Adaptive Row Addressing for Cost-Efficient Parallel Memory Protocols in Large-Capacity Memories

Abstract

Modern commercial workloads drive a continuous demand for larger and still low-latency main memories. JEDEC member companies indicate that parallel memory protocols will remain key to such memories, though widening the bus (increasing the pin count) to address larger capacities would cause multiple issues ultimately reducing the speed (the peak data rate) and cost-efficiency of the protocols. Thus to stay high-speed and cost-efficient, parallel memory protocols should address larger capacities using the available number of pins. This is accomplished by multiplexing the pins to transfer each address in multiple bus cycles, implementing Multi-Cycle Addressing (MCA). However, additional address-transfer cycles can significantly worsen performance and energy efficiency. This paper contributes with the concept of adaptive row addressing that comprises row-address caching to reduce the number of address-transfer cycles, enhanced by row-address prefetching and an adaptive row-access priority policy to improve state-of-the-art memory schedulers. For a case-study MCA protocol, the paper shows that the proposed concept improves: i) the read latency by 7.5% on average and up to 12.5%, and ii) the system-level performance and energy efficiency by 5.5% on average and up to 6.5%. This way, adaptive row addressing makes the MCA protocol as efficient as an idealistic protocol of the same speed but with enough pins to transfer each row address in a single bus cycle.