X-Git-Url: https://bilbo.iut-bm.univ-fcomte.fr/and/gitweb/loba-papers.git/blobdiff_plain/1c24f60b352adf4db2002f7a82ca418cfc8d8add..99c4629e78a3a929c5ba423fc7d6f11cb495e6f1:/supercomp11/supercomp11.tex

diff --git a/supercomp11/supercomp11.tex b/supercomp11/supercomp11.tex
index a26ad3a..2f2dd31 100644
--- a/supercomp11/supercomp11.tex
+++ b/supercomp11/supercomp11.tex
@@ -195,11 +195,16 @@ condition or with a weaker condition.
 \section{Best effort strategy}
 \label{Best-effort}
 
-In this section we  describe  a new load-balancing strategy that we call
-\emph{best effort}.  The general idea behind this strategy is that each
-processor, that detects it has more load than some of its neighbors, 
-sends some load to the most of its less loaded neighbors, doing its
-best to reach the equilibrium between those neighbors and himself.
+In this section we describe a new load-balancing strategy that we call
+\emph{best effort}.  First, we explain the general idea behind this strategy,
+and then we describe some variants of this basic strategy.
+
+\subsection{Basic strategy}
+
+The general idea behind the \emph{best effort} strategy is that each processor,
+that detects it has more load than some of its neighbors, sends some load to the
+most of its less loaded neighbors, doing its best to reach the equilibrium
+between those neighbors and himself.
 
 More precisely, when a processor $i$ is in its load-balancing phase,
 he proceeds as following.
@@ -246,12 +251,28 @@ he proceeds as following.
   \end{equation*}
 \end{enumerate}
 
-\FIXME{describe parameter $k$}
+\subsection{Leveling the amount to send}
+
+With the aforementioned basic strategy, each node does its best to reach the
+equilibrium with its neighbors.  Since each node may be taking the same kind of
+decision at the same moment, there is the risk that a node receives load from
+several of its neighbors, and then is temporary going off the equilibrium state.
+This is particularly true with strongly connected applications.
+
+In order to reduce this effect, we add the ability to level the amount to send.
+The idea, here, is to make smaller steps toward the equilibrium, such as a
+potentially wrong decision has a lower impact.
+
+Concretely, once $s_{ij}$ has been evaluated as before, it is simply divided by
+some configurable factor.  That's what we named the ``parameter $k$'' in
+Section~\ref{Results}.  The amount of data to send is then $s_{ij}(t) = (\bar{x}
+- x^i_j(t))/k$.
+\FIXME{check the name ($k$)}
 
 \section{Other strategies}
 \label{Other}
 
-\FIXME{Réécrire en angliche.}
+\FIXME{Réécrire en anglais.}
 
 % \FIXME{faut-il décrire les stratégies makhoul et simple ?}
 
@@ -497,8 +518,9 @@ an amount of load at less than 1\% of the load average, during an arbitrary
 number of computing iterations (2000 in our case).
 
 Note that this convergence detection was implemented in a centralized manner.
-This is easy to do within the simulator, but it's obviously not realistic.  In
-a real application we would have chosen a decentralized convergence detection algorithm, like the one described in \cite{10.1109/TPDS.2005.2}.
+This is easy to do within the simulator, but it's obviously not realistic.  In a
+real application we would have chosen a decentralized convergence detection
+algorithm, like the one described in \cite{10.1109/TPDS.2005.2}.
 
 \paragraph{Platforms}
 
@@ -507,16 +529,21 @@ settings, we simulated the executions on two sorts of platforms.  These two
 sorts of platforms differ by their underlaid network topology.  On the one hand,
 we have homogeneous platforms, modeled as a cluster.  On the other hand, we have
 heterogeneous platforms, modeled as the interconnection of a number of clusters.
+
+The clusters were modeled by a fixed number of computing nodes interconnected
+through a backbone link.  Each computing node has a computing power of
+1~GFlop/s, and is connected to the backbone by a network link whose bandwidth is
+of 125~MB/s, with a latency of 50~$\mu$s.  The backbone has a network bandwidth
+of 2.25~GB/s, with a latency of 500~$\mu$s.
+
 The heterogeneous platform descriptions were created by taking a subset of the
 Grid'5000 infrastructure\footnote{Grid'5000 is a French large scale experimental
   Grid (see \url{https://www.grid5000.fr/}).}, as described in the platform file
 \texttt{g5k.xml} distributed with SimGrid.  Note that the heterogeneity of the
-platform only comes from the network topology.  The processor speeds, and
-network bandwidths were normalized since our algorithms currently are not aware
-of such heterogeneity.  We arbitrarily chose to fix the processor speed to
-1~GFlop/s, and the network bandwidth to 125~MB/s, with a latency of 50~$\mu$s,
-except for the links between geographically distant sites, where the network
-bandwidth was fixed to 2.25~GB/s, with a latency of 500~$\mu$s.
+platform here only comes from the network topology.  Indeed, since our
+algorithms currently do not handle heterogeneous computing resources, the
+processor speeds were normalized, and we arbitrarily chose to fix them to
+1~GFlop/s.
 
 Then we derived each sort of platform with four different number of computing
 nodes: 16, 64, 256, and 1024 nodes.
@@ -657,4 +684,4 @@ Taille : 10 100 très gros
 
 % LocalWords:  Raphaël Couturier Arnaud Giersch Abderrahmane Sider Franche ij
 % LocalWords:  Bertsekas Tsitsiklis SimGrid DASUD Comté Béjaïa asynchronism ji
-% LocalWords:  ik isend irecv Cortés et al chan ctrl fifo Makhoul
+% LocalWords:  ik isend irecv Cortés et al chan ctrl fifo Makhoul GFlop xml