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Exchange recvbuff at the beginning of the CUDA kernel call. #464

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Exchange recvbuff at the beginning of the CUDA kernel call. #464

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5b7b6e8
First version of recvbuff exchange.
Feb 19, 2025
67f1e00
fixed memchans assignment.
Feb 19, 2025
c5f3b60
Tested the exchange of recvbuff with scratch buff
Feb 19, 2025
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22 changes: 20 additions & 2 deletions apps/nccl/src/broadcast.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -20,16 +20,34 @@ __global__ void __launch_bounds__(1024, 1)
const size_t nThread = blockDim.x * gridDim.x;
const size_t nPeer = nRanksPerNode - 1;
const size_t chanOffset = nPeer * blockIdx.x;
const size_t peerRootIdx = (root == rank) ? nPeer : ((root < rank) ? root : (root - 1));

__shared__ mscclpp::DeviceHandle<mscclpp::MemoryChannel> memChans[NRANKS_PER_NODE - 1];
// if (threadIdx.x < nPeer) {
// memChans[threadIdx.x] = memoryChannels[chanOffset + threadIdx.x];
// memChans[threadIdx.x].relaxedSignal();
// memChans[threadIdx.x].wait();
// }

if (threadIdx.x < nPeer) {
// My Id in peer.
const size_t myIdInPeer = (threadIdx.x < rank) ? (rank - 1) : rank;
const size_t offset = myIdInPeer * sizeof(void *);
memChans[threadIdx.x] = memoryChannels[chanOffset + threadIdx.x];
memChans[threadIdx.x].relaxedSignal();
// Write recvbuff (64 bytes).
void **dst = reinterpret_cast<void **>(memChans[threadIdx.x].dst_); // Peer's scratchbuff.
*(dst + offset) = recvbuff;
memChans[threadIdx.x].signal();
//memChans[threadIdx.x].relaxedSignal();
memChans[threadIdx.x].wait();
}
__syncthreads();

const size_t peerRootIdx = (root == rank) ? nPeer : ((root < rank) ? root : (root - 1));
if (threadIdx.x < nPeer) {
void **scratch_ = reinterpret_cast<void **>(scratchbuff); // My scratchbuff.
printf("rank = %ld, recvbuff = %p, recvbuff_[0] = %p, recvbuff_[1] = %p\n", rank, recvbuff,
*scratch_, *(scratch_ + sizeof(void *)));
}

const size_t bytesPerGPU = nelemsPerGPU * sizeof(int);
const size_t bytes = bytesPerGPU;
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