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-%\documentclass[12pt,twocolumn]{article}
+\documentclass[conference]{IEEEtran}
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% \usepackage{secdot}
%\usepackage[font={footnotesize,bt}]{caption}
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-\usepackage{lmodern}
-\usepackage{todonotes}
-\newcommand{\AG}[2][inline]{\todo[color=green!50,#1]{\sffamily\small\textbf{AG:} #2}}
+\usepackage{xspace}
+\usepackage[textsize=footnotesize]{todonotes}
+\newcommand{\AG}[2][inline]{\todo[color=green!50,#1]{\sffamily\textbf{AG:} #2}\xspace}
\begin{document}
\title{Optimal Dynamic Frequency Scaling for Energy-Performance of Parallel MPI Programs}
-\author{A. Badri \and J.-C. Charr \and R. Couturier \and A. Giersch}
+
+\author{%
+ \IEEEauthorblockN{%
+ Ahmed Badri,
+ Jean-Claude Charr,
+ Raphaël Couturier and
+ Arnaud Giersch
+ }
+ \IEEEauthorblockA{%
+ FEMTO-ST Institute\\
+ University of Franche-Comté
+ }
+}
+
\maketitle
-\AG{``Optimal'' is a bit pretentious in the title}
+\AG{``Optimal'' is a bit pretentious in the title.\\
+ Complete affiliation, add an email address, etc.}
\begin{abstract}
- \AG{FIXME}
+ \AG{complete the abstract\dots}
\end{abstract}
\section{Introduction}
+\label{sec.intro}
The need for computing power is still increasing and it is not expected to slow
down in the coming years. To satisfy this demand, researchers and supercomputers
constructors have been regularly increasing the number of computing cores in
-supercomputers (for example in November 2013, according to the top 500
+supercomputers (for example in November 2013, according to the TOP500
list~\cite{43}, the Tianhe-2 was the fastest supercomputer. It has more than 3
millions of cores and delivers more than 33 Tflop/s while consuming 17808
kW). This large increase in number of computing cores has led to large energy
benchmarks (NPB v3.3) developed by NASA~\cite{44}. Our experiments are executed
using the simulator SimGrid/SMPI v3.10~\cite{Casanova:2008:SGF:1397760.1398183}
over an homogeneous distributed memory architecture. Furthermore, we compare the
-proposed algorithm with Rauber's methods. The comparison's results show that our
+proposed algorithm with Rauber's methods.
+\AG{Add citation for Rauber's methods. Moreover, Rauber was not alone to to this work (use ``Rauber et al.'', or ``Rauber and Gudula'', or \dots)}
+The comparison's results show that our
algorithm gives better energy-time trade off.
+%
+\AG{Correctly reword the following}%
+In Section~\ref{sec.relwork} we present works from other
+authors. Then, in Sections~\ref{sec.ptasks} and~\ref{sec.energy}, we
+introduce our model. [\dots] Finally, we conclude in
+Section~\ref{sec.concl}.
\section{Related Works}
+\label{sec.relwork}
+
+\AG{Consider introducing the models (sec.~\ref{sec.ptasks},
+ maybe~\ref{sec.energy}) before related works}
In the this section some heuristics, to compute the scaling factor, are
presented and classified in two parts : offline and online methods.
The DVFS offline methods are static and are not executed during the runtime of
the program. Some approaches used heuristics to select the best DVFS state
during the compilation phases as an example in Azevedo et al.~\cite{40}. He used
-intra-task algorithm to choose the DVFS setting when there are dependency points
+intra-task algorithm
+\AG{what is an ``intra-task algorithm''?}
+to choose the DVFS setting when there are dependency points
between tasks. While in~\cite{29}, Xie et al. used breadth-first search
algorithm to do that. Their goal is saving energy with time limits. Another
approaches gathers and stores the runtime information for each DVFS state, then
\end{enumerate}
\section{Parallel Tasks Execution on Homogeneous Platform}
+\label{sec.ptasks}
A homogeneous cluster consists of identical nodes in terms of the hardware and
the software. Each node has its own memory and at least one processor which can
executed on this model can be either synchronous or asynchronous. In this paper
we consider execution of the synchronous tasks on distributed homogeneous
platform. These tasks can exchange the data via synchronous memory passing.
