Closing the Window of Vulnerability in Multiphase Memory Transactions

Multiprocessor architects have begun to explore several mechanisms such as prefetching, context-switching and software-assisted dynamic cache-coherence, which transform single-phase memory transactions in conventional memory systems into multiphase 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 vulnerability and proposes an architectural framework that closes it. The framework is implemented in Alewife, a large-scale multiprocessor being built at MIT. 1 Introduction One of the major thrusts of multiprocessor research has been the exploration of mechanisms that provide ease of programming, yet are amenable to cost-effective implementation. To this end, a substantial effort has been expended in providing efficient shared memory for systems with large numbers of processors. Many of the mecha..