HBM-Resident Prefetching for Heterogeneous Memory System

To meet the increasing demands for very large memory capacities, bandwidth and energy efficiency, researchers are exploring the use of heterogeneous memory systems that combine faster 3D-DRAMs, DDRx DRAM and non-volatile memories (NVMs). In this paper we evaluate prefetching in a flat-addressable heterogeneous memory comprising High Bandwidth Memory (HBM) and phase change memory (PCM). We find that large prefetch buffers (64 MB) can outperform smaller buffer sizes (2 MB), however it is not feasible to place such large buffers on the processor die. Hence, in this paper we evaluate an HBM-resident prefetch buffer that provides larger capacity and takes advantage of HBM’s higher memory bandwidth. We also present new prefetching policies that accommodate the differences in data path as compared to traditional prefetchers. We show that, reserving a small fraction (1/16th) of HBM memory to host a hardware prefetch buffer can improve IPC for a set of SPEC CPU2006 and HPC benchmarks by an average of 34% and a maximum of 98% over a baseline system with no-prefetching. Prefetching reduces total PCM traffic by 10% on average, which results in more memory traffic to the faster HBM, providing overall performance improvement. We found that such prfetching outperforms CAMEO and Alloy cache schemes on average by 60% and 10%, respectively.