sequential implementations, MapCG, a recent MapReduce implementation on GPUs, and Ji et al.'s work, a recent MapReduce implementation that utilizes shared memory in a different way. The main observations from our experimental results are as follows. For four of the seven applications that can be considered as reduction-intensive applications, our framework has a speedup of between 5 and 200 over MapCG (for large datasets). Similarly, we achieved a speedup of between 2 and 60 over Ji et al.'s work.