91 lines
3.5 KiB
C++
91 lines
3.5 KiB
C++
/*************************************************************************
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* Copyright (c) 2015-2022, NVIDIA CORPORATION. All rights reserved.
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*
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* See LICENSE.txt for license information
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************************************************************************/
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#include "devcomm.h"
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#include "collectives.h"
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#include "primitives.h"
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namespace {
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template<typename T, typename RedOp, typename Proto>
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__device__ __forceinline__ void runRing(ncclWorkElem *args) {
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const int tid = threadIdx.x;
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const int nthreads = args->nWarps*WARP_SIZE;
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const int bid = args->bid;
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const int nChannels = args->nChannels;
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ncclRing *ring = &ncclShmem.channel.ring;
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int const *ringRanks = ring->userRanks;
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const ssize_t chunkSize = int(Proto::calcBytePerStep()/sizeof(T) * args->stepsPerSlice*args->slicesPerChunk);
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// We should not need the final /2 but it makes performance much, much smoother. Might be a bug somewhere.
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const ssize_t minChunkSizeLL128 = int(nthreads*(Proto::calcBytePerGrain()/sizeof(T))/2);
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const int nranks = ncclShmem.comm.nRanks;
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const ssize_t loopSize = nChannels*chunkSize;
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const ssize_t size = args->count;
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Primitives<T, RedOp, FanSymmetric<1>, 0, Proto, 0>
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prims(tid, nthreads, &ring->prev, &ring->next, args->sendbuff, args->recvbuff, args->redOpArg,
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args->stepsPerSlice, args->slicesPerChunk);
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for (ssize_t gridOffset = 0; gridOffset < size; gridOffset += loopSize) {
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ssize_t realChunkSize;
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if (Proto::Id == NCCL_PROTO_SIMPLE) {
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realChunkSize = min(chunkSize, divUp(size-gridOffset, nChannels));
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realChunkSize = roundUp(realChunkSize, (nthreads-WARP_SIZE)*sizeof(uint64_t)/sizeof(T));
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}
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else if (Proto::Id == NCCL_PROTO_LL)
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realChunkSize = size-gridOffset < loopSize ? args->lastChunkSize : chunkSize;
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else if (Proto::Id == NCCL_PROTO_LL128)
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realChunkSize = min(divUp(size-gridOffset, nChannels*minChunkSizeLL128)*minChunkSizeLL128, chunkSize);
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realChunkSize = int(realChunkSize);
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ssize_t chunkOffset = gridOffset + bid*int(realChunkSize);
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/////////////// begin ReduceScatter steps ///////////////
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ssize_t offset;
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int nelem = min(realChunkSize, size-chunkOffset);
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int rankDest;
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// step 0: push data to next GPU
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rankDest = ringRanks[nranks-1];
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offset = chunkOffset + rankDest * size;
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prims.send(offset, nelem);
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// k-2 steps: reduce and copy to next GPU
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for (int j=2; j<nranks; ++j) {
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rankDest = ringRanks[nranks-j];
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offset = chunkOffset + rankDest * size;
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prims.recvReduceSend(offset, nelem);
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}
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// step k-1: reduce this buffer and data, which will produce the final result
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rankDest = ringRanks[0];
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offset = chunkOffset + rankDest * size;
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prims.recvReduceCopy(offset, chunkOffset, nelem, /*postOp=*/true);
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}
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}
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}
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template<typename T, typename RedOp>
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struct RunWorkElement<ncclFuncReduceScatter, T, RedOp, NCCL_ALGO_RING, NCCL_PROTO_SIMPLE> {
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__device__ __forceinline__ void run(ncclWorkElem *args) {
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using Proto = ProtoSimple<>;
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runRing<T, RedOp, Proto>(args);
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}
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};
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template<typename T, typename RedOp>
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struct RunWorkElement<ncclFuncReduceScatter, T, RedOp, NCCL_ALGO_RING, NCCL_PROTO_LL> {
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__device__ __forceinline__ void run(ncclWorkElem *args) {
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runRing<T, RedOp, ProtoLL>(args);
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}
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};
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template<typename T, typename RedOp>
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struct RunWorkElement<ncclFuncReduceScatter, T, RedOp, NCCL_ALGO_RING, NCCL_PROTO_LL128> {
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__device__ __forceinline__ void run(ncclWorkElem *args) {
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runRing<T, RedOp, ProtoLL128>(args);
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}
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};
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