Dynamic Guaranteed Service Communication on Best-Effort Networks-on-Chip

In order to execute applications under real-time constraints on many-core processors with a Network-on-Chip (NoC), guaranteed service (GS) communication with guaranteed end-to-end latency and bandwidth is required. Several hardware-based solutions for GS communication have been proposed in literature. However, commercially available many-core processors, e.g., Tilera's TilePro64 or Adapteva's Epiphany, do not support such features. In this paper, we propose a software solution that allows GS communication on 2D-mesh packet-switching NoCs. Our investigation is based on a hardware model that is applicable to commercially available processors, which include multiple NoCs to separate request and response packets and support only best-effort communication. We prove that a common upper bound of the injection rate for all sources limits the congestion which leads to an upper bound of the worst-case transmission latency (WCTL) for any transmission, i.e., the combination of a request and a response packet. Furthermore, our approach supports arbitrary transmission streams that can be modified at runtime without violating the upper bound of the WCTL, as long as the injection rate is not violated. This enables adaptive features such as task migration or dynamic scheduling policies. Experiments evaluate our solution for different traffic patterns.