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Cache coherence problem is a major issue in the design of shared-memory multiprocessors. As the number of processors grows, traditional busbased snoopy schemes for cache coherence are no longer adequate. Instead, the directory-based scheme is a promising alternative for the largescale cache coherence problem. However, the storage overhead of (full-map) directory scheme may become too prohibitive as the system size goes up. This paper presents two distributed directory schemes, the tree directory and the hierarchical full-map directory, to deal with the storage overhead problem. Preliminary tracedriven evaluations show that the performance of our schemes compares favorably to the fullmap directory scheme, while reducing the storage overhead by over 90%. These two schemes should lend themselves to the design and implementation of large-scale cache coherent multiprocessors.-11 -

With the ever increasing needs of power aware architecture and circuit design in recent years, how to reduce the power consumption of processors without sacrificing performance has become an important issue. In this paper, we propose a new method for low power branch predictionHedging Filter, which combines filtering scheme reducing dynamic power consumption with hedging prediction mechanism lowering static power dissipation. We analyze and empirically study this proposed scheme embodied in the Sentry Table-Complementary Branch Prediction combo with respect to critical path delay, performance, hardware overhead and power consumption. Hedging Filter not only preserves critical path delay and prediction accuracy, but also contributes to the savings of dynamic and static power. From our evaluation, presuming equivalent or superior performance with respect to traditional counterparts, the proposed method reduces branch prediction hardware cost by up to 71% and power saving by up to 79% respectively.

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