Function exchangeGpuSubBuffers

quest/src/comm/comm_routines.cpp:417–442

void exchangeGpuSubBuffers(Qureg qureg, qindex numAmps, int pairRank) {

    auto [sendInd, recvInd] = getSubBufferSendRecvInds(qureg);

    // exchange GPU memory directly if possible
    if (gpu_isDirectGpuCommPossible()) {

        // ensure GPU is finished modifying gpuCommBuffer
        gpu_sync();

        // communicate via GPUDirect or Peer-to-Peer
        exchangeArrays(&qureg.gpuCommBuffer[sendInd], &qureg.gpuCommBuffer[recvInd], numAmps, pairRank);
    
    // otherwise route the memory through the CPU
    } else {

        // copy GPU memory (buffer) into CPU memory (amps), preserving offset
        gpu_copyGpuToCpu(qureg, &qureg.gpuCommBuffer[sendInd], &qureg.cpuAmps[sendInd], numAmps);

        // exchange CPU memory (amps) to other node's CPU memory (buffer), receiving at index 0
        exchangeArrays(&qureg.cpuAmps[sendInd], &qureg.cpuCommBuffer[recvInd], numAmps, pairRank);

        // copy CPU memory (buffer) to GPU memory (buffer), receiving at index 0
        gpu_copyCpuToGpu(qureg, &qureg.cpuCommBuffer[recvInd], &qureg.gpuCommBuffer[recvInd], numAmps);
    }
}


void asynchSendGpuSubBuffer(Qureg qureg, qindex numElems, int pairRank) {