Nowadays available multiprocessor platforms predominantly use a Network-on-Chip (NoC) architecture as an interconnect medium, due to its good scalability and performance. During the last decade, NoCs received a significant amount of attention from the real-time community. One promising category of approaches suggests to employ already existing hardware features called virtual channels, and dedicate them, exclusively, to individual communication traffic flows. In this way, NoCs become more amenable to the real-time analysis, which is an essential requirement for providing both safe and tight worst-case analysis methods, and consequently deriving real-time guarantees. In this manuscript, we present the approach which falls in the aforementioned category. Specifically, we propose a novel method for the worst-case analysis of the NoC traffic, assuming the existence of per-flow dedicated virtual channels. Compared to the state-of-the-art techniques, our approach yields substantially tighter upper-bounds on the worst-case traversal times (WCTTs) of communication traffic flows. By employing the proposed method, resource over-provisioning can be mitigated to a large extent, and significant designcost reductions can be achieved. Moreover, we implemented a cycle-accurate simulator of the assumed NoC architecture, and used it to assess the tightness of derived WCTT bounds. Finally, we reached an interesting conclusion that bigger virtual channel buffers do not necessarily lead to better results, and in many cases can be counter-productive, which is a very important finding for system designers.

Abstract-This paper aims to reduce the pessimism of the analysis of the multi-point progressive blocking (MPB) problem in real-time priority-preemptive wormhole networks-on-chip. It shows that the amount of buffering on each network node can influence the worst-case interference that packets can suffer along their routes, and it proposes a novel analytical model that can quantify such interference as a function of the buffer size. It shows that, perhaps counter-intuitively, smaller buffers can result in lower upper-bounds on interference and thus improved schedulability. Didactic examples and large-scale experiments provide evidence of the strength of the proposed approach.

Preemptions via virtual channels have been proposed as a means to introduce the notion of priorities and real-time concepts in wormhole-switched NoC-based architectures. This work presents a holistic approach, which utilises a novel three-staged mapping method in order to assess what should be the physical characteristics of the platform (and its interconnect), such that real-time guarantees can be provided, assuming a given workload. We estimate the "gap" between platform characteristics required for the real-time analysis and those of currently available many-core platforms and propose to employ the existing feature of many-core platforms in order to significantly reduce this gap. The experiments demonstrate that virtual channels, an essential prerequisite for the real-time analysis, are not the bottleneck. The approach presented in this paper can help system designers to select/design the most suitable platform for a given workload, such that all temporal constraints are met and over-dimensioning is avoided.

Many-core" systems based on a Network-on-Chip (NoC) architecture offer various opportunities in terms of performance and computing capabilities, but at the same time they pose many challenges for the deployment of real-time systems, which must fulfill specific timing requirements at runtime. It is therefore essential to identify, at design time, the parameters that have an impact on the execution time of the tasks deployed on these systems and the upper bounds on the other key parameters. The focus of this work is to determine an upper bound on the traversal time of a packet when it is transmitted over the NoC infrastructure. Towards this aim, we first identify and explore some limitations in the existing recursive-calculus-based approaches to compute the Worst-Case Traversal Time (WCTT) of a packet. Then, we extend the existing model by integrating the characteristics of the tasks that generate the packets. For this extended model, we propose an algorithm called "Branch and Prune" (BP). Our proposed method provides tighter and safe estimates than the existing recursive-calculus-based approaches. Finally, we introduce a more general approach, namely "Branch, Prune and Collapse" (BPC) which offers a configurable parameter that provides a flexible trade-off between the computational complexity and the tightness of the computed estimate. The recursive-calculus methods and BP present two special cases of BPC when a trade-off parameter is 1 or ∞, respectively. Through simulations, we analyze this trade-off, reason about the implications of certain choices, and also provide some case studies to observe the impact of task parameters on the WCTT estimates. ACM Reference Format:Dakshina Dasari, Borislav Nikolić, Vincent Nélis, and Stefan M. Petters. 2014. NoC contention analysis using a branch-and-prune algorithm.