LAMS: A latency-aware memory scheduling policy for modern DRAM systems

Abstract

This paper introduces a new memory scheduling policy called LAMS, which is inspired by a recently proposed memory architecture and targets for future high capacity memory systems. As memory capacity increases, the bit-lines connected to memory row buffers become much longer, dramatically lengthening memory access latency, due to increased parasitic capacitance. Recent study has proposed to partition long bit-lines into near and far (relative to the row buffer) segments via inserting isolation transistors such that access to near segment can be accomplished much faster, while access to far segment remains nearly the same. However, how to effectively leverage the new memory architecture still remains unexplored. We suggest to take advantage of this new memory architecture via performing latency-aware memory scheduling for pending requests to explore their performance potentials. In this scheduling policy, each memory request is classified to one of the following three categories, row-buffer hit, near-buffer, and far-buffer. Based on the classification, it issues requests in the order of row-buffer hit → near-buffer → far-buffer. In doing so, it avoids long-latency requests blocking short-latency memory requests, reducing total memory queuing time in the memory controller and improving overall memory performance. Our evaluation results on a simulated memory system show that comparing with the commonly used FR-FCFS scheduler, our LAMS improves performance and energy efficiency by up to 20.6% and 34%, respectively. Even comparing with the four competitive schedulers chosen from memory scheduling champion (MSC), LAMS still improves performance and energy efficiency by up to 6.1% and 23.4%, respectively.