Gabriele Cosmo
95 lines
5.2 KiB
C++
95 lines
5.2 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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/// @file G4MPIutils.hh
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/// @brief Utility functions for MPI G4 interface
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#ifndef G4MPIUTILS_HH
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#define G4MPIUTILS_HH
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#include <functional>
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#include <map>
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#include <numeric>
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#include <vector>
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// Namespace with some utility functions for G4 MPI integration.
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// Main utilities:
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// G4mpi::Merge(...) : Merge results via a semi-optimized communication
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// patterns between ranks. Note that this implementation
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// is not topology aware. This means that MPI_Reduce and
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// MPI_Gather are more performant. However if you cannot
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// implement an appropriate MPI reducer or you cannot efford
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// the memory overhead of Gather, this can be used instead of
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// p2p communications.
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namespace G4mpi
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{
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// Simple data type representing a rank
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typedef unsigned int rank_t;
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// A couple of sending/receiving ranks
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typedef std::pair<rank_t, rank_t> couple_t;
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// This map represent, for each cycle (key) a set of communications
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// pairs
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typedef std::map<int, std::vector<couple_t>> commMap_t;
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// This function takes as input a vector of rank_t objects representing
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// a communication node identified by an ID (rank:int).
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// It returns a map of cycle:int -> vector<pairs<rank_t> >
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// Representing a sequence of communciation cycles. At each communication cycle
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// one or more p2p communications are established: in the pair the first element
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// is the sender and the second element of the pair is the receiver
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// At the end of the cycles all communications have been done to rank 0
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// For example with 4 nodes: [0,1,2,3] we have:
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// Cycle 0: (3->2),(1->0)
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// Cycle 1: (2->0)
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// With 5 nodes:
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// Cycle 0: (4->3),(2->1)
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// Cycle 1: (3->1)
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// Cycle 2: (1->0)
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// The algorithm can be used to implement a communication across mpi ranks
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// optimizing the network trafic. Each rank (the nodes) can send/receive to another node.
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// Once they have sent out the payload they become empty and non-active anymore.
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commMap_t buildCommunicationMap(std::vector<rank_t>& input);
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// Performs merging to rank 0 using the provided sender, receiver and barrier functions.
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// CommSize is the size of the communicator and myrank is the rank of the caller
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// For example: assume a class UserMerger has two members Send(uint) and
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// Receive(uint) and we are using a MPI_Comm object as
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// communicator, then to use this function the ranks can:
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// using std::placeholers::_1;
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// std::function<void(unsigned int)> sender =
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// std::bind(&Merger::Send,&mergerInst,_1);
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// std::function<void(unsigned int)> receiver =
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// std::bind(&Merger::Receiver,&mergerInst,_1);
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// std::function<void(void)> barrier =
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// [&commInst](){MPI_Barrier(commInst);};
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// G4mpi::Merge(sender,receiver,barrier,commSize,myrank);
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void Merge(std::function<void(unsigned int)> senderF, std::function<void(unsigned int)> receiverF,
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std::function<void(void)> barrierF, unsigned int commSize, unsigned int myrank);
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// Type representing a merging functions
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typedef std::function<void(std::function<void(unsigned int)>, std::function<void(unsigned int)>,
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std::function<void(void)>, unsigned int, unsigned int)>
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mergerHandler_t;
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} // namespace G4mpi
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#endif // G4MPIUTILS_HH
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