Adaptive History-Based Memory Schedulers

As memory performance becomes increasingly important to overall system performance, the need to carefully schedule memory operations also increases. This paper presents a new approach to memory scheduling that considers the history of recently scheduled operations. This history-based approach provides two conceptual advantages: (1) it allows the scheduler to better reason about the delays associated with its scheduling decisions, and (2) it allows the scheduler to select operations so that they match the program's mixture of Reads and Writes, thereby avoiding certain bottlenecks within the memory controller. We evaluate our solution using a cycle-accurate simulator for the recently announced IBM Power5. When compared with an in-order scheduler, our solution achieves IPC improvements of 10.9% on the NAS benchmarks and 63% on the data-intensive Stream benchmarks. Using microbenchmarks, we illustrate the growing importance of memory scheduling in the context of CMP's, hardware controlled prefetching, and faster CPU speeds.