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Made MPI calls in exchangeStateVectors non-blocking #380

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Sep 21, 2023
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Made MPI calls in exchangeStateVectors non-blocking #380

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28 changes: 19 additions & 9 deletions QuEST/src/CPU/QuEST_cpu_distributed.c
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Original file line number Diff line number Diff line change
Expand Up @@ -494,8 +494,12 @@ void densmatr_initPureState(Qureg targetQureg, Qureg copyQureg) {

void exchangeStateVectors(Qureg qureg, int pairRank){
// MPI send/receive vars
int TAG=100;
MPI_Status status;
int sendTag;
int recvTag;
int rank;
MPI_Request * requests;

MPI_Comm_rank(MPI_COMM_WORLD, &rank);

// Multiple messages are required as MPI uses int rather than long long int for count
// For openmpi, messages are further restricted to 2GB in size -- do this for all cases
Expand All @@ -506,20 +510,26 @@ void exchangeStateVectors(Qureg qureg, int pairRank){

// safely assume MPI_MAX... = 2^n, so division always exact
int numMessages = qureg.numAmpsPerChunk/maxMessageCount;
requests = (MPI_Request*) malloc(4 * numMessages * sizeof(MPI_Request));
int i;
long long int offset;

// send my state vector to pairRank's qureg.pairStateVec
// receive pairRank's state vector into qureg.pairStateVec
for (i=0; i<numMessages; i++){
offset = i*maxMessageCount;
MPI_Sendrecv(&qureg.stateVec.real[offset], maxMessageCount, MPI_QuEST_REAL, pairRank, TAG,
&qureg.pairStateVec.real[offset], maxMessageCount, MPI_QuEST_REAL,
pairRank, TAG, MPI_COMM_WORLD, &status);
//printf("rank: %d err: %d\n", qureg.rank, err);
MPI_Sendrecv(&qureg.stateVec.imag[offset], maxMessageCount, MPI_QuEST_REAL, pairRank, TAG,
&qureg.pairStateVec.imag[offset], maxMessageCount, MPI_QuEST_REAL,
pairRank, TAG, MPI_COMM_WORLD, &status);
sendTag = rank * numMessages + i;
recvTag = pairRank * numMessages + i;

MPI_Isend(&qureg.stateVec.real[offset], maxMessageCount, MPI_QuEST_REAL, pairRank, sendTag, MPI_COMM_WORLD, requests + 4*i);
MPI_Isend(&qureg.stateVec.imag[offset], maxMessageCount, MPI_QuEST_REAL, pairRank, sendTag, MPI_COMM_WORLD, requests + 4*i + 1);
MPI_Irecv(&qureg.pairStateVec.real[offset], maxMessageCount, MPI_QuEST_REAL, pairRank, recvTag, MPI_COMM_WORLD, requests + 4*i + 2);
MPI_Irecv(&qureg.pairStateVec.imag[offset], maxMessageCount, MPI_QuEST_REAL, pairRank, recvTag, MPI_COMM_WORLD, requests + 4*i + 3);
}

MPI_Waitall(4 * numMessages, requests, MPI_STATUSES_IGNORE);

free(requests);
}

void exchangePairStateVectorHalves(Qureg qureg, int pairRank){
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