Interaction of NoC Design and Coherence Protocol in 3D-Stacked CMPs

Computer architectures have evolved to structures where communication has become an essential part of the system and most of it currently takes place inside the chip. The number of on-Chip cores and the available off-chip bandwidth is not growing at the same rate. This demands for the inclusion of more sophisticated memory hierarchies inside the chip to deal with off-chip latency and bandwidth problems in order to keep on improving performance. The exhaustion of Moore´s law will accelerate the use of 3D-Stacked on-chip memory hierarchies to sustain the required scalability of forthcoming CMPs. For this class of systems´ memory hierarchy, coherence protocol and interconnection network are two closely related components, but which are usually designed independently. In this work we will demonstrate that network components can be coupled to coherence protocol in order to extract significant performance benefits. Making use of a well-known snoop coherence protocol, we will present different network optimizations, better able to adapt to the communication requirements of this protocol. Evaluation results show that with minimal hardware changes, for some real applications, full system performance can be improved by up to 48%.