ROAdNoC: runtime observability for an adaptive network on chip architecture

Hard-to-predict system behavior and/or reliability issues resulting from migrating to new technology nodes requires considering runtime adaptivity in future on-chip systems. Runtime observability is a prerequisite for runtime adaptivity as it is providing necessary system information gathered on-the-fly. We are presenting the first comprehensive runtime observability infrastructure for an adaptive network on chip architecture which is flexible (e.g. in choosing the routing path), hardly intrusive, and requires little additional overhead (around 0.7% of the total link bandwidth). The hardware overhead is negligible, too, and is in fact less than the hardware savings due to resource multiplexing capabilities that are achieved through runtime observability/adaptivity. As an example, our on-demand buffer assignment scheme increases the buffer utilization and decreases the overall buffer requirements by an average of 42% (the buffer area amounts to about 60% of the entire router area [19]) in our case study analysis compared to a fixed buffer assignment scheme [7]. Our runtime observability on an average also increases the connection success rate by 62% compared to the case without runtime observability for the applications from the E3S benchmark suite [6]. We show the advantages obtained through runtime observability and compare with state-of-the art communication-centric designs.