-\begin{figure}[h]
+\begin{figure*}[t]
\centering
- \subfloat[Synch. Imbalanced Communications]{\includegraphics[scale=0.67]{synch_tasks}\label{fig:h1}}
- \subfloat[Synch. Imbalanced Computations]{\includegraphics[scale=0.67]{compt}\label{fig:h2}}
+ \subfloat[Sync. Imbalanced Communications]{\includegraphics[scale=0.67]{synch_tasks}\label{fig:h1}}
+ \subfloat[Sync. Imbalanced Computations]{\includegraphics[scale=0.67]{compt}\label{fig:h2}}
\caption{Parallel Tasks on Homogeneous Platform}
\label{fig:homo}
-\end{figure}
+\end{figure*}
+\AG{On fig.~\ref{fig:h1}, how can there be a synchronization point without communications just before ?\\
+Use ``Sync.'' to abbreviate ``Synchronization''}
Therefore, the execution time of a task consists of the computation time and the
communication time. Moreover, the synchronous communications between tasks can
lead to idle time while tasks wait at the synchronous point for others tasks to
where $T_i$ is the execution time of process $i$.
\section{Energy Model for Homogeneous Platform}
+\label{sec.energy}
The energy consumption by the processor consists of two powers metric: the
dynamic and the static power. This general power formulation is used by many
the supply voltage $V$ and operational frequency $f$ respectively as follow :
\begin{equation}
\label{eq:pd}
- P_{dyn} = \alpha \cdot C_L \cdot V^2 \cdot f
+ \textit P_{dyn} = \alpha \cdot C_L \cdot V^2 \cdot f
\end{equation}
The static power $P_{static}$ captures the leakage power consumption as well as
the power consumption of peripheral devices like the I/O subsystem.
\begin{equation}
\label{eq:ps}
- P_{static} = V \cdot N \cdot K_{design} \cdot I_{leak}
+ \textit P_{static} = V \cdot N \cdot K_{design} \cdot I_{leak}
\end{equation}
where V is the supply voltage, N is the number of transistors, $K_{design}$ is a
design dependent parameter and $I_{leak}$ is a technology-dependent
parameter. Energy consumed by an individual processor $E_{ind}$ is the summation
of the dynamic and the static power multiply by the execution time for example
-see~\cite{36,15} .
+see~\cite{36,15}.
\begin{equation}
\label{eq:eind}
- E_{ind} = ( P_{dyn} + P_{static} ) \cdot T
+ \textit E_{ind} = ( P_{dyn} + P_{static} ) \cdot T
\end{equation}
The dynamic voltage and frequency scaling (DVFS) is a process that allowed in
modern processors to reduce the dynamic power by scaling down the voltage and
frequency. Its main objective is to reduce the overall energy
consumption~\cite{37}. The operational frequency \emph f depends linearly on the
-supply voltage $V$, i.e., $V = \beta . f$ with some constant $\beta$. This
+supply voltage $V$, i.e., $V = \beta \cdot f$ with some constant $\beta$. This
equation is used to study the change of the dynamic voltage with respect to
various frequency values in~\cite{3}. The reduction process of the frequency are
expressed by scaling factor \emph S. The scale \emph S is the ratio between the
maximum and the new frequency as in EQ~(\ref{eq:s}).
\begin{equation}
\label{eq:s}
- S = \frac{F_{max}}{F_{new}}
+ S = \frac{F_{max}}{F_{new}}
\end{equation}
-The value of the scale \emph S is grater than 1 when changing the frequency to
-any new frequency value(\emph {P-state}) in governor. It is equal to 1 when the
+The value of the scale $S$ is greater than 1 when changing the frequency to
+any new frequency value (\emph {P-state}) in governor.
