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[hpcc2014.git] / hpcc2014_reviews.txt

De: HPCC 2014 <hpcc2014@easychair.org>
Objet: HPCC 2014 notification for paper 121
Date: 26 juin 2014 15:24:40 UTC+2
À: David Laiymani <david.laiymani@univ-fcomte.fr>

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.
`----

[RCE] L’objectif du papier n’est pas de comparer des outils de
      simulation et d’arriver à une conclusion sur la performance de
      Simgrid. Ce dernier a été choisi parmi d’autres pour effectuer
      la comparaison entre les 2 algorithmes en mode async sur un
      environnement de grille distribuée.

      On peut modifier la phrase comme suit : "we show that SimGrid is
      one of efficient simulation tool that has enabled .."


,----
| Regarding the comparison of the two methods, the possible scalability
| expected in the case of larger platforms might also be commended /
| discussed.
`----

[RCE] Je pense que ça a été commenté / discuté tout au long du papier
      cette montée en charge possible sur des plateformes plus
      larges. Même dans la conclusion, on a avancé que l’objectif est
      de réussir à faire tourner le programme sur une plateforme plus
      large (en terme de nombre de cœurs et de nombre de clusters)
      mais aussi de pouvoir résoudre des problèmes de plus grande
      taille.


----------------------- 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.
`----

[RCE] Non, ce n’est pas tout à fait ça : on veut comparer l’algo GMRES
      qui est executé en mode SYNC avec l’algo de multisplitting qui
      lui sera executé en mode ASYNC.

[LZK] Pas uniquement la comparaison !
      Par la simulation sur SimGrid (et la comparaison des deux algorithmes),
      on a montré que notre méthode est plus adaptée aux grilles distribuées. 
      En quelque sorte, on a bien modifié l'algorithme de GMRES pour l'adapter
      aux clusters distants. On a utilisé des itérations asynchrones pour
      recouvrir les communications par du calcul et le multisplittig pour
      réduire le volume total des communications. De toute façon, on ne pouvait
      pas appliquer les itérations asynchrones sur GMRES sans le multisplitting.
      On peut bien sûr utiliser ces deux techniques avec une autre méthode
      numérique de résolution comme solveur interne.  

,----
| The prejudice of the paper is that the GMRES algorithm is not using
| non-blocking communication to begin with.
`----

[RCE] Comme dit juste plus haut, effectivement GMRES est resté SYNC
      donc en mode de communication bloquant.


,----
| 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...)
`----

[RCE] Les changements “mineurs” apportés sur le code lors de
      l’exécution dans Simgrid/SMPI par rapport à un lancement sur un
      environnement réel (MPI) se résument aux deux points suivants :
      - Toutes les variables globales ont été ramenées dans un scope
        local aux fonctions. Cette modification a entraîné le
        changement des définitions synoptiques des fonctions pour
        prendre en compte les passages de variables.
      - La sequence MPI_ISend, MPI_Irecv and MPI_Waitall a pose aussi
        un problème en mode Async. Elle a été remplacée par une
        sequence de 6 Isend/Irecv/Wait à la place.
 
      On peut donc faire un renvoi à la Section III pour clarifier :
      « The SMPI interface implements about 80% of the MPI 2.0
        standard [?]  and supports applications written in C or
        Fortran, with little or no modifications. »
      On écrira :
      « The SMPI interface implements about 80% of the MPI 2.0
        standard [?]  and supports applications written in C or
        Fortran, with little or no modifications. (cf Section IV
        paragraph B) »


,----
| SimGrid uses a "fluid model" -- what does that mean?
`----

[RCE] Arnaud peut-il aider ici ?
 [AG] Je fais.

,----
| The local convergence criterion (k<=MaxIter) seams wrong and should
| rather read: k == MaxIter?
`----

[RCE] Je pense que le reviewer a raison. Lilia ?
[LZK] OUI, 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?
`----

[RCE] Simgrid/SMPI prévoit cette hétérogénéité des composants des
      clusters dans une grille par la définition plus ou moins fine
      des caractéristiques des nœuds composant les clusters (puissance
      CPU, mémoire RAM, …) d’une part mais aussi par la description
      plus ou moins détaillée aussi du réseau de communication entre
      les clusters de la grille.

,----
| 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.
`----

[RCE] Il faut qu’on précise que ces caractéristiques de réseau “non
      réalistes” concernent le réseau INTER cluster. Le réseau INTRA
      cluster sont bien dans l’ordre de grandeur donnée (Gbps de bw et
      ms de latence). Toutefois, le reviewer a bien vu qu’on a poussé
      trop fort sur le réseau inter-cluster ☺ Mais ce n’est qu’à ce
      prix qu’on a commencé à avoir un gain appréciable.



,----
| Some knitpicks include:
| [x] Abstract: "Behaviours", please no plural
| [x] Sec II (and others): "As exposed" --> "As described"
| [ ] Sec II: "And important idle times" --> better "useless idle times
|     used for synchronization"
| [x] 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...
| [x] SEC V: "Hosts processors power" --> "Host processor power"
`----

[RCE] On va prendre en compte ces remarques.
 [AG] J'ai commencé pour les plus faciles (cochées dans la liste ci-dessus).


----------------------- 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.
`----

[RCE] Il n’y avait pas d’extensions apportées à SIMGRID pour résoudre
      le type d’algorithme choisi.

,----
| 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.
`----

[RCE] ??
 

,----
| 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?
`----

[RCE] Selon ma comprehension, la “precision” de la table I est la
      “tolerance threshold” (epsilon) mentionnée dans la Section
      IV. Il permet effectivement de determiner le critère ou la
      condition de convergence globale. Lilia peut confirmer ?

[LZK] En asynchrone, on a toujours utilisé cette condition pour détecter
      la convergence. Pour la convergence du solveur GMRES sur chaque
      cluster (indépendemment de la convergence globale) on utilise ce
      critère: || A x - b|| / || b ||<=inner precision. Pour la convergence 
      globale, elle est détectée quand tous les calculs locaux ont 
      convergé: (k==MaxIter)or(X^k−X^k+1)<=epsilon, X sous-vecteur
      local de la solution et epsilon est la outer precision et donc
      la précision donnée dans la table I. 

,----
| 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.
`----

[RCE] Voir remarques plus haut.

,----
| 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.
`----

[RCE] Bien compris.


----------------------- 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.
`----