Deep redshift topological lensing: strategies for the T^3 candidate

The 3-torus (T^3) FLRW model better fits the nearly zero large-scale auto-correlation of the WMAP CMB sky maps than the infinite flat model. The T^3 model's WMAP parameters imply approximately equal-redshift topological lensing at z \sim 6. We investigate observational strategies for rejecting the T^3 solution or providing candidate topologically lensed galaxy pairs. T^3 holonomies are applied to (i) existing z \sim 6 observations and (ii) simulated observations, creating multiply connected catalogues. Corresponding simply connected catalogues are generated. Each catalogue is analysed using a successive filter method and collecting matched quadruples. Quadruple statistics between the multiply and simply connected catalogues are compared. The expected rejection of the hypothesis, or detection of candidate topologically lensed galaxies, is possible at a significance of 5% for a pair of T^3 axis-centred northern and southern surveys if photometric redshift accuracy is \sigma(\zphot) < 0.01 for a pair of nearly complete 100 deg^2 surveys with a total of > 500 galaxies over 4.3 < z < 6.6, or for a pair of 196 deg^2 surveys with > 400 galaxies and \sigma(\zphot) < 0.02 over 4<z<7. Dropping the maximum time interval in a pair from \Delta t =1 Gyr/h to \Delta t =0.1 Gyr/h yields a requirement of \sigma(\zphot) < 0.005 or \sigma(\zphot) < 0.01, respectively. Millions of z \sim 6 galaxies will be observed over fields of these sizes during the coming decades, implying much stronger constraints. The question is not if the hypothesis will be rejected or confirmed, it is when.Comment: 13 pages, 9 figures, 5 tables, MNRAS, accepte

Orchestration d'expériences à l'aide de processus métier

National audienceLa recherche sur les systèmes distribués a quelques caractéristiques qui la rende intéressante, difficile et unique. D'abord, les systèmes modernes sont souvent trop compliqués pour permettre une analyse formelle et théorique. Ainsi, l'approche la plus courante est l'analyse empirique, par exemple à l'aide d'expériences. Malheureusement, à cause de la complexité des systèmes informatiques, réaliser des expériences est très difficile à faire correctement, avec une rigueur scientifique suffisante et de façon reproductible. Cet article présente une idée novatrice pour écrire, représenter et conduire les expériences scientifiques impliquant une multitude des noeuds hétérogènes connectés par un réseau. L'idée centrale consiste à utiliser la modélisation et le pilotage de processus métier (Business Process Modeling et Business Process Management). Notre solution a de nombreux avantages, dont les plus importants sont la facilité d'écrire et de comprendre une description d'expérience, et la robustesse d'exécution d'expériences même en présence de problèmes de traitement. Après la présentation de notre approche, un prototype du moteur de conduite d'expériences est validé à l'aide d'un cas d'utilisation de référence

Accurate emulation of CPU performance

This paper addresses the question of CPU performance emulation, which allows experimenters to evaluate applications under a wide range of reproducible experimental conditions. Specifically, we propose Fracas, a CPU emulator that leverages the Linux Completely Fair Scheduler to achieve performance emulation of homogeneous or heterogeneous multi-core systems. Several benchmarks reproducing different types of workload (CPU-bound, IO-bound) are then used to thoroughly compare Fracas with another CPU emulator and hardware frequency scaling. We show that the design of Fracas results in a more accurate and a less intrusive CPU emulation solution

A survey of general-purpose experiment management tools for distributed systems

International audienceIn the field of large-scale distributed systems, experimentation is particularly difficult. The studied systems are complex, often nondeterministic and unreliable, software is plagued with bugs, whereas the experiment workflows are unclear and hard to reproduce. These obstacles led many independent researchers to design tools to control their experiments, boost productivity and improve quality of scientific results. Despite much research in the domain of distributed systems experiment management, the current fragmentation of efforts asks for a general analysis. We therefore propose to build a framework to uncover missing functionality of these tools, enable meaningful comparisons be-tween them and find recommendations for future improvements and research. The contribution in this paper is twofold. First, we provide an extensive list of features offered by general-purpose experiment management tools dedicated to distributed systems research on real platforms. We then use it to assess existing solutions and compare them, outlining possible future paths for improvements

Using business workflows to improve quality of experiments in distributed systems research

International audienceDistributed systems pose many difficult problems to researchers. Due to their large-scale complexity, their numerous constituents (e.g., computing nodes, network links) tend to fail in unpredictable ways. This particular fragility of experiment execution threatens reproducibility, often considered to be a foundation of experimental science. Our poster presents a new approach to description and execution of experiments involving large-scale computer installations. The main idea consists in describing the experiment as workflow and using achievements of Business Workflow Management to reliably and efficiently execute it. Moreover, to facilitate the design process, the framework provides abstractions that hide unnecessary complexity from the user

Leveraging business workflows in distributed systems research for the orchestration of reproducible and scalable experiments