+\AG{Explain what's a governor}
+It is equal to 1 when the
frequency are set to the maximum frequency. The energy consumption model for
parallel homogeneous platform is depending on the scaling factor \emph S. This
factor reduces quadratically the dynamic power. Also, this factor increases the
scaling factor as in EQ~(\ref{eq:sopt}).
\begin{equation}
\label{eq:sopt}
- S_{opt} = \sqrt[3]{\frac{2}{n} \cdot \frac{P_{dyn}}{P_{static}} \cdot
+ \textit S_{opt} = \sqrt[3]{\frac{2}{n} \cdot \frac{P_{dyn}}{P_{static}} \cdot
\left( 1 + \sum_{i=2}^{N} \frac{T_i^3}{T_1^3} \right) }
\end{equation}
\section{Performance Evaluation of MPI Programs}
+\label{sec.mpip}
The performance (execution time) of the parallel MPI applications are depends on
the time of the slowest task as in figure~(\ref{fig:homo}). Normally the
EQ~(\ref{eq:tnew}).
\begin{equation}
\label{eq:tnew}
- T_{new} = T_{\textit{Max Comp Old}} \cdot S + T_{\textit{Max Comm Old}}
+ \textit T_{new} = T_{\textit{Max Comp Old}} \cdot S + T_{\textit{Max Comm Old}}
\end{equation}
The above equation shows that the scaling factor \emph S has linear relation
with the computation time without affecting the communication time. The
investigation study for the EQ~(\ref{eq:tnew}).
\section{Performance Prediction Verification}
+\label{sec.verif}
In this section we evaluate the precision of our performance prediction methods
on the NAS benchmark. We use the EQ~(\ref{eq:tnew}) that predicts the execution
time values. These scaling factors are computed by dividing the maximum
frequency by the new one see EQ~(\ref{eq:s}). In all tests, we use the simulator
SimGrid/SMPI v3.10 to run the NAS programs.
-\AG{Fig.~\ref{fig:pred} is hard to read when printed in black and white,
- especially the ``Normalize Real Perf.'' curve.}
-\begin{figure}[width=\textwidth,height=\textheight,keepaspectratio]
+\begin{figure*}[t]
\centering
- \includegraphics[scale=0.60]{cg_per.eps}
- \includegraphics[scale=0.60]{mg_pre.eps}
- \includegraphics[scale=0.60]{bt_pre.eps}
- \includegraphics[scale=0.60]{lu_pre.eps}
+ \includegraphics[width=.4\textwidth]{cg_per.eps}\qquad%
+ \includegraphics[width=.4\textwidth]{mg_pre.eps}
+ \includegraphics[width=.4\textwidth]{bt_pre.eps}\qquad%
+ \includegraphics[width=.4\textwidth]{lu_pre.eps}
\caption{Fitting Predicted to Real Execution Time}
\label{fig:pred}
-\end{figure}
+\end{figure*}
%see Figure~\ref{fig:pred}
In our cluster there are 18 available frequency states for each processor from
2.5 GHz to 800 MHz, there is 100 MHz difference between two successive
figure~(\ref{fig:pred}).
