ALRESCHA: A Lightweight Reconfigurable Sparse-Computation Accelerator

Sparse problems that dominate a wide range of applications fail to effectively benefit from high memory bandwidth and concurrent computations in modern high-performance computer systems. Therefore, hardware accelerators have been proposed to capture a high degree of parallelism in sparse problems. However, the unexplored challenge for sparse problems is the limited opportunity for parallelism because of data dependencies, a common computation pattern in scientific sparse problems. Our key insight is to extract parallelism by mathematically transforming the computations into equivalent forms. The transformation breaks down the sparse kernels into a majority of independent parts and a minority of data-dependent ones and reorders these parts to gain performance. To implement the key insight, we propose a lightweight reconfigurable sparse-computation accelerator (Alrescha). To efficiently run the data-dependent and parallel parts and to enable fast switching between them, Alrescha makes two contributions. First, it implements a compute engine with a fixed compute unit for the parallel parts and a lightweight reconfigurable engine for the execution of the data-dependent parts. Second, Alrescha benefits from a locally-dense storage format, with the right order of non-zero values to yield the order of computations dictated by the transformation. The combination of the lightweight reconfigurable hardware and the storage format enables uninterrupted streaming from memory. Our simulation results show that compared to GPU, Alrescha achieves an average speedup of 15.6x for scientific sparse problems, and 8x for graph algorithms. Moreover, compared to GPU, Alrescha consumes 14x less energy.