Monday, March 12, 2001
11:00 AM
CSB 209
Mark Hill
U. Wisc. - Madison
Wisconsin Multifacet: Extending Snooping
Shared-memory multiprocessor servers provide an important foundation for the Internet by running many commercial workloads. Most multiprocessors today are symmetric multiprocessors (SMP) that implement snooping cache coherence. Nevertheless, many argue that SMPs will be supplanted by directory-based multiprocessors due to (1) the inefficient nature of snooping's broadcast and (2) the increased difficulty of building physical or logical buses.

The WISCONSIN MULTIFACET PROJECT is performing research to improve multiprocessor servers for commercial workloads. Relative to scientific workloads, we find commercial applications use fewer processors and suffer many more sharing misses that must be satisfied by other processors. Both aspects suggest that extending snooping cache coherence might be more attractive than switching to directory protocols.

This talk will discuss two complementary proposals for mitigating the twin concerns regarding snooping. First, MULTICAST SNOOPING [ISCA '99] reduces snooping's bandwidth requirements by using selective multicasts rather than always broadcasting. Second, TIMESTAMP SNOOPING [ASPLOS '00] allows designers to implement snooping on any interconnect topology by implicitly attaching logical timestamps to coherence transactions. The presentation will spend more time on the newer timestamp snooping proposal. C.f.