From: David Laiymani Date: Wed, 6 May 2015 14:24:03 +0000 (+0200) Subject: Merge branch 'master' of ssh://bilbo.iut-bm.univ-fcomte.fr/rce2015 X-Git-Url: https://bilbo.iut-bm.univ-fcomte.fr/and/gitweb/rce2015.git/commitdiff_plain/cb07dd536bdfe2ca24b31fdd3d95195cde19513b?ds=inline;hp=-c Merge branch 'master' of ssh://bilbo.iut-bm.univ-fcomte.fr/rce2015 --- cb07dd536bdfe2ca24b31fdd3d95195cde19513b diff --combined paper.tex index 42f4b5d,1f9b49c..c198158 --- a/paper.tex +++ b/paper.tex @@@ -465,19 -465,19 +465,19 @@@ and between distant clusters. This p 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. +method. With a synchronous 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.\\ -\subsubsection{Execution of the the algorithms on various computational grid -architecture and scaling up the input matrix size} +\subsubsection{Execution of the algorithms on various computational grid +architectures and scaling up the input matrix size} \ \\ % environment @@@ -501,9 -501,9 +501,9 @@@ In this section, we analyze the performences of algorithms running on various -grid configuration (2x16, 4x8, 4x16 and 8x8). First, the results in Figure~\ref{fig:01} -show for all grid configuration the non-variation of the number of iterations of -classical GMRES for a given input matrix size; it is not the case for the +grid configurations (2x16, 4x8, 4x16 and 8x8). First, the results in Figure~\ref{fig:01} +show for all grid configurations the non-variation of the number of iterations of +classical GMRES for a given input matrix size; it is not the case for the multisplitting method. \RC{CE attention tu n'as pas mis de label dans tes figures, donc c'est le bordel, j'en mets mais vérifie...} @@@ -524,9 -524,9 +524,9 @@@ grid architectures, even with the sam and 4x8). We can observ the low sensitivity of the Krylov multisplitting method (compared with the classical GMRES) when scaling up the number of the processors in the grid: in average, the GMRES (resp. Multisplitting) algorithm performs -40\% better (resp. 48\%) less when running from 2x16=32 to 8x8=64 processors. +$40\%$ better (resp. $48\%$) when running from 2x16=32 to 8x8=64 processors. -\subsubsection{Running on two different speed cluster inter-networks} +\subsubsection{Running on two different inter-clusters network speed} \ \\ \begin{figure} [ht!] @@@ -536,7 -536,7 +536,7 @@@ Grid & 2x16, 4x8\\ %\hline Network & N1 : bw=10Gbs-lat=8.10$^{-6}$ \\ %\hline - & N2 : bw=1Gbs-lat=5.10$^{-5}$ \\ - Input matrix size & N$_{x}$ x N$_{y}$ x N$_{z}$ =150 x 150 x 150\\ \hline + Input matrix size & N$_{x}$ x N$_{y}$ x N$_{z}$ =150 x 150 x 150\\ \hline \end{tabular} \caption{Clusters x Nodes - Networks N1 x N2} \end{center} @@@ -557,10 -557,9 +557,10 @@@ These experiments compare the behavio speed inter-cluster network (N1) and also on a less performant network (N2). Figure~\ref{fig:02} shows that end users will gain to reduce the execution time for both algorithms in using a grid architecture like 4x16 or 8x8: the -performance was increased in a factor of 2. The results depict also that when +performance was increased by a factor of $2$. The results depict also that when the network speed drops down (12.5\%), the difference between the execution times can reach more than 25\%. \RC{c'est pas clair : la différence entre quoi et quoi?