Cloak: Tolerating Non-Volatile Cache Read Latency

Apostolos Kokolis, Namrata Mantri, Shrikanth Ganapathy, Josep Torrellas, John Kalamatianos

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


The increased memory demands of workloads are putting high pressure on Last Level Caches (LLCs). In general, there is limited opportunity to increase the capacity of LLCs due to the area and power requirements of the underlying SRAM technology. Interestingly, emerging Non-Volatile Memory (NVM) technologies promise a feasible alternative to SRAM for LLCs due to their higher area density. However, NVMs have substantially higher read and write latencies, which offset their density benefit. Although researchers have proposed methods to tolerate NVM's higher write latency, little emphasis has been placed on the critical NVM read latency. To address this problem, this paper proposes Cloak. Cloak exploits page-level data reuse in the LLC, to hide NVM read latency. Specifically, on certain L1 DTLB misses, Cloak transfers LLC-resident data belonging to the TLB-missing page from the LLC NVM array to a set of small SRAM Page Buffers that will service subsequent requests to this page. Further, to enable the high-bandwidth, low-latency transfer of lines of a page to the page buffers, Cloak uses an LLC layout that accelerates the discovery of LLC-resident cache lines from the page. We evaluate Cloak with full-system simulations of a 4-core processor across 14 workloads. We find that, on average, a machine with Cloak is faster than one with an SRAM LLC by 23.8% and one with an NVM-only LLC by 8.9%-in both cases, with negligible change in area. Further, Cloak reduces the ED2 metric relative to these designs by 39.9% and 17.5%, respectively.

Original languageEnglish (US)
Title of host publicationProceedings of the 36th ACM International Conference on Supercomputing, ICS 2022
PublisherAssociation for Computing Machinery
ISBN (Electronic)9781450392815
StatePublished - Jun 28 2022
Event36th ACM International Conference on Supercomputing, ICS 2022 - Virtual, Online
Duration: Jun 27 2022Jun 30 2022

Publication series

NameProceedings of the International Conference on Supercomputing


Conference36th ACM International Conference on Supercomputing, ICS 2022
CityVirtual, Online


  • Cache hierarchy
  • Last level cache
  • Non-volatile memory

ASJC Scopus subject areas

  • General Computer Science


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