Spandex: A flexible interface for efficient heterogeneous coherence

Johnathan Alsop, Matthew D. Sinclair, Sarita V. Adve

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


Recent heterogeneous architectures have trended toward tighter integration and shared memory largely due to the efficient communication and programmability enabled by this shift. However, such integration is complex, because accelerators have widely disparate methods for accessing and keeping data coherent. Some processors use caches backed by hardware coherence protocols like MESI, while others prefer lightweight software coherence protocols or use specialized memories like scratchpads with differing state and communication granularities. Modern solutions tend to build interfaces that extend existing MESI-style CPU coherence protocols, often by adding hierarchical indirection through intermediate shared caches. Although functionally correct, these strategies lack flexibility and generally suffer from performance limitations that make them sub-optimal for some emerging accelerators and workloads. Instead, we need a flexible interface that can efficiently integrate existing and future devices – without requiring intrusive changes to their memory structure. We introduce Spandex, an improved coherence interface based on the simple and scalable DeNovo coherence protocol. Spandex (which takes its name from the flexible material commonly used in one-size-fits-all textiles) directly interfaces devices with diverse coherence properties and memory demands, enabling each device to communicate in a manner appropriate for its specific access properties. We demonstrate the importance of this flexibility by comparing this strategy against a more conventional MESI-based hierarchical solution for a diverse range of heterogeneous applications. On average for the applications studied, Spandex reduces execution time by 16% (max 29%) and network traffic by 27% (max 58%) relative to the MESI-based hierarchical solution.

Original languageEnglish (US)
Title of host publicationProceedings - 2018 ACM/IEEE 45th Annual International Symposium on Computer Architecture, ISCA 2018
PublisherInstitute of Electrical and Electronics Engineers Inc.
Number of pages14
ISBN (Electronic)9781538659847
StatePublished - Jul 19 2018
Event45th ACM/IEEE Annual International Symposium on Computer Architecture, ISCA 2018 - Los Angeles, United States
Duration: Jun 2 2018Jun 6 2018

Publication series

NameProceedings - International Symposium on Computer Architecture
ISSN (Print)1063-6897


Other45th ACM/IEEE Annual International Symposium on Computer Architecture, ISCA 2018
Country/TerritoryUnited States
CityLos Angeles

ASJC Scopus subject areas

  • Hardware and Architecture


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