NoCo: ILP-based worst-case contention estimation for mesh real-time manycores

Manycores are capable of providing the computational demands required by functionally-advanced critical applications in domains such as automotive and avionics. In manycores a network-on-chip (NoC) provides access to shared caches and memories and hence concentrates most of the contention that tasks suffer, with effects on the worst-case contention delay (WCD) of packets and tasks' WCET. While several proposals minimize the impact of individual NoC parameters on WCD, e.g. mapping and routing, there are strong dependences among these NoC parameters. Hence, finding the optimal NoC configurations requires optimizing all parameters simultaneously, which represents a multidimensional optimization problem. In this paper we propose NoCo, a novel approach that combines ILP and stochastic optimization to find NoC configurations in terms of packet routing, application mapping, and arbitration weight allocation. Our results show that NoCo improves other techniques that optimize a subset of NoC parameters.This work has been partially supported by the Spanish Ministry of Economy and Competitiveness under grant TIN2015- 65316-P and the HiPEAC Network of Excellence. It also received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (agreement No. 772773). Carles Hernández is jointly supported by the MINECO and FEDER funds through grant TIN2014-60404-JIN. Jaume Abella has been partially supported by the Spanish Ministry of Economy and Competitiveness under Ramon y Cajal postdoctoral fellowship number RYC-2013-14717. Enrico Mezzetti has been partially supported by the Spanish Ministry of Economy and Competitiveness under Juan de la Cierva-Incorporaci´on postdoctoral fellowship number IJCI-2016-27396.Peer ReviewedPostprint (author's final draft

Accurately Measuring Contention in Mesh NoCs in Time-Sensitive Embedded Systems

[EN] The computing capacity demanded by embedded systems is on the rise as software implements more functionalities, ranging from best-effort entertainment functions to performance-guaranteed safety-related functions. Heterogeneous manycore processors, using wormhole mesh (wmesh) Network-on-Chips (NoCs) as the main communication means, and contention block among applications, are increasingly considered to deliver the required computing performance. Most research efforts on software timing analysis have focused on deriving bounds (estimates) to the contention that tasks can suffer when accessing wmesh NoCs. However, less effort has been devoted to an equally important problem, namely, accurately measuring the actual contention tasks generate each other on the wmesh which is instrumental during system validation to diagnose any software timing misbehavior and determine which tasks are particularly affected by contention on specific wmesh routers. In this article, we work on the foundations of contention measuring in wmesh NoCs and propose and explain the rationale of a golden metric, called task PairWise Contention (PWC). PWC allows ascribing the actual share of the contention a given task suffers in the wmesh to each of its co-runner tasks at packet level. We also introduce and formalize a Golden Reference Value (GRV) for PWC that specifically defines a criterion to fairly break down the contention suffered by a task among its co-runner tasks in the wmesh. Our evaluation shows that GRV effectively captures how contention occurs by identifying the actual core (task) causing contention and whether contention is caused by local or remote interference in the wmesh.This work has been supported by the Spanish Ministry of Science and Innovation under grant PID2019-107255GB-C21 funded by MCIN/AEI/10.13039/501100011033 and the European Research Council (ERC) under the EU's Horizon 2020 research and innovation programme (grant agreement No. 772773).Cardona, J.; Hernández Luz, C.; Abella, J.; Mezzetti, E.; Cazorla, FJ. (2023). Accurately Measuring Contention in Mesh NoCs in Time-Sensitive Embedded Systems. ACM Transactions on Design Automation of Electronic Systems. 28(3). https://doi.org/10.1145/358200628

Buffer-Aware Worst-Case Timing Analysis of Wormhole NoCs Using Network Calculus

Abstract—Conducting worst-case timing analyses for wormhole Networks-on-chip (NoCs) is a fundamental aspect to guarantee real-time requirements, but it is known to be a challenging issue due to complex congestion patterns that can occur. In that respect, we introduce in this paper a new buffer-aware timing analysis of wormhole NoCs based on Network Calculus. Our main idea consists in considering the flows serialization phenomena along the path of a flow of interest (f.o.i), by paying the bursts of interfering flows only at the first convergence point, and refining the interference patterns for the f.o.i accounting for the limited buffer size. Moreover, we aim to handle such an issue for wormhole NoCs, implementing a fixed priority-preemptive arbitration of Virtual Channels (VCs), that can be assigned to an arbitrary number of traffic classes with different priority levels, i.e. VC sharing, and each traffic class may contain an arbitrary number of flows, i.e. priority sharing. It is worth noting that such characteristics cover a large panel of wormhole NoCs. The derived delay bounds are analyzed and compared to available results of existing approaches, based on Scheduling Theory as well as Compositional Performance Analysis (CPA). In doing this, we highlight a noticeable enhancement of the delay bounds tightness in comparison to CPA approach, and the inherent safe bounds of our proposal in comparison to Scheduling Theory approaches. Finally, we perform experiments on a manycore platform, to confront our timing analysis predictions to experimental data and assess its tightness

