NoC Architectures for Silicon Interposer Systems: Why Pay for more Wires when you Can Get them (from your interposer) for Free?

Silicon interposer technology ("2.5D" stacking) enables the integration of multiple memory stacks with a processor chip, thereby greatly increasing in-package memory capacity while largely avoiding the thermal challenges of 3D stacking DRAM on the processor. Systems employing interposers for memory integration use the interposer to provide point-to-point interconnects between chips. However, these interconnects only utilize a fraction of the interposer's overall routing capacity, and in this work we explore how to take advantage of this otherwise unused resource. We describe a general approach for extending the architecture of a network-on-chip (NoC) to better exploit the additional routing resources of the silicon interposer. We propose an asymmetric organization that distributes the NoC across both a multi-core chip and the interposer, where each sub-network is different from the other in terms of the traffic types, topologies, the use or non-use of concentration, direct vs. Indirect network organizations, and other network attributes. Through experimental evaluation, we show that exploiting the otherwise unutilized routing resources of the interposer can lead to significantly better performance.