MueLu_RepartitionHeuristicFactory_def.hpp

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#ifndef PACKAGES_MUELU_SRC_REBALANCING_MUELU_REPARTITIONHEURISTICFACTORY_DEF_HPP_
#define PACKAGES_MUELU_SRC_REBALANCING_MUELU_REPARTITIONHEURISTICFACTORY_DEF_HPP_
 
#include <algorithm>
#include <iostream>
#include <sstream>
 
#ifdef HAVE_MPI
#include <Teuchos_DefaultMpiComm.hpp>
#include <Teuchos_CommHelpers.hpp>
 
//#include <Xpetra_Map.hpp>
#include <Xpetra_Matrix.hpp>
 
#include "MueLu_Utilities.hpp"
 
#include "MueLu_RAPFactory.hpp"
#include "MueLu_BlockedRAPFactory.hpp"
#include "MueLu_SubBlockAFactory.hpp"
#include "MueLu_Level.hpp"
#include "MueLu_MasterList.hpp"
#include "MueLu_Monitor.hpp"
 
#include "MueLu_RepartitionHeuristicFactory.hpp"
 
namespace MueLu {
 
 template <class Scalar, class LocalOrdinal, class GlobalOrdinal, class Node>
 RCP<const ParameterList> RepartitionHeuristicFactory<Scalar, LocalOrdinal, GlobalOrdinal, Node>::GetValidParameterList() const {
    RCP<ParameterList> validParamList = rcp(new ParameterList());
 
#define SET_VALID_ENTRY(name) validParamList->setEntry(name, MasterList::getEntry(name))
    SET_VALID_ENTRY("repartition: start level");
    SET_VALID_ENTRY("repartition: min rows per proc");
    SET_VALID_ENTRY("repartition: target rows per proc");
    SET_VALID_ENTRY("repartition: max imbalance");
#undef  SET_VALID_ENTRY
 
    validParamList->set< RCP<const FactoryBase> >("A", Teuchos::null, "Factory of the matrix A");
 
    return validParamList;
  }
 
  template <class Scalar, class LocalOrdinal, class GlobalOrdinal, class Node>
  void RepartitionHeuristicFactory<Scalar, LocalOrdinal, GlobalOrdinal, Node>::DeclareInput(Level &currentLevel) const {
    Input(currentLevel, "A");
  }
 
  template <class Scalar, class LocalOrdinal, class GlobalOrdinal, class Node>
  void RepartitionHeuristicFactory<Scalar, LocalOrdinal, GlobalOrdinal, Node>::Build(Level& currentLevel) const {
    FactoryMonitor m(*this, "Build", currentLevel);
 
    const Teuchos::ParameterList & pL = GetParameterList();
    // Access parameters here to make sure that we set the parameter entry flag to "used" even in case of short-circuit evaluation.
    // TODO (JG): I don't really know if we want to do this.
    const int    startLevel           = pL.get<int>   ("repartition: start level");
    const LO     minRowsPerProcess    = pL.get<LO>    ("repartition: min rows per proc");
          LO     targetRowsPerProcess = pL.get<LO>    ("repartition: target rows per proc");
    const double nonzeroImbalance     = pL.get<double>("repartition: max imbalance");
 
    if (targetRowsPerProcess == 0)
      targetRowsPerProcess = minRowsPerProcess;
 
    RCP<const FactoryBase> Afact = GetFactory("A");
    if(!Afact.is_null() && Teuchos::rcp_dynamic_cast<const RAPFactory>(Afact) == Teuchos::null &&
       Teuchos::rcp_dynamic_cast<const BlockedRAPFactory>(Afact) == Teuchos::null &&
       Teuchos::rcp_dynamic_cast<const SubBlockAFactory>(Afact) == Teuchos::null) {
      GetOStream(Warnings) <<
        "MueLu::RepartitionHeuristicFactory::Build: The generation factory for A must " \
        "be a RAPFactory or a SubBlockAFactory providing the non-rebalanced matrix information! " \
        "It specifically must not be of type Rebalance(Blocked)AcFactory or similar. " \
        "Please check the input. Make also sure that \"number of partitions\" is provided to " \
        "the Interface class and the RepartitionFactory instance.  Instead, we have a "<<Afact->description() << std::endl;
    }
    // TODO: We only need a CrsGraph. This class does not have to be templated on Scalar types.
    RCP<Matrix> A = Get< RCP<Matrix> >(currentLevel, "A");
 
    // ======================================================================================================
    // Determine whether partitioning is needed
    // ======================================================================================================
    // NOTE: most tests include some global communication, which is why we currently only do tests until we make
    // a decision on whether to repartition. However, there is value in knowing how "close" we are to having to
    // rebalance an operator. So, it would probably be beneficial to do and report *all* tests.
 
