Dynamic self-invalidation: reducing coherence overhead in shared-memory multiprocessors

  • Authors:
  • Alvin R. Lebeck;David A. Wood

  • Affiliations:
  • Computer Sciences Department, University of Wisconsin-Madison, Madison, Wisconsin;Computer Sciences Department, University of Wisconsin-Madison, Madison, Wisconsin

  • Venue:
  • ISCA '95 Proceedings of the 22nd annual international symposium on Computer architecture
  • Year:
  • 1995

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Abstract

This paper introduces dynamic self-invalidation (DSI), a new technique for reducing cache coherence overhead in shared-memory multiprocessors. DSI eliminates invalidation messages by having a processor automatically invalidate its local copy of a cache block before a conflicting access by another processor. Eliminating invalidation overhead is particularly important under sequential consistency, where the latency of invalidating outstanding copies can increase a program's critical path.DSI is applicable to software, hardware, and hybrid coherence schemes. In this paper we evaluate DSI in the context of hardware directory-based write-invalidate coherence protocols. Our results show that DSI reduces execution time of a sequentially consistent full-map coherence protocol by as much as 41%. This is comparable to an implementation of weak consistency that uses a coalescing write-buffer to allow up to 16 outstanding requests for exclusive blocks. When used in conjunction with weak consistency, DSI can exploit tear-off blocks---which eliminate both invalidation and acknowledgment messages---for a total reduction in messages of up to 26%.