A Framework for Adaptive Collective Communications on Heterogeneous Hierarchical Networks

Extended version of the IPDPS 2006 paperToday, due to the wide variety of existing parallel systems consisting on collections of heterogeneous machines, it is very difficult for a user to solve a target problem by using a single algorithm or to write portable programs that perform well on multiple computational supports. The inherent heterogeneity and the diversity of networks of such environments represent a great challenge to model the communications for high performance computing applications. Our objective within this work is to propose a generic framework based on communication models and adaptive techniques for dealing with prediction of communication performances on cluster-based hierarchical platforms. Toward this goal, we introduce the concept of polyalgorithmic model of communications, which correspond to selection of the most adapted communication algorithms and scheduling strategies, giving the characteristics of the hardware resources of the target parallel system. We apply this methodology on collective communication operations and show that the framework provides significant performances while determining the best algorithm depending on the problem and architecture parameters

Modeling Network Contention Effects on All-to-All Operations

10 pagesOne of the most important collective communication patterns used in scientific applications is the complete exchange, also called All-to-All. Although efficient complete exchange algorithms have been studied for specific networks, general solutions like those available in well-known MPI distributions (e.g. the MPI_Alltoall operation) are strongly influenced by the congestion of network resources. In this paper we present an integrated approach to model the performance of the All-to-All collective operation. Our approach consists in identifying a contention signature that characterizes a given network environment, using it to augment a contention-free communication model. This approach allows an accurate prediction of the performance of the All-to-All operation over different network architectures with a small overhead. This approach is assessed by experimental results using three different network architectures, namely Fast Ethernet, Gigabit Ethernet and Myrinet

Fast and Scalable Total Order Broadcast for Wide-area Networks

Version submitted to IEEE TPDSFault tolerant protocols such as Total Order Broadcast are key aspects on the development of reliable distributed systems, but they are barely supported on large-scale systems due to the cost of traditional techniques. This paper revisits a class of Total Order Broadcast protocols called moving sequencer, known by its communication efficiency. Indeed, we evaluate RBP, one of the most known implementations of moving sequencer protocols. We demonstrate how RBP can be used with wide-area systems, and we propose new techiques to improve its resiliency and consistency properties under failures, as well as improving its scalability aspects

Modelling Network Contention Effects\\ on All-to-All Operations

version étendue de l'article publié à CLUSTER2006One of the most important collective communication patterns used in scientific applications is the complete exchange, also called All-to-All. Although efficient complete exchange algorithms have been studied for specific networks, general solutions like those available in well-known MPI distributions (e.g. the MPI_Alltoall operation) are strongly influenced by the congestion of network resources. In this paper we present an integrated approach to model the performance of the All-to-All collective operation. Our approach consists in identifying a contention signature that characterizes a given network environment, using it to augment a contention-free communication model. This approach allows an accurate prediction of the performance of the All-to-All operation over different network architectures with a small overhead. This approach is assessed by experimental results using three different network architectures, namely Fast Ethernet, Gigabit Ethernet and Myrinet

Strong Consistency for Shared Objects in Pervasive Grids

International audienceRecent advances in communication technology en- able the emergence of a new generation of applications that integrates mobile devices with classical high performance systems as part of a common computing environment. In such environ- ments, keeping the coherence of shared data (distributed objects, for example) represents a real challenge as communications are strongly influenced by the performance and the reliability of mobile devices (laptops, PDAs and cellular telephones) and wireless networks (WiFi, Bluetooth). Indeed, data incoherence may arise due to message losses or node volatility, which blocks the algorithms used to synchronize these data. In this paper, we analyze the main challenges concerning the manipulation of shared distributed objects in a pervasive environment. We demonstrate how a membership service can be enhanced to tolerate temporary disconnections and message losses without blocking, while reducing the number of exchanged message

A framework for adaptive collective communications for heterogeneous hierarchical computing systems