\section{Performance to Energy Competition}
+\label{sec.compet}
+
This section demonstrates our approach for choosing the optimal scaling
factor. This factor gives maximum energy reduction taking into account the
-execution time for both computation and communication times . The relation
+execution time for both computation and communication times. The relation
between the energy and the performance are nonlinear and complex, because the
relation of the energy with scaling factor is nonlinear and with the performance
it is linear see~\cite{17}. The relation between the energy and the performance
For solving this problem, we normalize the energy by calculating the ratio
between the consumed energy with scaled frequency and the consumed energy
without scaled frequency :
-\begin{equation}
+\begin{multline}
\label{eq:enorm}
- E_\textit{Norm} = \frac{E_{Reduced}}{E_{Original}}
- = \frac{ P_{dyn} \cdot S_i^{-2} \cdot
+ \textit E_{Norm} = \frac{\textit E_{Reduced}}{\textit E_{Original}} \\
+ {} = \frac{ P_{dyn} \cdot S_i^{-2} \cdot
\left( T_1 + \sum_{i=2}^{N}\frac{T_i^3}{T_1^2}\right) +
P_{static} \cdot T_1 \cdot S_i \cdot N }{
P_{dyn} \cdot \left(T_1+\sum_{i=2}^{N}\frac{T_i^3}{T_1^2}\right) +
P_{static} \cdot T_1 \cdot N }
-\end{equation}
+\end{multline}
\AG{Use \texttt{\textbackslash{}text\{xxx\}} or
\texttt{\textbackslash{}textit\{xxx\}} for all subscripted words in equations
(e.g. \mbox{\texttt{E\_\{\textbackslash{}text\{Norm\}\}}}).
By the same way we can normalize the performance as follows :
\begin{equation}
\label{eq:pnorm}
- P_{Norm} = \frac{T_{New}}{T_{Old}}
+\textit P_{Norm} = \frac{\textit T_{New}}{\textit T_{Old}}
= \frac{T_{\textit{Max Comp Old}} \cdot S +
- T_{\textit{Max Comm Old}}}{T_{Old}}
+ T_{\textit{Max Comm Old}}}{\textit T_{Old}}
\end{equation}
The second problem is the optimization operation for both energy and performance
is not in the same direction. In other words, the normalized energy and the
performance as follows :
\begin{equation}
\label{eq:pnorm_en}
- P^{-1}_{Norm} = \frac{T_{Old}}{T_{New}}
- = \frac{T_{Old}}{T_{\textit{Max Comp Old}} \cdot S +
+\textit P^{-1}_{Norm} = \frac{\textit T_{Old}}{\textit T_{New}}
+ = \frac{\textit T_{Old}}{T_{\textit{Max Comp Old}} \cdot S +
T_{\textit{Max Comm Old}}}
\end{equation}
-\begin{figure}
+\begin{figure*}
\centering
- \subfloat[Converted Relation.]{\includegraphics[scale=0.70]{file.eps}\label{fig:r1}}
- \subfloat[Real Relation.]{\includegraphics[scale=0.70]{file3.eps}\label{fig:r2}}
+ \subfloat[Converted Relation.]{%
+ \includegraphics[width=.33\textwidth]{file.eps}\label{fig:r1}}%
+ \qquad%
+ \subfloat[Real Relation.]{%
+ \includegraphics[width=.33\textwidth]{file3.eps}\label{fig:r2}}
\label{fig:rel}
\caption{The Energy and Performance Relation}
-\end{figure}
+\end{figure*}
Then, we can modelize our objective function as finding the maximum distance
between the energy curve EQ~(\ref{eq:enorm}) and the inverse of performance
curve EQ~(\ref{eq:pnorm_en}) over all available scaling factors. This represent
following form:
\begin{equation}
\label{eq:max}
- \textit{MaxDist} = \max (\overbrace{P^{-1}_{Norm}}^{\text{Maximize}} -
- \overbrace{E_{Norm}}^{\text{Minimize}} )
+ \textit{MaxDist} = \max (\overbrace{\textit P^{-1}_{Norm}}^{\text{Maximize}} -
+ \overbrace{\textit E_{Norm}}^{\text{Minimize}} )
\end{equation}
Then we can select the optimal scaling factor that satisfy the
EQ~(\ref{eq:max}). Our objective function can works with any energy model or
reasons that mentioned before.
\section{Optimal Scaling Factor for Performance and Energy}
+\label{sec.optim}
In the previous section we described the objective function that satisfy our
goal in discovering optimal scaling factor for both performance and energy at
the same time. Therefore, we develop an energy to performance scaling algorithm
(EPSA). This algorithm is simple and has a direct way to calculate the optimal
scaling factor for both energy and performance at the same time.
