The performance of NoCs for very large manycore systems under locality-based traffic

The scaling of semiconductor technologies is leading to processors with increasing numbers of cores. A key enabler in manycore systems is the use of Networks-on-Chip (NoC) as a global communication mechanism. The adoption of NoCs in manycore systems requires a shift in focus from computation to communication, as communication is fast becoming the dominant factor in processor performance. In large manycore systems, performance is predicated on the locality of communication. In this work, we investigate the performance of three NoC topologies for systems with thousands of processor cores under two types of localised traffic models. We present latency and throughput results comparing fat quadtree, concentrated mesh and mesh topologies under different degrees of localisation. Our results, obtained using a modified version of the HNOCS NoC simulator and based on the ITRS physical data for 2023, show that the type of locality traffic and the degree of localisation significantly affects the NoC performance, and that scale-invariant topologies perform worse than flat topologies.