Closing the Window of Vulnerability in Multiphase Memory Transactions

Multiprocessor architects have begun to explore several mech-anisms such as prefetching, context-switching and softwsre-assisted dynamic cache-coherence, which transform single-phase memory transactions in conventional memory systems into mul-tiphase operations. Multiphase operations introduce a window of vulnerability in which data can be invalidated before it is used. Losing data due to invalidations introduces damaging livelock situations. This paper discusses the origins of the window of vul-nerability and proposes an architectural framework that closes it. The framework is implemented in Alewife, a large-scale multi-processor being built at MIT.