Integrating wireless technologies into intra-vehicular communication

With the emergence of connected and autonomous vehicles, sensors are increasingly deployed within car. Traffic generated by these sensors congest traditional intra-vehicular networks, such as CAN buses. Furthermore, the large amount of wires needed to connect sensors makes it hard to design cars in a modular way. These limitations have created impetus to use wireless technologies to support intra-vehicular communication. In this dissertation, we tackle the challenge of designing and evaluating data collection protocols for intra-car networks that can operate reliably and efficiently under dynamic channel conditions. First, we evaluate the feasibility of deploying an intra-car wireless network based on the Backpressure Collection Protocol (BCP), which is theoretically proven to be throughput-optimal. We uncover a surprising behavior in which, under certain dynamic channel conditions, the average packet delay of BCP decreases with the traffic load. We propose and analyze a queueing-theoretic model to shed light into the observed phenomenon. As a solution, we propose a new protocol, called replication-based LIFO-backpressure (RBL). Analytical and simulation results indicate that RBL dramatically reduces the delay of BCP at low load, while maintaining its high throughput performance. Next, we propose and implement a hybrid wired/wireless architecture, in which each node is connected to either a wired interface or a wireless interface or both. We propose a new protocol, called Hybrid-Backpressure Collection Protocol (Hybrid-BCP), for the intra-car hybrid networks. Our testbed implementation, based on CAN and ZigBee transceivers, demonstrates the load balancing and routing functionalities of Hybrid-BCP and its resilience to DoS attacks. We further provide simulation results, obtained based on real intra-car RSSI traces, showing that Hybrid-BCP can achieve the same performance as a tree-based protocol while reducing the radio transmission power by a factor of 10. Finally, we present TeaCP, a prototype Toolkit for the evaluation and analysis of Collection Protocols in both simulation and experimental environments. TeaCP evaluates a wide range of standard performance metrics, such as reliability, throughput, and latency. TeaCP further allows visualization of routes and network topology evolution. Through simulation of an intra-car WSN and real lab experiments, we demonstrate the functionality of TeaCP for comparing different collection protocols

Time-Randomized Wormhole NoCs for Critical Applications

Wormhole-based NoCs (wNoCs) are widely accepted in high-performance domains as the most appropriate solution to interconnect an increasing number of cores in the chip. However, wNoCs suitability in the context of critical real-time applications has not been demonstrated yet. In this article, in the context of probabilistic timing analysis (PTA), we propose a PTA-compatible wNoC design that provides tight time-composable contention bounds. The proposed wNoC design builds on PTA ability to reason in probabilistic terms about hardware events impacting execution time (e.g., wNoC contention), discarding those sequences of events occurring with a negligible low probability. This allows our wNoC design to deliver improved guaranteed performance w.r.t. conventional time-deterministic setups. Our results show that performance guarantees of applications running on top of probabilistic wNoC designs improve by 40% and 93% on average for 4 × 4 and 6 × 6 wNoC setups, respectively.The research leading to these results has received funding from the European Community's Seventh Framework Programme [FP7/2007-2013] under the PROXIMA Project (www.proxima-project.eu), grant agreement no 611085. This work has also been partially supported by the Spanish Ministry of Science and Innovation under grant TIN2015-65316-P and the HiPEAC Network of Excellence. Mladen Slijepcevic is funded by the Obra Social Fundación la Caixa under grant Doctorado \la Caixa" - Severo Ochoa. Carles Hernández is jointly funded by the Spanish Ministry of Economy and Competitiveness (MINECO) and FEDER funds through grant TIN2014-60404-JIN. Jaume Abella has been partially supported by the MINECO under Ramon y Cajal postdoctoral fellowship number RYC-2013-14717.Peer ReviewedPostprint (author's final draft