Interconnections in multi-core architectures: understanding mechanisms, overheads and scaling

This paper examines the area, power, performance, and design issues for the on-chip interconnects on a chip multiprocessor, attempting to present a comprehensive view of a class of interconnect architectures. It shows that the design choices for the interconnect have significant effect on the rest of the chip, potentially consuming a significant fraction of the real estate and power budget. This research shows that designs that treat interconnect as an entity that can be independently architected and optimized would not arrive at the best multi-core design. Several examples are presented showing the need for careful co-design. For instance, increasing interconnect bandwidth requires area that then constrains the number of cores or cache sizes, and does not necessarily increase performance. Also, shared level-2 caches become significantly less attractive when the overhead of the resulting crossbar is accounted for. A hierarchical bus structure is examined which negates some of the performance costs of the assumed base-line architecture.