De: HPCC 2014 Objet: HPCC 2014 notification for paper 121 Date: 26 juin 2014 15:24:40 UTC+2 À: David Laiymani Dear David Laiymani, On behalf of the Program Committee of HPCC 2014, we would like to inform you that the paper titled:Simulation of Asynchronous Iterative Algorithms Using SimGrid(paper ID number 121) has not been accepted for presentation at the main track of the conference but due to its quality, your paper is accepted in the associated Workshops of the HPCC2014 conference, and will be published in the same proceedings by IEEE CPS and indexed in IEEE Xplorer. Please modify your paper according to the instructions and comments provided by the reviewers. Please prepare and submit your final camera ready paper and follow all STEPs to ensure the submission process is completed successfully. Please note Camera ready submission deadline is 15 July 2014. Authors must follow the IEEE formatting instruction. For further information please check: www.computational-science.org/HPCC2014 We are looking forward to meeting you at the HPCC 2014 conference. S. Khaddaj, Program Chair of HPCC 2014 J. Bourgeois, General Chair of HPCC2014 F. Magoules, General Chair of HPCC2014 ----------------------- REVIEW 1 --------------------- PAPER: 121 TITLE: Simulation of Asynchronous Iterative Algorithms Using SimGrid AUTHORS: Charles Emile Ramamonjisoa, David Laiymani, Arnaud Giersch, Lilia Ziane Khodja and Raphaël Couturier ----------- REVIEW ----------- The contribution of the paper could be better described. The authors state that: "we show that SimGrid is an efficient simulation tool that has enabled .." If this is one of the goals of the paper to present the capabilities/strength of SimGrid, then they should compare it with other tools for the comparison of the two methods. Regarding the comparison of the two methods, the possible scalability expected in the case of larger platforms might also be commended / discussed. ----------------------- REVIEW 2 --------------------- PAPER: 121 TITLE: Simulation of Asynchronous Iterative Algorithms Using SimGrid AUTHORS: Charles Emile Ramamonjisoa, David Laiymani, Arnaud Giersch, Lilia Ziane Khodja and Raphaël Couturier ----------- REVIEW ----------- This paper describes the simulation of an adapted (authors say slightly changed) GMRES solver on the SimGrid simulation framework; the GMRES solver is changed from synchronous iterative solution to a asynchronous iteration scheme in order to overcome latencies when interconnecting computers in a Grid environment. The prejudice of the paper is that the GMRES algorithm is not using non-blocking communication to begin with. You mention that for running with SimGrid using SMPI, "little" or no modification need to be done to the original code: what kind of modifications are necessary -- and did You have to apply any modification to run with SMPI? (in a later section of the paper, changing / deleting global variables were mentioned -- due to the threaded execution of simulated MPI processes...) SimGrid uses a "fluid model" -- what does that mean? The local convergence criterion (k<=MaxIter) seams wrong and should rather read: k == MaxIter? As far as the reviewer can tell, SMPI removes heavy computation by making assumptions on the CPU performance of the simulated code -- which however is not true with most Grid environments where You do have mixed architectures and mixed performance characteristics. How is this handled? However, the main gripe about this paper is the rather unrealistic assumption on bandwidth (5 Mbps!) and latency (20ms): the internal network of a cluster may be Infiniband, with bw of Gigabytes/sec and micro-second latency, while a second cluster may be reachable over Gigabit-Ethernet with 100-200x the latency... This would be a setup, where a (even slight) gain would provide more convincing results. Some knitpicks include: - Abstract: "Behaviours", please no plural - Sec II (and others): "As exposed" --> "As described" - Sec II: "And important idle times" --> better "useless idle times used for synchronization" - Sec III: "by the mean of an XML file" --> "by means of an XML file". - SEC IV.B: did not encouter ... unless some code debugging" --> please rewrite the unless part... - SEC V: "Hosts processors power" --> "Host processor power" ----------------------- REVIEW 3 --------------------- PAPER: 121 TITLE: Simulation of Asynchronous Iterative Algorithms Using SimGrid AUTHORS: Charles Emile Ramamonjisoa, David Laiymani, Arnaud Giersch, Lilia Ziane Khodja and Raphaël Couturier ----------- REVIEW ----------- The submitted paper purports to be the first simulation of asynchronous iterative algorithms and predicts that, for a particular cluster configurations with very high latency (20ms) and very low bandwidths (5/50 Mbit/s), an unpreconditioned asynchronous multisplitting algorithm will be faster than an unpreconditioned GMRES algorithm for solving a 3D Poisson equation. Several issues with respect to the relevance of these results deserve discussion: 1) There is no substantial discussion of the fundamental additions to SimGrid that were required in order to support the simulation of asynchronous iterative algorithms. If no extensions were required, then I am unsure as to how this aspect of the work is a contribution. 2) The model problem of a 3D Poisson equation with no preconditioner is regrettable due to the large number of fast solvers available that have been available for many decades. For this reason, as is, the results are not relevant to the solution of PDEs. However, a similar computational structure appears within the context of gradient descent methods for the solution of convex optimization problems, and asynchronous algorithms are quite common. I would humbly suggest such a model problem in the future unless either a more challenging PDE is tackled or a non-trivial preconditioner is incorporated. 3) This is somewhat of a minor point, but I did not see an explicit discussion of the link between a global relative residual norm, || A x - b|| / || b ||, and the local convergence criterion used in the asynchronous algorithm, which tested for the infinity norm of the local computation. When "precision" is reported in Table I, is it referring to a consistent global convergence criterion? And, if so, what is it precisely referring to? 4) Typical latencies within clusters are on the order of a microsecond, and the latency used to produce Table I is more than three orders of magnitude higher (20ms). It would be helpful if more justification was given for why such a high latency is relevant. Furthermore, the chosen bandwidths (5 Mbit/s and 50 Mbit/s) are closer to a non-commercial home internet connection than a commercial ethernet connection. Overall, I feel that a significant number of issues should be addressed before publication would be warranted. ----------------------- REVIEW 4 --------------------- PAPER: 121 TITLE: Simulation of Asynchronous Iterative Algorithms Using SimGrid AUTHORS: Charles Emile Ramamonjisoa, David Laiymani, Arnaud Giersch, Lilia Ziane Khodja and Raphaël Couturier ----------- REVIEW ----------- This is a very interesting paper devoted to the implementation in a grid environment of some asynchronous algorithm. These algorithms are indeed very powerfull, and the more latency, the more efficient are these algorithms. A comparison of a synchronous GMRES and an asynchronous multi-splitting is presented. The obtained results are interesting and confirm the efficiency of these methods. ----------------------- REVIEW 5 --------------------- PAPER: 121 TITLE: Simulation of Asynchronous Iterative Algorithms Using SimGrid AUTHORS: Charles Emile Ramamonjisoa, David Laiymani, Arnaud Giersch, Lilia Ziane Khodja and Raphaël Couturier ----------- REVIEW ----------- This paper is a mix between a short and a long paper, it presents preliminary works on simulation of asynchronous iterative algorithms using SimGrid. I recommend to accept it as a short paper.