Evaluating the performance of four snooping cache coherency protocols

  • Authors:
  • S. J. Eggers;R. H. Katz

  • Affiliations:
  • Department of Computer Science, FR-35, University of Washington, Seattle, WA;Computer Science Division, Dept. of Electrical Engineering & Computer Science, University of California, Berkeley, California

  • Venue:
  • ISCA '89 Proceedings of the 16th annual international symposium on Computer architecture
  • Year:
  • 1989

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Abstract

Write-invalidate and write-broadcast coherency protocols have been criticized for being unable to achieve good bus performance across all cache configurations. In particular, write-invalidate performance can suffer as block size increases; and large cache sizes will hurt write-broadcast. Read-broadcast and competitive snooping extensions to the protocols have been proposed to solve each problem.Our results indicate that the benefits of the extensions are limited. Read-broadcast reduces the number of invalidation misses, but at a high cost in processor lockout from the cache. The net effect can be an increase in total execution cycles. Competitive snooping benefits only those programs with high per-processor locality of reference to shared data. For programs characterized by inter-processor contention for shared addresses, competitive snooping can degrade performance by causing a slight increase in bus utilization and total execution time.