A tagless coherence directory

A key challenge in architecting a CMP with many cores is maintaining cache coherence in an efficient manner. Directory-based protocols avoid the bandwidth overhead of snoop-based protocols, and therefore scale to a large number of cores. Unfortunately, conventional directory structures incur significant area overheads in larger CMPs. The Tagless Coherence Directory (TL) is a scalable coherence solution that uses an implicit, conservative representation of sharing information. Conceptually, TL consists of a grid of small Bloom filters. The grid has one column per core and one row per cache set. TL uses 48% less area, 57% less leakage power, and 44% less dynamic energy than a conventional coherence directory for a 16-core CMP with 1MB private L2 caches. Simulations of commercial and scientific workloads indicate that TL has no statistically significant impact on performance, and incurs only a 2.5% increase in bandwidth utilization. Analytical modelling predicts that TL continues to ...

• Type: Conference
• Year: 2009
• Where: MICRO
• Authors: Jason Zebchuk, Vijayalakshmi Srinivasan, Moinuddin K. Qureshi, Andreas Moshovos
• Keywords: Cache Coherence, Coherence Directory, Hardware, MICRO 2009, Tagless Coherence Directory