Token Coherence is a new hardware technique for increasing the performance of commercial server workloads (e.g., database and web serving) running on moderate-sized multiprocessors. These shared-memory multiprocessor servers use cache-coherence protocols to provide the abstraction of a unified shared memory, and the performance of existing cache-coherence protocols is constrained either by requiring global message ordering or by the extra latency added by request indirections.

Token Coherence provides a framework for avoiding these performance bottlenecks by decoupling correctness requirements from performance optimizations. In this new framework, the correctness substrate provides strong correctness invariants involving token counting that guarantee correct behavior in all cases (without requiring ordering and indirections). A separate performance protocol provides high performance in the common case, relying on a more conservative (less efficient) mechanism only in rare cases. This approach (1) avoids request ordering, (2) reduces indirections, (3) enables predictive and adaptive techniques that can further increase performance and scalability, and (4) may reduce the verification effort required to eliminate protocol design errors that can cause data corruption.

Biographical sketch

Milo Martin is a PhD candidate and member of the Wisconsin Multifacet Project (http://www.cs.wisc.edu/multifacet/) at the University of Wisconsin-Madison. His research interests include memory system performance of commercial workloads, techniques to improve multiprocessor cache coherence, and use of dynamic feedback to build adaptive and robust systems.

Thursday, February 27, 2003
Moore School Bldg. - Room #216
3:00 - 4:30 p.m.