Evaluation of Two Optimized Protocols for Sequential Consistency

Sequential consistency is a well known consistency requirement for distributed shared memory. However, most of the algorithms that implement sequential consistency involve some expensive blocking. In this paper, we propose algorithms that reduce blocking. First, we propose a synchronous algorithm using a 3-phase protocol and, when it is possible, a more e�cient 2-phase protocol. We also propose a semi-synchronous algorithm where all processes can proceed asynchronously until a speci�c operation, called the �ush, is invoked. The processes are then synchronized by this �ush at a particular point in space and time. Subsequently, all processes resume their asynchronous progress. Simulation results show signi�cant improvements in performance in our protocols, especially in the case of the semi-synchronous protocol