Correct memory operation of cache-based multiprocessors

Abstract

This paper shows that cache coherence protocols can implement indivisible synchronization primitives reliably and can also enforce sequential consistency. Sequential consistency provides a commonly accepted model of behavior of multiprocessors. We derive a simple set of conditions needed to enforce sequential consistency in multiprocessors. These conditions are easily applied to prove the correctness of existing cache coherence protocols that rely on one or multiple broadcast buses to enforce atomicity of updates; in these protocols, all processing elements must be connected to the broadcast buses. The conditions are also used in this paper to establish new protocols which do not rely on the atomicity of updates and therefore do not require single access buses to propagate invalidations or to perform distributed WRITEs. It is also shown how such protocols can implement atomic READ&MODIFY operations for synchronization purposes.