A Burst Scheduling Access Reordering Mechanism

Utilizing the nonuniform latencies of SDRAM devices, access reordering mechanisms alter the sequence of main memory access streams to reduce the observed access latency. Using a revised M5 simulator with an accurate SDRAM module, the burst scheduling access reordering mechanism is proposed and compared to conventional in order memory scheduling as well as existing academic and industrial access reordering mechanisms. With burst scheduling, memory accesses to the same rows of the same banks are clustered into bursts to maximize bus utilization of the SDRAM device. Subject to a static threshold, memory reads are allowed to preempt ongoing writes for reduced read latency, while qualified writes are piggybacked at the end of bursts to exploit row locality in writes and prevent write queue saturation. Performance improvements contributed by read preemption and write piggybacking are identified. Simulation results show that burst scheduling reduces the average execution time of selected SPEC CPU2000 benchmarks by 21% over conventional bank in order memory scheduling. Burst scheduling also outperforms Intel's patented out of order memory scheduling and the row hit access reordering mechanism by 11% and 6% respectively