Improving Multiprocessor Performance with Coarse-Grain Coherence Tracking

To main coherence in conventional shared-memory multiprocessor systems, processors first check other proessors' caches before obtaining data from memory. This coherence checking adds latency to memory requests and leads to large amounts of interconnect traffic in broadcast-based systems. Our results for a set of commercial, scientific and multiprogrammed workloads show that on average 67% (and up to 94%) of broadcasts are unnecessary. Coarse-Grain Coherence Tracking is a new technique that supplements a conventional coherence mechanism and optimizes the performance of coherence enforcement. The Coarse-Grain Coherence mechanism monitors the coherence status of large regions of memory, and uses that information to avoid unnecessary broadcasts. Coarse-Grain Coherence Tracking is shown to eliminate 55-97% of the unnecessary broadcasts, and improve performance by 8.8% on average (and up to 21.7%).