Evaluating the Performance of Four Snooping Cache Coherency Protocols
Eggers, Susan J.
Katz, Randy H.
Technical Report Identifier: CSD-88-478
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.