Transport haute-performance: problématique et solutions proposées

L'univers du calcul haute-performance a découvert des limitations du protocole TCP, l'empêchant d'utiliser pleinement les liens haut-débit et grande distance prévus pour former l'ossature des grilles de calcul. Cet article présente ces problèmes de performance, puis décrit, analyse et compare les solutions actuellement proposées par la communauté réseau.RES-

Existence de dykes doléritiques anciens à composition de tholéiites continentales au sein de la province alcaline de la ligne du Cameroun. Implication sur le contexte géodynamique

n the Adamawa Plateau (Northern Cameroon), doleritic dykes belong to a magmatic activity which predated the Cenozoic alkaline volcanism of the Cameroon Line. They have the chemical composition of continental tholeiites with Nb-Ta- and Ti-negative anomalies. This magmatism is interpreted as being derived from a sub-continental lithospheric source, which may have been contaminated during a former subduction event, linked to the Pan-African convergence. It is related to an early stage of continental break-up, which was contemporaneous or predated the Cretaceous tholeiitic magmatism of predominantly asthenospheric origin, which indicates a lithospheric thinning

An Efficient Network API for in-Kernel Applications in Clusters

International audienceRunning parallel applications on clusters with high-speed local networks requires fast communication between computing nodes but also low latency and high bandwidth file access. However, the application programming interfaces of high-speed local networks were designed for MPI communication and do not always meet the requirements of other applications like distributed file systems. In this paper, we explore several solutions to improve the use of high-speed network for in-kernel applications. Distributed file systems implemented on top of the GM interface of Myrinet are first examined to demonstrate how hard it is to get an efficient interaction between such applications and the network. Then, we propose solutions to simplify and improve this interaction and integrate them into the kernel interface of the new Myrinet. Performance comparisons between MX and GM, and their usage in both a distributed file system and a zero-copy protocol show nice improvements. Moreover, we are able to improve the performance of the flexible kernel API we designed in MX that allows to remove some intermediate copy

Impact of the Correlation between Flow Rates and Durations on the Large-Scale Properties of Aggregate Network Traffic

Since the discovery of long-range dependence in network traffic in 1993, many models have appeared to reproduce this property, based on heavy-tailed distributions of some flow-scale properties of the traffic. However, none of these models consider the correlation existing between flow rates and flow durations. In this work, we extend previously proposed models to include this correlation. Based on a planar Poisson process setting, which describes the flow-scale traffic structure, we analytically compute the auto-covariance function of the aggregate traffic's bandwidth and show that it exhibits long-range dependence with a different Hurst parameter. In uncorrelated case, the model that we propose is consistent with existing models, and predict the same Hurst parameter. We also prove that pseudo long-range dependence with a different index can arise from highly variable flow rates. The pertinence of our model choices is validated on real web traffic traces

Towards a User-Oriented Benchmark for Transport Protocols Comparison in very High Speed Networks

Standard TCP faces some performance limitations in very high speed wide area networks, mainly due to a long end-to-end feedback loop and a conservative behaviour with respect to congestion. Many TCP variants have been proposed to overcome these limitations. However, TCP is a complex protocol with many user-configurable parameters and a range of different implementations. It is then important to define measurement methods so that the transport services and protocols can evolve guided by scientific principles and compared quantitatively. The goal of this report is to present some steps towards a user-oriented benchmark, called ITB, for high speed transport protocols comparison. We first present and analyse some results reported in the literature. From this study we identify classes of representative applications and useful metrics. We then isolate infrastructure parameters and traffic factors which influence the protocol behaviour. This enable us to define scenario capturing and synthesising comprehensive and useful properties. We finally illustrate this proposal by preliminary results obtained on our experimental environment, Grid'5000, we have built and are using for contributing in this benchmark design

L'expression du temps et de l'espace dans le roman de Nathalie Sarraute "Vous les entendez?"