-\begin{algorithm}[t]
+\begin{algorithm}[tp]
\caption{EPSA}
\label{EPSA}
\begin{algorithmic}[1]
%\begin{minipage}{\textwidth}
%\AG{Use the same format as for Algorithm~\ref{EPSA}}
-\begin{algorithm}[d]
+\begin{algorithm}[tp]
\caption{DVFS}
\label{dvfs}
\begin{algorithmic}
\State -Computations Section.
\State -Communications Section.
\If {$(J==1)$}
- \State -Gather all times of computation and\par
- \State communication from each node.
+ \State -Gather all times of computation and communication from\par each node.
\State -Call EPSA with these times.
\State -Calculate the new frequency from optimal scale.
\State -Set the new frequency to the system.
\EndFor
\end{algorithmic}
\end{algorithm}
-\clearpage
+
After obtaining the optimal scale factor from the EPSA algorithm. The program
calculates the new frequency $F_i$ for each task proportionally to its time
value $T_i$. By substitution of the EQ~(\ref{eq:s}) in the EQ~(\ref{eq:si}), we
the frequency according to the nodes workloads.
\section{Experimental Results}
+\label{sec.expe}
The proposed EPSA algorithm was applied to seven MPI programs of the NAS
benchmarks (EP, CG, MG, FT, BT, LU and SP). We work on three classes (A, B and
table~(\ref{table:platform}). Each node in the cluster has 18 frequency values
from 2.5 GHz to 800 MHz with 100 MHz difference between each two successive
frequencies.
-\begin{table}[ht]
+\begin{table}[htb]
\caption{Platform File Parameters}
% title of Table
\centering
- \AG{Use e.g. $5\times 10^{-7}$ instead of 5E-7}
\begin{tabular}{ | l | l | l |l | l |l |l | p{2cm} |}
\hline
Max & Min & Backbone & Backbone&Link &Link& Sharing \\
Freq. & Freq. & Bandwidth & Latency & Bandwidth& Latency&Policy \\ \hline
- 2.5 &800 & 2.25 GBps &$5\times 10^{-7} s$& 1 GBps & $5\times 10^{-5}$ s&Full \\
+ 2.5 &800 & 2.25 GBps &$5\times 10^{-7} s$& 1 GBps & $5\times 10^{-5} s$ &Full \\
GHz& MHz& & & & &Duplex \\\hline
\end{tabular}
\label{table:platform}
factors results for each program on class C. These factors give the maximum
energy saving percent and the minimum performance degradation percent in the
same time over all available scales.
-\begin{figure}[width=\textwidth,height=\textheight,keepaspectratio]
+\begin{figure*}[t]
\centering
- \includegraphics[scale=0.47]{ep.eps}
- \includegraphics[scale=0.47]{cg.eps}
- \includegraphics[scale=0.47]{sp.eps}
- \includegraphics[scale=0.47]{lu.eps}
- \includegraphics[scale=0.47]{bt.eps}
- \includegraphics[scale=0.47]{ft.eps}
+ \includegraphics[width=.33\textwidth]{ep.eps}\hfill%
+ \includegraphics[width=.33\textwidth]{cg.eps}\hfill%
+ \includegraphics[width=.33\textwidth]{sp.eps}
+ \includegraphics[width=.33\textwidth]{lu.eps}\hfill%
+ \includegraphics[width=.33\textwidth]{bt.eps}\hfill%
+ \includegraphics[width=.33\textwidth]{ft.eps}
\caption{Optimal scaling factors for The NAS MPI Programs}
\label{fig:nas}
-\end{figure}
-\begin{table}[width=\textwidth,height=\textheight,keepaspectratio]
+\end{figure*}
+\begin{table}[htb]
\caption{Optimal Scaling Factors Results}
% title of Table
\centering
BT & 1.31 &29.60&21.28 &8.32\\ \hline
SP & 1.38 &33.48&21.36 &12.12\\ \hline
FT & 1.47 &34.72&19.00 &15.72\\ \hline
- \end{tabular}
+ \end{tabular}
\label{table:factors results}
% is used to refer this table in the text
\end{table}
EPSA to selects smaller scaling factor values (inducing smaller energy savings).
