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\section publications Publications \subsection simulation About simulation \li Scheduling Distributed Applications: the SimGrid Simulation Framework\n by Henri Casanova and Arnaud Legrand and Loris Marchal\n Proceedings of the third IEEE International Symposium on Cluster Computing and the Grid (CCGrid'03)\n Since the advent of distributed computer systems an active field of research has been the investigation of scheduling strategies for parallel applications. The common approach is to employ scheduling heuristics that approximate an optimal schedule. Unfortunately, it is often impossible to obtain analytical results to compare the efficacy of these heuristics. One possibility is to conducts large numbers of back-to-back experiments on real platforms. While this is possible on tightly-coupled platforms, it is infeasible on modern distributed platforms (i.e. Grids) as it is labor-intensive and does not enable repeatable results. The solution is to resort to simulations. Simulations not only enables repeatable results but also make it possible to explore wide ranges of platform and application scenarios.\n In this paper we present the SimGrid framework which enables the simulation of distributed applications in distributed computing environments for the specific purpose of developing and evaluating scheduling algorithms. This paper focuses on SimGrid v2, which greatly improves on the first version of the software with more realistic network models and topologies. SimGrid v2 also enables the simulation of distributed scheduling agents, which has become critical for current scheduling research in large-scale platforms. After describing and validating these features, we present a case study by which we demonstrate the usefulness of SimGrid for conducting scheduling research. \li A Network Model for Simulation of Grid Application\n by Henri Casanova and Loris Marchal\n \anchor paper_tcp In this work we investigate network models that can be potentially employed in the simulation of scheduling algorithms for distributed computing applications. We seek to develop a model of TCP communication which is both high-level and realistic. Previous research works show that accurate and global modeling of wide-area networks, such as the Internet, faces a number of challenging issues. However, some global models of fairness and bandwidth-sharing exist, and can be link withthe behavior of TCP. Using both previous results and simulation (with NS), we attempt to understand the macroscopic behavior of TCP communications. We then propose a global model of the network for the Grid platform. We perform partial validation of this model in simulation. The model leads to an algorithm for computing bandwidth-sharing. This algorithm can then be implemented as part of Grid application simulations. We provide such an implementation for the SimGrid simulation toolkit.\n ftp://ftp.ens-lyon.fr/pub/LIP/Rapports/RR/RR2002/RR2002-40.ps.gz \li MetaSimGrid : Towards realistic scheduling simulation of distributed applications\n by Arnaud Legrand and Julien Lerouge\n Most scheduling problems are already hard on homogeneous platforms, they become quite intractable in an heterogeneous framework such as a metacomputing grid. In the best cases, a guaranteed heuristic can be found, but most of the time, it is not possible. Real experiments or simulations are often involved to test or to compare heuristics. However, on a distributed heterogeneous platform, such experiments are technically difficult to drive, because of the genuine instability of the platform. It is almost impossible to guarantee that a platform which is not dedicated to the experiment, will remain exactly the same between two tests, thereby forbidding any meaningful comparison. Simulations are then used to replace real experiments, so as to ensure the reproducibility of measured data. A key issue is the possibility to run the simulations against a realistic environment. The main idea of trace-based simulation is to record the platform parameters today, and to simulate the algorithms tomorrow, against the recorded data: even though it is not the current load of the platform, it is realistic, because it represents a fair summary of what happened previously. A good example of a trace-based simulation tool is SimGrid, a toolkit providing a set of core abstractions and functionalities that can be used to easily build simulators for specific application domains and/or computing environment topologies. Nevertheless, SimGrid lacks a number of convenient features to craft simulations of a distributed application where scheduling decisions are not taken by a single process. Furthermore, modeling a complex platform by hand is fastidious for a few hosts and is almost impossible for a real grid. This report is a survey on simulation for scheduling evaluation purposes and present MetaSimGrid, a simulator built on top of SimGrid.\n ftp://ftp.ens-lyon.fr/pub/LIP/Rapports/RR/RR2002/RR2002-28.ps.gz \li SimGrid: A Toolkit for the Simulation of Application Scheduling\n by Henri Casanova\n Advances in hardware and software technologies have made it possible to deploy parallel applications over increasingly large sets of distributed resources. Consequently, the study of scheduling algorithms for such applications has been an active area of research. Given the nature of most scheduling problems one must resort to simulation to effectively evaluate and compare their efficacy over a wide range of scenarios. It has thus become necessary to simulate those algorithms for increasingly complex distributed, dynamic, heterogeneous environments. In this paper we present SimGrid, a simulation toolkit for the study of scheduling algorithms for distributed application. This paper gives the main concepts and models behind SimGrid, describes its API and highlights current implementation issues. We also give some experimental results and describe work that builds on SimGrid's functionalities.\n http://grail.sdsc.edu/papers/simgrid_ccgrid01.ps.gz \subsection research Papers using SimGrid results \li Optimal algorithms for scheduling divisible workloads on heterogeneous systems\n by Olivier Beaumont and Arnaud Legrand and Yves Robert\n In this paper, we discuss several algorithms for scheduling divisible loads on heterogeneous systems. Our main contributions are (i) new optimality results for single-round algorithms and (ii) the design of an asymptotically optimal multi-round algorithm. This multi-round algorithm automatically performs resource selection, a difficult task that was previously left to the user. Because it is periodic, it is simpler to implement, and more robust to changes in the speeds of processors or communication links. On the theoretical side, to the best of our knowledge, this is the first published result assessing the absolute performance of a multi-round algorithm. On the practical side, extensive simulations reveal that our multi-round algorithm outperforms existing solutions on a large variety of platforms, especially when the communication-to-computation ratio is not very high (the difficult case).\n ftp://ftp.ens-lyon.fr/pub/LIP/Rapports/RR/RR2002/RR2002-36.ps.gz \li On-line Parallel Tomography\n by Shava Smallen\n Masters Thesis, UCSD, May 2001 \li Applying Scheduling and Tuning to On-line Parallel Tomography \n by Shava Smallen, Henri Casanova, Francine Berman\n in Proceedings of Supercomputing 2001 \li Heuristics for Scheduling Parameter Sweep applications in Grid environments\n by Henri Casanova, Arnaud Legrand, Dmitrii Zagorodnov and Francine Berman\n in Proceedings of the 9th Heterogeneous Computing workshop (HCW'2000), pp349-363. */