Improving multiprocessor performance with coarse-grain coherence tracking

To maintain coherence in conventional shared-memory multiprocessor systems, processors first check other processors´ 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%).