Least Upper Delay Bound for VBR Flows in Networks-on-Chip with Virtual Channels
Fahimeh Jafari, Zhonghai Lu, Axel Jantsch · ACM Transactions on Design Automation of Electronic Systems · 2015
Real-time applications such as multimedia and gaming require stringent performance guarantees, usually enforced by a tight upper bound on the maximum end-to-end delay. For FIFO multiplexed on-chip packet switched networks we consider worst-case delay bounds for Variable Bit-Rate (VBR) flows with aggregate scheduling, which schedules multiple flows as an aggregate flow. VBR Flows are characterized by a maximum transfer size ( L ), peak rate ( p ), burstiness (σ), and average sustainable rate (ρ). Based on network calculus, we present and prove theorems to derive per-flow end-to-end Equivalent Service Curves (ESC), which are in turn used for computing Least Upper Delay Bounds (LUDBs) of individual flows. In a realistic case study we find that the end-to-end delay bound is up to 46.9% more accurate than the case without considering the traffic peak behavior. Likewise, results also show similar improvements for synthetic traffic patterns. The proposed methodology is implemented in C++ and has low run-time complexity, enabling quick evaluation for large and complex SoCs.