} +\DL{pas clair} \subsubsection{Network latency impacts on performance} \ \\ @@@ -572,7 -571,7 +572,7 @@@ Network & N1 : bw=1Gbs \\ %\hline Input matrix size & N$_{x}$ x N$_{y}$ x N$_{z}$ =150 x 150 x 150\\ \hline \end{tabular} -\caption{Network latency impact} +\caption{Network latency impacts} \end{figure} @@@ -580,20 -579,20 +580,20 @@@ \begin{figure} [ht!] \centering \includegraphics[width=100mm]{network_latency_impact_on_execution_time.pdf} -\caption{Network latency impact on execution time} +\caption{Network latency impacts on execution time} \label{fig:03} \end{figure} -According the results in Figure~\ref{fig:03}, a degradation of the network -latency from 8.10$^{-6}$ to 6.10$^{-5}$ implies an absolute time increase more -than 75\% (resp. 82\%) of the execution for the classical GMRES (resp. Krylov +According to the results of Figure~\ref{fig:03}, a degradation of the network +latency from $8.10^{-6}$ to $6.10^{-5}$ implies an absolute time increase of more +than $75\%$ (resp. $82\%$) of the execution for the classical GMRES (resp. Krylov multisplitting) algorithm. In addition, it appears that the Krylov multisplitting method tolerates more the network latency variation with a less rate increase of the execution time. Consequently, in the worst case -(lat=6.10$^{-5 }$), the execution time for GMRES is almost the double than the +($lat=6.10^{-5 }$), the execution time for GMRES is almost the double than the time of the Krylov multisplitting, even though, the performance was on the same -order of magnitude with a latency of 8.10$^{-6}$. +order of magnitude with a latency of $8.10^{-6}$. \subsubsection{Network bandwidth impacts on performance} \ \\ @@@ -605,17 -604,19 +605,17 @@@ Network & N1 : bw=1Gbs - lat=5.10$^{-5}$ \\ %\hline Input matrix size & N$_{x}$ x N$_{y}$ x N$_{z}$ =150 x 150 x 150\\ \hline \\ \end{tabular} -\caption{Network bandwidth impact} +\caption{Network bandwidth impacts} \end{figure} \begin{figure} [ht!] \centering \includegraphics[width=100mm]{network_bandwith_impact_on_execution_time.pdf} -\caption{Network bandwith impact on execution time} +\caption{Network bandwith impacts on execution time} \label{fig:04} \end{figure} - - The results of increasing the network bandwidth show the improvement of the performance for both algorithms by reducing the execution time (see Figure~\ref{fig:04}). However, in this case, the Krylov multisplitting method @@@ -629,7 -630,7 +629,7 @@@ of 40\% which is only around 24\% for c \begin{tabular}{r c } \hline Grid & 4x8\\ %\hline - Network & N2 : bw=1Gbs - lat=5.10$^{-5}$ \\ + Network & N2 : bw=1Gbs - lat=5.10$^{-5}$ \\ Input matrix size & N$_{x}$ = From 40 to 200\\ \hline \end{tabular} \caption{Input matrix size impact} @@@ -690,32 -691,30 +690,30 @@@ powerful CPU \subsection{Comparing GMRES in native synchronous mode and the multisplitting algorithm in asynchronous mode} The previous paragraphs put in evidence the interests to simulate the behavior - of the application before any deployment in a real environment. We have focused - the study on analyzing the performance in varying the key factors impacting the - results. The study compares the performance of the two proposed algorithms both - in \textit{synchronous mode }. In this section, following the same previous - methodology, the goal is to demonstrate the efficiency of the multisplitting - method in \textit{ asynchronous mode} compared with the classical GMRES staying - in \textit{synchronous mode}. - - Note that the interest of using the asynchronous mode for data exchange - is mainly, in opposite of the synchronous mode, the non-wait aspects of - the current computation after a communication operation like sending - some data between nodes. Each processor can continue their local - calculation without waiting for the end of the communication. Thus, the - asynchronous may theoretically reduce the overall execution time and can - improve the algorithm performance. - - As stated supra, Simgrid simulator tool has been used to prove the - efficiency of the multisplitting in asynchronous mode and to find the - best combination of the grid resources (CPU, Network, input matrix size, - \ldots ) to get the highest \textit{"relative gain"} (exec\_time$_{GMRES}$ / exec\_time$_{multisplitting}$) in comparison with the classical GMRES time. + of