Collective communication operations are widely used in MPI applications and play an important role in their performance. However, the network heterogeneity inherent to grid environments represent a great challenge to develop efficient high performance computing applications. In this work we propose a generic framework based on communication models and adaptive techniques for dealing with collective communication patterns on grid platforms. Toward this goal, we address the hierarchical organization of the grid, selecting the most efficient communication algorithms at each network level. Our framework is also adaptive to grid load dynamics since it considers transient network characteristics for dividing the nodes into clusters. Our experiments with the broadcast operation on a real-grid setup indicate that an adaptive framework allows significant performance improvements on MPI collective communications

Total Exchange Performance Prediction on Grid Environments: modeling and algorithmic issues

ISBN 978-0-387-72497-3 (Print) 978-0-387-72498-0 (Online) Copyright : 2008International audienceOne of the most important collective communication patterns used in scientific applications is the complete exchange, also called All-to-All. Although efficient algorithms have been studied for specific networks, general solutions like those available in well-known MPI distributions (e.g. the MPI Alltoall operation) are strongly influenced by the congestion of network resources. In this paper we address the problem of modeling the performance of Total Exchange communication operations in grid environments. Because traditional performance models are unable to predict the real completion time of an All-to-All operation, we try to cope with this problem by identifying the factors that can interfere in both local and distant transmissions. We observe that the traditional MPI Alltoall implementation is not suited for grid environments, as it is both inefficient and hard to model. We focus therefore in an alternative algorithm for the total exchange redistribution problem. In our approach we perform communications in two different phases, aiming to minimize the number of communication steps through the wide-area network. This reduction has a direct impact on the performance modeling of the MPI Alltoall operation, as we minimize the factors that interfere with wide-area communications. Hence, we are able to define an accurate performance modeling of a total exchange between two clusters

A new heuristic for broadcasting in clusters of clusters

International audienceThis paper deals with the problem of broadcasting for clus- ter of clusters. The construction of partial minimum spanning trees being NP-complete, several heuristic algorithms have been already formulated. Many of these heuristics (like the heuristic of Kruskal) use the shortest path to connect the components of the tree. They are not relevant in case of forwarding or overlapping communication during a step of the algorithm. In this paper, we study a new heuristic for the minimum broadcasting tree and we evaluate it through simulations with different communication parameters and also through real experimentation over the Grid'5000 testbed

Analyse des mécanismes de découverte de services avec prise en charge du contexte et de l'intention

National audienceAvec la démocratisation des dispositifs et des réseaux mobiles, les systèmes d'information deviennent pervasifs. Les utilisateurs de ces systèmes doivent désormais évoluer dans de véritables espaces de services, dans lesquels plusieurs services sont offerts. Afin d'améliorer la transparence des systèmes d'information pervasifs, nous proposons une nouvelle approche pour ces systèmes, à la fois sensible au contexte et intentionnelle. Dans cette approche, les services offerts par ces systèmes sont proposés afin de satisfaire à une intention, laquelle correspond à l'expression d'un but utilisateur, dans un contexte donné. Pour valider cette approche, nous développons actuellement une plate-forme de découverte de services basée sur une extension de OWL-S qui intègre ces notions. Grâce à des résultats expérimentaux, nous analysons l'impact de l'usage de ces notions de contexte et d'intention dans la sélection de services et démontrons l'intérêt de notre approche dans la découverte des services

Service Discovery Mechanism for an Intentional Pervasive Information System

International audiencePervasive Information System (PIS) provides a new vision of Information System available anytime and anywhere. The users of these systems must evolve in a space of services, in which several services are offered to him. However, PIS should enhance the transparency and efficiency of the system. We believe that a user-centric vision is needed to ensure a transparent access to the frequently changing space of services regardless of how to perform it. In this paper, we propose a new approach of PIS, both context-aware and intentional called IPIS. In this approach, services are proposed in order to satisfy user's intention in a given context. Then, we propose a context-aware intentional service discovery mechanism. Such mechanism is based on an extension of OWL-S taking into account the notion of context and intention. We present in this paper IPIS platform. Then, we detail the proposed service discovery mechanism and present experimental results that demonstrate the advantage of using our proposition