Problem/Fragestellungen : Die vorliegende Arbeit versteht sich als eine Untersuchung der Beziehungen zwischen Zeit und Raum im Roman von Nathalie Sarraute Vous les entendez?. Ausgehend von der Tatsache, dass ein literarischer Text, als komplexe Struktur, einer multidisziplinären Analyse unterzogen werden muss, und dass die Kriterien für diese Analyse zurzeit noch in der Anfangsphase in der Textlinguistik sind, versuchen wir diese zu definieren und das mit dem Ziel, die Besonderheiten des Chronotopos zu analysieren. Wir stellen die Frage, inwiefern die Berücksichtigung von solchen Aspekten wie die Entstehung des Werkes, sein geschichtliches, literarisches und soziales Umfeld ebenso wie die Ästhetik und die Schreibweise des Autors, beiträgt, die Besonderheiten der Zeit-Raum Beziehungen in diesem Werk zu bestimmen. Außerdem stellen wir in dieser Arbeit die folgende Frage: Wie kann das Werk von Nathalie Sarraute, Vertreterin einer modernen Tendenz in der französischen Literatur, die neuen Verfahren mit jenen des „klassischen“ Romans „versöhnen“. Methodisches Vorgehen: Die methodische Umsetzung der Studie über die Zeit-Raum Bestimmungen im Roman Vous les entendez? beruht auf der fortlaufenden Analyse des Sujets, der Hauptthemen des Romans und der von ihnen bestimmten Chronotopoi. Die qualitative Textanalyse mit Berücksichtigung der besonderen Schreibweise von Nathalie Sarraute hat uns ermöglicht, die lexikalischen, grammatikalischen, syntaktischen und stilistischen Mittel der Darstellung der Zeit-Raum Beziehungen im Roman Vous les entendez? zu charakterisieren. Hauptsächliche Ergebnisse: Der Chronotopos im Roman Vous les entendez? ist organisiert in Zusammenhang mit den Merkmalen der von der Autorin dargestellten Realität der Tropismen. So werden die endlos vergrößerten geschlossenen Räumlichkeiten im Roman in Zusammenhang mit einer Zeit gebracht, die als geschlossen zu betrachten ist und die jeder dynamischen Komponente entbehrt. Diese sonderbare Anordnung der Zeit-Raum Elemente entspricht den Entwicklungstendenzen in der Gattung des Romans. Jedoch ist diese Schreibform doch nicht ganz von den Konventionen der traditionellen Literatur befreit. Zum Großteil ist ihre Durchführung mit dem Funktionieren der linguistischen Mittel im Text verbunden

Executing distributed applications on virtualized infrastructures specified with the VXDL language and managed by the HIPerNET framework

International audienceWith the convergence of computing and communication, and the expansion of cloud computing, new models and tools are needed to allow users to define, create, and exploit on-demand virtual infras- tructures within wide area distributed environments. Optimally design- ing customized virtual execution-infrastructure and executing them on a physical substrate remains a complex problem. This paper presents the VXDL language, a language for specifying and describing virtual infras- tructures and the HIPerNET framework to manage them. Based on the example of a specific biomedical application and workflow engine, this paper illustrates how VXDL enables to specify different customized vir- tual infrastructures and the HIPerNET framework to execute them on a distributed substrate. The paper presents experiments of the deploy- ment and execution of this application on different virtual infrastructures managed by our HIPerNet system. All the experiments are performed on the Grid'5000 testbed substrate

Neoproterozoic crustal evolution in Southern Chad: Pan-African ocean basin closing, arc accretion and late- to post-orogenic granitic intrusion.

International audienceIn the Lake Léré region, southern Chad, Neoproterozoic terrains are distributed in four lithostructural groups that reveal the geotectonic evolution of a part of the Pan-African orogenic domain. The first group includes basaltic volcanic rocks and fine-grained detrital sedimentary rocks of pre-tectonic basins that were emplaced in an extensional regime, close to a volcanic arc. The second and third groups include calc-alkaline gabbroic intrusions emplaced at an upper crustal level and a midcrustal tonalite, respectively, that are interpreted to be the roots of an active margin volcanic arc. These first three groups experienced WNW to ESE compression, and may belong to a fore-arc basic—volcanic arc—back-arc basin system that was accreted eastward to the Palaeoproterozoic Adamaoua-Yadé Block. The fourth group includes post-tectonic granite plutons invading the older groups. This paper documents the accretion processes in the southern margin of the Saharan Metacraton

Document d'aide au déploiement d'IPv6 sur Grid5000

Ce document présente succinctement les motivations pour l'utilisation d'IPv6 dans les grilles. Une analyse des opérations nécessaires pour son déploiement dans la plateforme Grid5000 est ensuite présentée et détaillée

Etude d'implémentations MPI dans une grille de calcul

National audienceThis paper presents an evaluation on the GRID'5000 platform of four MPI implementation: MPICH2, MPICH-Madeleine, OpenMPI et GridMPI. The comparison is based on a simple pingpong and the NAS parallel benchmarks. We show that GridMPI has the best results with regards to performances on the Grid if the implementation is well tuned. This paper details which parameters should be tuned.De nos jours, les grappes de PC ou clusters sont souvent interconnectés par des réseaux longue-distance de manière à former une grille afin d'offrir à un grand nombre d'utilisateurs un nombre plus conséquent de ressources. MPI, la bibliothèque de communication la plus utilisée pour les applications parallèles, a été efficacement implémentée dans un contexte de clusters. Deux caractéristiques des grilles, les réseaux longue-distance et l'hétérogénéité des processeurs et des réseaux, posent la question de l'efficacité de MPI sur les grilles. Cet article présente une évaluation sur la grille de recherche française GRID'5000, de 4 implémentations récentes de MPI : MPICH2, MPICH-Madeleine, OpenMPI et GridMPI. La comparaison est basée sur un pingpong, les NAS Parallel Benchmarks. Nous mettons en évidence les différences de performance obtenues avec les 4 implé- mentations. GridMPI montre les meilleures performances. L'exécution d'applications MPI sur la grille peut être bénéfique à condition de régler finement certains paramètres des implémentations. Cet article détaille les para- mètres mis en jeu et leurs réglages