Versatile refresh: Low complexity refresh scheduling for high-throughput multi-banked eDRAM

Mohammad Alizadeh, Adel Javanmard, Shang Tse Chuang, Sundar Iyer, Yi Lu

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Multi-banked embedded DRAM (eDRAM) has become increasingly popular in high-performance systems. However, the data retention problem of eDRAM is exacerbated by the larger number of banks and the high-performance environment in which it is deployed: The data retention time of each memory cell decreases while the number of cells to be refreshed increases. For this, multi-bank designs offer a concurrent refresh mode, where idle banks can be refreshed concurrently during read and write operations. However, conventional techniques such as periodically scheduling refreshes - with priority given to refreshes in case of conflicts with reads or writes - have variable performance, increase read latency, and can perform poorly in worst case memory access patterns. We propose a novel refresh scheduling algorithm that is low-complexity, produces near-optimal throughput with universal guarantees, and is tolerant to bursty memory access patterns. The central idea is to decouple the scheduler into two simple-to-implement modules: one determines which cell to refresh next and the other determines when to force an idle cycle in all banks. We derive necessary and sufficient conditions to guarantee data integrity for all access patterns, with any given number of banks, rows per bank, read/write ports and data retention time. Our analysis shows that there is a tradeoff between refresh overhead and burst tolerance and characterizes this tradeoff precisely. The algorithm is shown to be near-optimal and achieves, for instance, 76.6% reduction in worst-case refresh overhead from the periodic refresh algorithm for a 250MHz eDRAM with 10us retention time and 16 banks each with 128 rows. Simulations with Apex-Map synthetic benchmarks and switch lookup table traffic show that VR can almost completely hide the refresh overhead for memory accesses with moderate-to-high multiplexing across memory banks.

Original languageEnglish (US)
Title of host publicationSIGMETRICS/Performance 2012 - Proceedings of the 2012 ACM SIGMETRICS/Performance, Joint International Conference on Measurement and Modeling of Computer Systems
Pages247-258
Number of pages12
Edition1 SPEC. ISS.
DOIs
StatePublished - Aug 13 2012
Event12th Joint International Conference on Measurement and Modeling of Computer Systems, ACM SIGMETRICS/Performance 2012 - London, United Kingdom
Duration: Jun 11 2012Jun 15 2012

Publication series

NamePerformance Evaluation Review
Number1 SPEC. ISS.
Volume40
ISSN (Print)0163-5999

Other

Other12th Joint International Conference on Measurement and Modeling of Computer Systems, ACM SIGMETRICS/Performance 2012
CountryUnited Kingdom
CityLondon
Period6/11/126/15/12

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Keywords

  • embedded DRAM
  • memory refresh scheduling
  • multi-banked

ASJC Scopus subject areas

  • Software
  • Hardware and Architecture
  • Computer Networks and Communications

Cite this

Alizadeh, M., Javanmard, A., Chuang, S. T., Iyer, S., & Lu, Y. (2012). Versatile refresh: Low complexity refresh scheduling for high-throughput multi-banked eDRAM. In SIGMETRICS/Performance 2012 - Proceedings of the 2012 ACM SIGMETRICS/Performance, Joint International Conference on Measurement and Modeling of Computer Systems (1 SPEC. ISS. ed., pp. 247-258). (Performance Evaluation Review; Vol. 40, No. 1 SPEC. ISS.). https://doi.org/10.1145/2254756.2254787