writeLB.tex

\begin{frame}[fragile]
\frametitle{How to write your own Load Balancer}
\begin{itemize}
\item Statistics collected by Charm
\begin{lstlisting}[basicstyle=\tiny]
struct LDStats { // load balancing database
  ProcStats  *procs; //statistics of PEs
  int count;

  int   n_objs;
  int   n_migrateobjs;
  LDObjData* objData; //info regarding chares

  int   n_comm;
  LDCommData* commData; //communication information

  int  *from_proc, *to_proc; //residence of
  chares
}
\end{lstlisting}
\item Use LDStats, ProcArray and ObjGraph for processor load and communication
statistics
\item \emph{work} is the function invoked by Charm RTS to perform load balancing
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{Example Strategy - BFS}
\begin{lstlisting}[basicstyle=\tiny]
void GraphBFTLB::work(LDStats *stats) {
  ProcArray *parr = new ProcArray(stats);       // Processor Array
  ObjGraph *ogr = new ObjGraph(stats);          // Object Graph

  double avgLoad = parr->getAverageLoad();
  parr->resetTotalLoad();

  int numPes = parr->procs.size(), start = 0, nextPe = 0, i, nbr;
  std::queue<int> vertexq;

  vertexq.push(start);
  ogr->vertices[start].setNewPe(nextPe);
  parr->procs[nextPe].totalLoad() += ogr->vertices[start].getVertexLoad();

  while(!vertexq.empty()) {
    start = vertexq.front(); vertexq.pop();
    for(i = 0; i < ogr->vertices[start].sendToList.size(); i++) {

      // look at all neighbors of a node in the queue and map them
      nbr = ogr->vertices[start].sendToList[i].getNeighborId();
      if(ogr->vertices[nbr].getNewPe() == -1) {
        vertexq.push(nbr);
        if(parr->procs[nextPe].getTotalLoad() + ogr->vertices[nbr].getVertexLoad() > avgLoad) { 
          nextPe++;
          avgLoad += (avgLoad - parr->procs[nextPe].getTotalLoad())/(numPes-nextPe);
        }
        ogr->vertices[nbr].setNewPe(nextPe);
        parr->procs[nextPe].totalLoad() += ogr->vertices[nbr].getVertexLoad();
      }
    }
  }   
  ogr->convertDecisions(stats); // Send decisions back to LDStats 
}
\end{lstlisting}
\end{frame}