National audienceWhile rapid research on distributed systems is observed, experiments in this field are often difficult to design, describe, conduct and reproduce. By overcoming these difficulties the research could be further stimulated and add more credibility to results in distributed systems research. The key factors responsible for this situation are technical (software bugs and hardware errors), methodological (incorrect practices), as well as social (reluctance to share work). In this paper, the existing approaches for the management of experiments on distributed systems are described and a novel approach using business process management (BPM) is presented to address their shortcomings. Then, the questions arising when such approach is taken, are addressed. We show that it can be a better alternative to the traditional way of performing experiments as it encourages better scientific practices and results in more valuable research and publications. Finally, a plan of our future work is outlined and other applications of this work are discussed.Malgré une activité de recherche sur les systèmes distribués très importante et très active, les expériences dans ce domaine sont souvent difficiles à concevoir, décrire, mener et reproduire. Surmonter ces difficultés pourrait permettre à ce domaine d'être encore plus stimulé, et aux résultats de gagner en crédibilité, à la fois dans le domaine des systèmes distribués. Les facteurs principaux responsables de cette situation sont techniques (bugs logiciels, problèmes matériels), méthodologiques (mauvaises pratiques), et sociaux (réticence à partager son travail). Dans cet article, les approches existantes pour la description et la conduite d'expériences sur les systèmes distribués sont décrites, et une nouvelle approche, utilisant le \textsl{Business Process Management (BPM)}, est présentée pour répondre à leurs limitations. Puis diverses questions se posant lors de l'utilisation d'une telle approche sont discutées. Nous montrons que cette approche peut être une meilleure alternative à la manière traditionnelle de conduire des expériences, qui encourage de meilleures pratiques scientifiques, et qui résulte en une recherche et des publications de meilleure qualité. Pour finir, notre plan de travail est décrit, et des applications possibles de ce travail dans d'autres domaines sont décrites

Accurate emulation of CPU performance

International audienceThis paper addresses the question of CPU performance emulation, which allows experimenters to evaluate applications under a wide range of reproducible experimental conditions. Specifically, we propose Fracas, a CPU emulator that leverages the Linux Completely Fair Scheduler to achieve performance emulation of homogeneous or heterogeneous multi-core systems. Several benchmarks reproducing different types of workload (CPU-bound, IO-bound) are then used to thoroughly compare Fracas with another CPU emulator and hardware frequency scaling. We show that the design of Fracas results in a more accurate and a less intrusive CPU emulation solution.Cet article s'intéresse à la question de l'émulation de la performance du processeur, afin de permettre aux expérimenteurs d'évaluer des applications sous un large intervalle de conditions experimentales. Plus précisément, nous proposons Fracas, un émulateur de processeur qui utilise le Linux Completely Fair Scheduler pour obtenir une émulation des performances de machines multi-coeurs homogènes ou hétérogènes. Plusieurs benchmarks, reproduisant différents types de charge (CPU-intensif, I/O-intensif) sont ensuite utilisés pour comparer de manière extensive Fracas avec un autre émulateur, et avec le réglage matériel de la fréquence du processeur. Nous montrons que la conception de Fracas résulte en une émulation plus précise et moins intrusive

Emulation at Very Large Scale with Distem

International audienceProspective exascale systems and large-scale cloud infrastructures are composed of dozens of thousands of nodes. Evaluating applications that target such environments is extremely difficult. In this paper, we present an extension of the Distem emulator to allow experimenting on very large scale emulated platforms thanks to the use of a VXLAN overlay network. We demonstrate that Distem is capable of emulating 40,000 virtual nodes on 168 physical nodes, and use the resulting emulated environment to compare two efficient parallel command runners: TakTuk and ClusterShell

Methods for Emulation of Multi-Core CPU Performance

International audienceWhen validating or evaluating real distributed applications, it is useful to be able to test the application in a large range of environments. In that context, emulation of CPU performance enables researchers to investigate how the performance of the application is affected by the performance of the participating CPUs. Using a homogeneous cluster of fast multi-core nodes, it is therefore possible to evaluate how an application would behave on a heterogeneous set of nodes, with varying performance and number of cores. In this paper, three new methods for the emulation of CPU performance in the multi-core case are proposed: Fracas, CPU-Gov, and CPU-Hogs. Fracas relies on smart configuration of the Linux scheduler to achieve the desired emulation, CPU-Gov leverages the hardware CPU frequency scaling, and CPU-Hogs is a multi-core implementation of a CPU burner. These methods are compared and evaluated together with existing methods, with a set of micro-benchmarks, and show significant improvements over state-of-the-art solutions.Lors de la validation ou de l'évaluation d'applications distribuées, il est important de pouvoir tester l'application dans un large intervalle d'environnements expérimentaux. Dans ce contexte, l'émulation de la performance du processeur permet aux expérimenteurs d'évaluer comment la performance de l'application est affectée par la performance des processeurs utilisés. Tout en utilisant un ensemble homogène de machines multi-coeurs, il est ainsi possible d'évaluer l'application sur un ensemble de machines hétérogène, en faisant varier la performance et le nombre de coeurs. Dans cet article, trois nouvelles méthodes pour l'émulation de la performance de processeurs multi-coeurs sont proposées: Fracas, CPU-Gov, et CPU-Hogs. Fracas configure l'ordonnanceur de Linux pour atteindre les paramètres d'émulation souhaités, CPU-Gov utile le support matériel pour le changement de fréquence processeur, et CPU-Hogs est une implémentation d'un brûleur de processeur en multi-coeur. Ces méthodes sont comparées et évaluées avec des méthodes existantes à l'aide d'une suite de benchmarks, et montrent des améliorations significatives par rapport à l'état de l'art

Towards Complete Tracking of Provenance in Experimental Distributed Systems Research

International audienceRunning experiments on modern systems like supercomput-ers, cloud infrastructures or P2P networks became very complex, both technically and methodologically. It is difficult to rerun an experiment or understand its results even with technical background on the technology and methods used. Storing the provenance of experimental data, i.e., storing information about how the results were produced, proved to be a powerful tool to address similar problems in computational natural sciences. In this paper, we (1) survey provenance collection in various domains of computer science, (2) introduce a new classification of prove-nance types, and (3) sketch a design of a provenance system inspired by this classification