    // Test1: skip repartitioning if current level is less than the specified minimum level for repartitioning
    if (currentLevel.GetLevelID() < startLevel) {
      GetOStream(Statistics1) << "Repartitioning?  NO:" <<
          "\n  current level = " << Teuchos::toString(currentLevel.GetLevelID()) <<
          ", first level where repartitioning can happen is " + Teuchos::toString(startLevel) << std::endl;
 
      // a negative number of processors means: no repartitioning
      Set(currentLevel, "number of partitions", -1);
 
      return;
    }
 
    RCP<const Map> rowMap = A->getRowMap();
 
    RCP<const Teuchos::Comm<int> > origComm = rowMap->getComm();
    RCP<const Teuchos::Comm<int> > comm     = origComm;
 
    // Test 2: check whether A is actually distributed, i.e. more than one processor owns part of A
    // TODO: this global communication can be avoided if we store the information with the matrix (it is known when matrix is created)
    // TODO: further improvements could be achieved when we use subcommunicator for the active set. Then we only need to check its size
    {
      int numActiveProcesses = 0;
      MueLu_sumAll(comm, Teuchos::as<int>((A->getNodeNumRows() > 0) ? 1 : 0), numActiveProcesses);
 
      if (numActiveProcesses == 1) {
        GetOStream(Statistics1) << "Repartitioning?  NO:" <<
            "\n  # processes with rows = " << Teuchos::toString(numActiveProcesses) << std::endl;
 
        Set(currentLevel, "number of partitions", 1);
        return;
      }
    }
 
    bool test3 = false, test4 = false;
    std::string msg3, msg4;
 
    // Test3: check whether number of rows on any processor satisfies the minimum number of rows requirement
    // NOTE: Test2 ensures that repartitionning is not done when there is only one processor (it may or may not satisfy Test3)
    if (minRowsPerProcess > 0) {
      LO numMyRows = Teuchos::as<LO>(A->getNodeNumRows()), minNumRows, LOMAX = Teuchos::OrdinalTraits<LO>::max();
      LO haveFewRows = (numMyRows < minRowsPerProcess ? 1 : 0), numWithFewRows = 0;
      MueLu_sumAll(comm, haveFewRows, numWithFewRows);
      MueLu_minAll(comm, (numMyRows > 0 ? numMyRows : LOMAX), minNumRows);
 
      // TODO: we could change it to repartition only if the number of processors with numRows < minNumRows is larger than some
      // percentage of the total number. This way, we won't repartition if 2 out of 1000 processors don't have enough elements.
      // I'm thinking maybe 20% threshold. To implement, simply add " && numWithFewRows < .2*numProcs" to the if statement.
      if (numWithFewRows > 0)
        test3 = true;
 
      msg3 = "\n  min # rows per proc = " + Teuchos::toString(minNumRows) + ", min allowable = " + Teuchos::toString(minRowsPerProcess);
    }
 
    // Test4: check whether the balance in the number of nonzeros per processor is greater than threshold
    if (!test3) {
      GO minNnz, maxNnz, numMyNnz = Teuchos::as<GO>(A->getNodeNumEntries());
      MueLu_maxAll(comm, numMyNnz,                           maxNnz);
      MueLu_minAll(comm, (numMyNnz > 0 ? numMyNnz : maxNnz), minNnz); // min nnz over all active processors
      double imbalance = Teuchos::as<double>(maxNnz)/minNnz;
 
      if (imbalance > nonzeroImbalance)
        test4 = true;
 
      msg4 = "\n  nonzero imbalance = " + Teuchos::toString(imbalance) + ", max allowable = " + Teuchos::toString(nonzeroImbalance);
    }
 
    if (!test3 && !test4) {
      GetOStream(Statistics1) << "Repartitioning?  NO:" << msg3 + msg4 << std::endl;
 
      // A negative number of partitions means: no repartitioning
      Set(currentLevel, "number of partitions", -1);
      return;
    }
 
    GetOStream(Statistics1) << "Repartitioning? YES:" << msg3 + msg4 << std::endl;
 
    // ======================================================================================================
    // Calculate number of partitions
    // ======================================================================================================
    // FIXME Quick way to figure out how many partitions there should be (same algorithm as ML)
    // FIXME Should take into account nnz? Perhaps only when user is using min #nnz per row threshold.
 
    // The number of partitions is calculated by the RepartitionFactory and stored in "number of partitions" variable on
    // the current level. If this variable is already set (e.g., by another instance of RepartitionFactory) then this number
    // is used. The "number of partitions" variable serves as basic communication between the RepartitionFactory (which
    // requests a certain number of partitions) and the *Interface classes which call the underlying partitioning algorithms
    // and produce the "Partition" array with the requested number of partitions.
    const auto globalNumRows = Teuchos::as<GO>(A->getGlobalNumRows());
    int numPartitions = 1;
    if (globalNumRows >= targetRowsPerProcess) {
      // Make sure that each CPU thread has approximately targetRowsPerProcess
 
      int thread_per_mpi_rank = 1;
#if defined(HAVE_MUELU_KOKKOSCORE) && defined(KOKKOS_ENABLE_OPENMP)
      using execution_space = typename Node::device_type::execution_space;
      if (std::is_same<execution_space, Kokkos::OpenMP>::value)
        thread_per_mpi_rank = execution_space::concurrency();
#endif
 
      numPartitions = std::max(Teuchos::as<int>(globalNumRows / (targetRowsPerProcess * thread_per_mpi_rank)), 1);
    }
    numPartitions = std::min(numPartitions, comm->getSize());
 
    Set(currentLevel, "number of partitions", numPartitions);
 
    GetOStream(Statistics1) << "Number of partitions to use = " << numPartitions << std::endl;
  } // Build
} // namespace MueLu
 
#endif //ifdef HAVE_MPI
#endif /* PACKAGES_MUELU_SRC_REBALANCING_MUELU_REPARTITIONHEURISTICFACTORY_DEF_HPP_ */