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<p><b>Abstract</b>—Directory schemes have long been used to solve the cache coherence problem for large scale shared memory multiprocessors. In addition, tree-based protocols have been employed to reduce the directory size and the invalidation latency for a large degree of data sharing in the system. However, the existing tree-based protocols involve a very high communication overhead for maintaining a balanced tree, especially when the degree of data sharing is low. This paper presents a new tree-based cache coherence protocol which is a hybrid of the limited directory and the linked list schemes. By utilizing a limited number of pointers in the directory, the proposed protocol connects the nodes caching a shared block in a tree fashion without incurring any communication overhead. In addition to the low communication overhead, the proposed scheme also possesses the advantages of the existing bit-map and tree-based linked list protocols, namely, scalable memory requirement and logarithmic invalidation latency. We evaluate the performance of our protocol by running four applications on the Proteus execution-driven simulator. Our simulation results show that the performance of the proposed protocol is very close to that of the full-map protocol.</p>
Cache coherence, tree-based directory protocols, shared memory, large scale multiprocessors, execution-driven simulation.

Y. Chang and L. N. Bhuyan, "An Efficient Tree Cache Coherence Protocol for Distributed Shared Memory Multiprocessors," in IEEE Transactions on Computers, vol. 48, no. , pp. 352-360, 1999.
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