\section{Comparing Results}
+\label{sec.compare}
In this section, we compare our EPSA algorithm results with Rauber's
methods~\cite{3}. He had two scenarios, the first is to reduce energy to optimal
Class A},\ref{table:compare Class B},\ref{table:compare Class C}). These
tables show the results of our EPSA and Rauber's two scenarios for all the NAS
benchmarks programs for classes A,B and C.
-\begin{table}[ht]
+\begin{table*}[p]
\caption{Comparing Results for The NAS Class A}
% title of Table
\centering
\end{tabular}
\label{table:compare Class A}
% is used to refer this table in the text
-\end{table}
-\begin{table}[ht]
+\end{table*}
+\begin{table*}[p]
\caption{Comparing Results for The NAS Class B}
% title of Table
\centering
\end{tabular}
\label{table:compare Class B}
% is used to refer this table in the text
-\end{table}
+\end{table*}
-\begin{table}[ht]
+\begin{table*}[p]
\caption{Comparing Results for The NAS Class C}
% title of Table
\centering
\end{tabular}
\label{table:compare Class C}
% is used to refer this table in the text
-\end{table}
+\end{table*}
As shown in these tables our scaling factor is not optimal for energy saving
such as Rauber's scaling factor EQ~(\ref{eq:sopt}), but it is optimal for both
the energy and the performance simultaneously. Our EPSA optimal scaling factors
paper. While the negative trade offs refers to improving energy saving (or may
be the performance) while degrading the performance (or may be the energy) more
than the first.
-\begin{figure}[width=\textwidth,height=\textheight,keepaspectratio]
+\begin{figure}[t]
\centering
- \includegraphics[scale=0.60]{compare_class_A.pdf}
- \includegraphics[scale=0.60]{compare_class_B.pdf}
- \includegraphics[scale=0.60]{compare_class_c.pdf}
- % use scale 35 for all to be in the same line
+ \includegraphics[width=.33\textwidth]{compare_class_A.pdf}
+ \includegraphics[width=.33\textwidth]{compare_class_B.pdf}
+ \includegraphics[width=.33\textwidth]{compare_class_c.pdf}
\caption{Comparing Our EPSA with Rauber's Methods}
\label{fig:compare}
\end{figure}
-\AG{\texttt{bibtex} gives many errors, please correct them !! Its correct }
-\clearpage
-\bibliographystyle{plain}
-\bibliography{my_reference}
+\section{Conclusion}
+\label{sec.concl}
+
+\AG{the conclusion needs to be written\dots{} one day}
+
+\section*{Acknowledgment}
+
+\AG{Right?}
+Computations have been performed on the supercomputer facilities of the
+Mésocentre de calcul de Franche-Comté.
+
+% trigger a \newpage just before the given reference
+% number - used to balance the columns on the last page
+% adjust value as needed - may need to be readjusted if
+% the document is modified later
+%\IEEEtriggeratref{15}
+
+\bibliographystyle{IEEEtran}
+\bibliography{IEEEabrv,my_reference}
\end{document}
%%% Local Variables:
%%% mode: latex
%%% TeX-master: t
%%% fill-column: 80
-%%%ispell-local-dictionary: "american"
+%%% ispell-local-dictionary: "american"
%%% End:
% LocalWords: Badri Charr FIXME Tianhe DVFS HPC NAS NPB SMPI Rauber's Rauber
-% LocalWords: CMOS EQ EPSA
+% LocalWords: CMOS EQ EPSA Franche Comté Tflop