the application before any deployment in a real environment. In this + section, following the same previous methodology, our goal is to compare the + efficiency of the multisplitting method in \textit{ asynchronous mode} with the + classical GMRES in \textit{synchronous mode}. + + The interest of using an asynchronous algorithm is that there is no more + synchronization. With geographically distant clusters, this may be essential. + In this case, each processor can compute its iteration freely without any + synchronization with the other processors. Thus, the asynchronous may + theoretically reduce the overall execution time and can improve the algorithm + performance. + + \RC{la phrase suivante est bizarre, je ne comprends pas pourquoi elle vient ici} + As stated before, the Simgrid simulator tool has been successfully used to show + the efficiency of the multisplitting in asynchronous mode and to find the best + combination of the grid resources (CPU, Network, input matrix size, \ldots ) to + get the highest \textit{"relative gain"} (exec\_time$_{GMRES}$ / + exec\_time$_{multisplitting}$) in comparison with the classical GMRES time. The test conditions are summarized in the table below : \\ - % environment - \begin{footnotesize} + \begin{figure} [ht!] + \centering \begin{tabular}{r c } \hline Grid & 2x50 totaling 100 processors\\ %\hline @@@ -725,15 -724,17 +723,17 @@@ Input matrix size & N$_{x}$ = From 62 to 150\\ %\hline Residual error precision & 10$^{-5}$ to 10$^{-9}$\\ \hline \\ \end{tabular} - \end{footnotesize} + \end{figure} - Again, comprehensive and extensive tests have been conducted varying the - CPU power and the network parameters (bandwidth and latency) in the - simulator tool with different problem size. The relative gains greater - than 1 between the two algorithms have been captured after each step of - the test. Table 7 below has recorded the best grid configurations - allowing the multisplitting method execution time more performant 2.5 times than - the classical GMRES execution and convergence time. The experimentation has demonstrated the relative multisplitting algorithm tolerance when using a low speed network that we encounter usually with distant clusters thru the internet. + Again, comprehensive and extensive tests have been conducted with different + parametes as the CPU power, the network parameters (bandwidth and latency) in + the simulator tool and with different problem size. The relative gains greater + than 1 between the two algorithms have been captured after each step of the + test. In Figure~\ref{table:01} are reported the best grid configurations + allowing the multisplitting method to be more than 2.5 times faster than the + classical GMRES. These experiments also show the relative tolerance of the + multisplitting algorithm when using a low speed network as usually observed with + geographically distant clusters throuth the internet. % use the same column width for the following three tables \newlength{\mytablew}\settowidth{\mytablew}{\footnotesize\np{E-11}} @@@ -744,14 -745,12 +744,12 @@@ \end{tabular}} - \begin{table}[!t] - \centering + \begin{figure}[!t] + \centering + %\begin{table} % \caption{Relative gain of the multisplitting algorithm compared with the classical GMRES} % \label{"Table 7"} - Table 7. Relative gain of the multisplitting algorithm compared with - the classical GMRES \\ - - \begin{mytable}{11} + \begin{mytable}{11} \hline bandwidth (Mbit/s) & 5 & 5 & 5 & 5 & 5 & 50 & 50 & 50 & 50 & 50 \\ @@@ -772,7 -771,11 +770,11 @@@ & 2.52 & 2.55 & 2.52 & 2.57 & 2.54 & 2.53 & 2.51 & 2.58 & 2.55 & 2.54 \\ \hline \end{mytable} - \end{table} + %\end{table} + \caption{Relative gain of the multisplitting algorithm compared with the classical GMRES} + \label{table:01} + \end{figure} + \section{Conclusion} CONCLUSION