Off-chip prefetching based on Hidden Markov Model for non-volatile memory architectures

• Published in: PloS one Vol. 16; no. 9; p. e0257047
• Main Authors: Lamela, Adrián, Ossorio, Óscar G, Vinuesa, Guillermo, Sahelices, Benjamín
• Format: Journal Article
• Language: English
• Published: San Francisco Public Library of Science 14.09.2021; Public Library of Science (PLoS)
• Subjects: Algorithms; Analysis; Bandwidths; Chips (memory devices); Clustering; Complexity; Computer and Information Sciences; Computer applications; Computer architecture; Computer memory; Computer science; Dynamic cell; Dynamic random access memory; Efficiency; Engineering; Engineering and Technology; Informatics; Latency; Markov chains; Markov processes; Microprocessors; Normal distribution; Physical sciences; Research and Analysis Methods; Simulation; Technology; Spain
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0257047

Non-volatile memory technology is now available in commodity hardware. This technology can be used as a backup memory for an external dram cache memory without needing to modify the software. However, the higher read and write latencies of non-volatile memory may exacerbate the memory wall problem. In this work we present a novel off-chip prefetch technique based on a Hidden Markov Model that specifically deals with the latency problem caused by complexity of off-chip memory access patterns. Firstly, we present a thorough analysis of off-chip memory access patterns to identify its complexity in multicore processors. Based on this study, we propose a prefetching module located in the llc which uses two small tables, and where the computational complexity of which is linear with the number of computing threads. Our Markov-based technique is able to keep track and make clustering of several simultaneous groups of memory accesses coming from multiple simultaneous threads in a multicore processor. It can quickly identify complex address groups and trigger prefetch with very high accuracy. Our simulations show an improvement of up to 76% in the hit ratio of an off-chip dram cache for multicore architecture over the conventional prefetch technique (g/dc). Also, the overhead of prefetch requests (failed prefetches) is reduced by 48% in single core simulations and by 83% in multicore simulations.