2010 19th International Conference on Parallel Architectures and Compilation Techniques (PACT) (2010)
Sept. 11, 2010 to Sept. 15, 2010
DOI Bookmark: http://doi.ieeecomputersociety.org/
Nick Barrow-Williams , Computer Laboratory, University of Cambridge, CB3 0FD, UK
Christian Fensch , School of Informatics, University of Edinburgh, EH8 9AB, UK
Simon Moore , Computer Laboratory, University of Cambridge, CB3 0FD, UK
Many-core architectures provide an efficient way of harnessing the increasing numbers of transistors available in modern fabrication processes. While they are similar to multi-node systems, they exhibit different communication latency and storage characteristics, providing new design opportunities that were previously not feasible. Traditional cache coherence protocols, although often used in many-core designs, have been developed in the context of multi-node systems. As such, they seldom take advantage of the new possibilities that many-core architectures offer. We propose Proximity Coherence, a scheme in which L1 load misses are optimistically forwarded to nearby caches via new dedicated links rather than always being indirected via a directory structure. Such an optimization is made possible by the comparable cost of local cache accesses with the use of on-chip network resources. Coherency is maintained using lightweight graph structures embedded in the L1 caches. We compare our Proximity Coherence protocol to an existing directory-based MESI protocol using full-system simulations of a 32 core system. Our extension lowers the latency of L1 cache load misses by up to 32% while reducing the bytes transferred on the global on-chip interconnect by up to 19% for a range of parallel benchmarks. Employing Proximity Coherence provides execution time improvements of up to 13%, reduces cache hierarchy energy consumption by up to 30% and delivers a more efficient solution to the challenge of coherence in chip multiprocessors.
network-on-chip, Proximity Coherence, CMP, cache design
N. Barrow-Williams, C. Fensch and S. Moore, "Proximity coherence for chip multiprocessors," 2010 19th International Conference on Parallel Architectures and Compilation Techniques (PACT), Vienna, Austria, 2010, pp. 123-134.