Graph parallel actor language --- a programming language for parallel graph algorithms

We introduce a domain-specific language, GRAph PArallel Actor Language, that enables parallel graph algorithms to be written in a natural, high-level form. GRAPAL is based on our GraphStep compute model, which enables a wide range of parallel graph algorithms that are high-level, deterministic, free from race conditions, and free from deadlock. Programs written in GRAPAL are easy for a compiler and runtime to map to efficient parallel field programmable gate array (FPGA) implementations. We show that the GRAPAL compiler can verify that the structure of operations conforms to the GraphStep model. We allocate many small processing elements in each FPGA that take advantage of the high on-chip memory bandwidth (5x the sequential processor) and process one graph edge per clock cycle per processing element. We show how to automatically choose parameters for the logic architecture so the high-level GRAPAL programming model is independent of the target FPGA architecture. We compare our GRAPAL applications mapped to a platform with four 65 nm Virtex-5 SX95T FPGAs to sequential programs run on a single 65 nm Xeon 5160. Our implementation achieves a total mean speedup of 8x with a maximum speedup of 28x. The speedup per chip is 2x with a maximum of 7x. The ratio of energy used by our GRAPAL implementation over the sequential implementation has a mean of 1/10 with a minimum of 1/80.