Predictable composition of memory accesses on many-core processors

International audienceThe use of many-core COTS processors in safety critical embedded systems is a challenging research topic. The predictable execution of several applications on those processors is not possible without a precise analysis and mitigation of the possible sources of interference. In this paper, we identify the external DDR-SDRAM and the Network on Chip to be the main bottlenecks for both average performance and predictability in such platforms. As DDR-SDRAM memories are intrinsically stateful, the naive calculation of the Worst-Case Execution Times (WCETs) of tasks involves a significantly pessimistic upper-bounding of the memory access latencies. Moreover, the worst-case end-to-end delays of wormhole switched networks cannot be bounded without strong assumptions on the system model because of the possibility of deadlock. We provide an analysis of each potential source of interference and we give recommendations in order to build viable execution models enabling efficient composable computation of worst-case end-to-end memory access latencies compared to the naive worst-case-everywhere approach

Computational trust and reputation models for open multi-agent systems: a review

In open environments, agents depend on reputation and trust mechanisms to evaluate the behavior of potential partners. The scientific research in this field has considerably increased, and in fact, reputation and trust mechanisms have been already considered a key elements in the design of multi-agent systems. In this paper we provide a survey that, far from being exhaustive, intends to show the most representative models that currently exist in the literature. For this enterprise we consider several dimensions of analysis that appeared in three existing surveys, and provide new dimensions that can be complementary to the existing ones and that have not been treated directly. Moreover, besides showing the original classification that each one of the surveys provide, we also classify models that where not taken into account by the original surveys. The paper illustrates the proliferation in the past few years of models that follow a more cognitive approach, in which trust and reputation representation as mental attitudes is as important as the final values of trust and reputation. Furthermore, we provide an objective definition of trust, based on Castelfranchi's idea that trust implies a decision to rely on someone. © 2011 Springer Science+Business Media B.V.This work was supported by the EC by the project LiquidPub (STREP FP7-213360), by the Spanish Education and Science Ministry with the projects AEI (TIN2006-15662-C02-01), AT (CONSOLIDER CSD2007-0022, INGENIO 2010) and RepBDI (Intramural 200850I136), and by the Generalitat de Catalunya under the grants 2009-SGR-1433 and 2009-SGR-1434.Peer Reviewe

Temporal isolation of hard real-time applications on many-core processors

International audienceMany-core processors offer massively parallel computation power representing a good opportunity for the design of highly integrated avionics systems. Such designs must face several challenges among which 1) temporal isolation must be ensured between applications and 2) bounds of WCET must be computed for real-time safety critical applications. In order to partially address those issues, we propose an appropriate execution model, that restricts the applications behaviours, which has been implemented on the Kalray MPPA-256. We tested the correctness of the approach through a series of benchmarks and the implementation of a case study.Les processeurs pluri-coeurs offrent une puissance de calcul massivement parallèle représentant une opportunité pour la conception de systèmes avioniques hautement intégrés. Ces systèmes impliquent plusieurs problèmes parmi lesquels: 1) une isolation temporelle doit être assurée entre les applications et 2) des bornes sur les WCETs des programmes temps-réel critiques doivent être calculées. Afin de résoudre partiellement ces problèmes, nous proposons un modèle d'exécution restreignant le comportement des applications exécutées sur le MPPA-256 de Kalray. De plus, nous montrons que l'approche est correcte au travers des plusieurs benchmarks et l'implémentation d'un cas d'étude