X-Git-Url: https://bilbo.iut-bm.univ-fcomte.fr/and/gitweb/rce2015.git/blobdiff_plain/6b22d1f20898ec19053d9010bbf500f86df50b13..22a9813bcf12424913d9b03c1687a0b07f7a5516:/paper.tex?ds=sidebyside diff --git a/paper.tex b/paper.tex index 95683d5..31e2676 100644 --- a/paper.tex +++ b/paper.tex @@ -317,10 +317,12 @@ suppress all global variables by replacing them with local variables or using a Simgrid selector called "runtime automatic switching" (smpi/privatize\_global\_variables). Indeed, global variables can generate side effects on runtime between the threads running in the same process, generated by -the Simgrid to simulate the grid environment. \RC{On vire cette phrase ?}The -last modification on the MPI program pointed out for some cases, the review of -the sequence of the MPI\_Isend, MPI\_Irecv and MPI\_Waitall instructions which -might cause an infinite loop. +Simgrid to simulate the grid environment. + +%\RC{On vire cette phrase ?} \RCE {Si c'est la phrase d'avant sur les threads, je pense qu'on peut la retenir car c'est l'explication du pourquoi Simgrid n'aime pas les variables globales. Si c'est pas bien dit, on peut la reformuler. Si c'est la phrase ci-apres, effectivement, on peut la virer si elle preterais a discussion}The +%last modification on the MPI program pointed out for some cases, the review of +%the sequence of the MPI\_Isend, MPI\_Irecv and MPI\_Waitall instructions which +%might cause an infinite loop. \paragraph{Simgrid Simulator parameters} @@ -343,9 +345,16 @@ In addition, the following arguments are given to the programs at runtime: \begin{itemize} \item maximum number of inner and outer iterations; \item inner and outer precisions; - \item matrix size (N$_{x}$, N$_{y}$ and N$_{z}$); - \item matrix diagonal value = 6.0 (for synchronous Krylov multisplitting experiments and 6.2 for asynchronous block Jacobi experiments); \RC{CE tu vérifies, je dis ca de tête} - \item execution mode: synchronous or asynchronous. + \item maximum number of the gmres's restarts in the Arnorldi process; + \item maximum number of iterations qnd the tolerance threshold in classical GMRES; + \item tolerance threshold for outer and inner-iterations; + \item matrix size (N$_{x}$, N$_{y}$ and N$_{z}$) respectively on x, y, z axis; + \item matrix diagonal value = 6.0 for synchronous Krylov multisplitting experiments and 6.2 for asynchronous block Jacobi experiments; \RC{CE tu vérifies, je dis ca de tête} + \item matrix off-diagonal value; + \item execution mode: synchronous or asynchronous; + \RCE {C'est ok la liste des arguments du programme mais si Lilia ou toi pouvez preciser pour les arguments pour CGLS ci dessous} \RC{Vu que tu n'as pas fait varier ce paramètre, on peut ne pas en parler} + \item Size of matrix S; + \item Maximum number of iterations and tolerance threshold for CGLS. \end{itemize} It should also be noticed that both solvers have been executed with the Simgrid selector -cfg=smpi/running\_power which determines the computational power (here 19GFlops) of the simulator host machine. @@ -356,7 +365,10 @@ It should also be noticed that both solvers have been executed with the Simgrid \section{Experimental Results} \label{sec:expe} -In this section, experiments for both Multisplitting algorithms are reported. First the problem sued in our experiments is described. +In this section, experiments for both Multisplitting algorithms are reported. First the 3D Poisson problem used in our experiments is described. + +\subsection{3D Poisson} + We use our two-stage algorithms to solve the well-known Poisson problem $\nabla^2\phi=f$~\cite{Polyanin01}. In three-dimensional Cartesian coordinates in $\mathbb{R}^3$, the problem takes the following form \begin{equation} @@ -393,7 +405,7 @@ have been chosen for the study in this paper. \\ \textbf{Step 2}: Collect the software materials needed for the experimentation. In our case, we have two variants algorithms for the resolution of the 3D-Poisson problem: (1) using the classical GMRES; (2) and the Multisplitting method. In addition, the Simgrid simulator has been chosen to simulate the behaviors of the -distributed applications. Simgrid is running on the Mesocentre datacenter in the University of Franche-Comte and also in a virtual machine on a laptop. \\ +distributed applications. Simgrid is running on the Mesocentre datacenter in the University of Franche-Comte and also in a virtual machine on a simple laptop. \\ \textbf{Step 3}: Fix the criteria which will be used for the future results comparison and analysis. In the scope of this study, we retain @@ -445,35 +457,32 @@ transit between the clusters and nodes during the code execution. In a grid environment, it is common to distinguish, on the one hand, the "intra-network" which refers to the links between nodes within a cluster and, on the other hand, the "inter-network" which is the backbone link between - clusters. In practse; these two networks have different speeds. The + clusters. In practice, these two networks have different speeds. The intra-network generally works like a high speed local network with a high bandwith and very low latency. In opposite, the inter-network connects clusters sometime via heterogeneous networks components throuth internet with a lower speed. The network between distant clusters might be a bottleneck for the global performance of the application. -\subsection{Comparing GMRES and Multisplitting algorithms in +\subsection{Comparison of GMRES and Krylov Multisplitting algorithms in synchronous mode} -In the scope of this paper, our first objective is to demonstrate the -Algo-2 (Multisplitting method) shows a better performance in grid -architecture compared with Algo-1 (Classical GMRES) both running in -\textit{synchronous mode}. Better algorithm performance -should means a less number of iterations output and a less execution time -before reaching the convergence. For a systematic study, the experiments -should figure out that, for various grid parameters values, the -simulator will confirm the targeted outcomes, particularly for poor and -slow networks, focusing on the impact on the communication performance -on the chosen class of algorithm. +In the scope of this paper, our first objective is to analyze when the Krylov +Multisplitting method has better performances than the classical GMRES +method. With an iterative method, better performances mean a smaller number of +iterations and execution time before reaching the convergence. For a systematic +study, the experiments should figure out that, for various grid parameters +values, the simulator will confirm the targeted outcomes, particularly for poor +and slow networks, focusing on the impact on the communication performance on +the chosen class of algorithm. The following paragraphs present the test conditions, the output results and our comments.\\ -\textit{3.a Executing the algorithms on various computational grid +\subsubsection{Execution of the the algorithms on various computational grid architecture and scaling up the input matrix size} -\\ - +\ \\ % environment \begin{footnotesize} \begin{tabular}{r c }