Exploring memory consistency for massively-threaded throughput-oriented processors

Abstract

We re-visit the issue of hardware consistency models in the new context of massively-threaded throughput-oriented processors (MTTOPs). A prominent example of an MTTOP is a GPGPU, but other examples include Intel's MIC architecture and some recent academic designs. MTTOPs differ from CPUs in many significant ways, including their ability to tolerate latency, their memory system organization, and the characteristics of the software they run. We compare implementations of various hardware consistency models for MTTOPs in terms of performance, energy-efficiency, hardware complexity, and programmability. Our results show that the choice of hardware consistency model has a surprisingly minimal impact on performance and thus the decision should be based on hardware complexity, energy-efficiency, and programmability. For many MTTOPs, it is likely that even a simple implementation of sequential consistency is attractive.