Analytical Study on Bandwidth Efficiency of Heterogeneous Memory Systems

Abstract

Heterogeneous memory systems integrate different memory technologies to balance design requirements such as bandwidth, capacity, and cost. Performance of these systems depends heavily on memory hierarchy organization, memory attributes, and application characteristics. In this paper, we present analytical bandwidth models for a range of heterogeneous memory systems composed of DRAM and non-volatile memory (NVM). Our models enable exploring heterogeneous memory systems with different organizations and attributes. Using the models, we study the bandwidth efficiency of heterogeneous memory systems to provide insights into the bandwidth bottlenecks of these systems under different application characteristics. Our analytical results highlight the importance of NVM read-write bandwidth asymmetry and DRAM-NVM bandwidth asymmetry in bandwidth efficiency. Specifically, in flat non-uniform memory access (NUMA) systems, the read bandwidth is maximized when a certain portion of bandwidth is delivered by DRAM and that portion depends on multiple factors including DRAM and NVM bandwidth attributes and application bandwidth characteristics. In DRAM-cache-based systems, when the hit rate is low, the impact of the DRAM cache organization on the read bandwidth is minimal. However, at higher hit rates and NVM bandwidths, the impact of the cache organization on sustained read bandwidth becomes pronounced.