rocm-systems/src/device/all_gather.h

/*************************************************************************
 * Copyright (c) 2015-2022, NVIDIA CORPORATION. All rights reserved.
 *
 * See LICENSE.txt for license information
 ************************************************************************/

#include "device.h"
#include "collectives.h"
#include "primitives.h"

namespace {
  template<typename T, typename RedOp, typename Proto>
  __device__ __forceinline__ void runRing(ncclWorkElem *args) {
    const int tid = threadIdx.x;
    const int nthreads = args->nWarps*WARP_SIZE;
    const int bid = args->bid;
    const int nChannels = args->nChannels;
    ncclRing *ring = &ncclShmem.channel.ring;
    const int *ringRanks = ring->userRanks;
    const ssize_t chunkSize = int(Proto::calcBytePerStep()/sizeof(T) * (Proto::Id == NCCL_PROTO_SIMPLE ? ALLGATHER_CHUNKSTEPS : 1));
    // We should not need the final /2 but it makes performance much, much smoother. Might be a bug somewhere.
    const ssize_t minChunkSizeLL128 = int(nthreads*(Proto::calcBytePerGrain()/sizeof(T))/2);
    const int nranks = ncclShmem.comm.nRanks;
    const ssize_t loopSize = nChannels*int(chunkSize);
    const ssize_t size = args->count;

    T *inputBuf = (T*)args->sendbuff;
    T *outputBuf = (T*)args->recvbuff;
    Primitives<T, RedOp, FanSymmetric<1>, 1, Proto, 0> prims
      (tid, nthreads, &ring->prev, &ring->next, inputBuf, outputBuf, args->redOpArg);

    for (ssize_t gridOffset = 0; gridOffset < size; gridOffset += loopSize) {
      ssize_t realChunkSize;
      if (Proto::Id == NCCL_PROTO_SIMPLE) {
        realChunkSize = min(chunkSize, divUp(size-gridOffset,nChannels));
        realChunkSize = roundUp(realChunkSize, (nthreads-WARP_SIZE)*sizeof(uint64_t)/sizeof(T));
      }
      else if (Proto::Id == NCCL_PROTO_LL)
        realChunkSize = size-gridOffset < loopSize ? args->lastChunkSize : chunkSize;
      else if (Proto::Id == NCCL_PROTO_LL128)
        realChunkSize = min(chunkSize, divUp(size-gridOffset, nChannels*minChunkSizeLL128)*minChunkSizeLL128);
      realChunkSize = int(realChunkSize);

      ssize_t chunkOffset = gridOffset + int(bid*realChunkSize);

      /////////////// begin AllGather steps ///////////////
      ssize_t offset;
      int nelem = min(realChunkSize, size-chunkOffset);
      int rankDest;

      // step 0: push data to next GPU
      rankDest = ringRanks[0];
      offset = chunkOffset + rankDest * size;

      if (inputBuf + chunkOffset == outputBuf + offset) { // In place
        prims.directSend(chunkOffset, offset, nelem);
      } else {
        prims.directCopySend(chunkOffset, offset, nelem);
      }

      // k-2 steps: copy to next GPU
      for (int j=1; j<nranks-1; ++j) {
        rankDest = ringRanks[nranks-j];
        offset = chunkOffset + rankDest * size;

        prims.directRecvCopySend(offset, nelem);
      }

      // Make final copy from buffer to dest.
      rankDest = ringRanks[1];
      offset = chunkOffset + rankDest * size;

      // Final wait/copy.
      prims.directRecv(offset, nelem);
    }
  }
}

template<typename T, typename RedOp>
struct RunWorkElement<ncclFuncAllGather, T, RedOp, NCCL_ALGO_RING, NCCL_PROTO_SIMPLE> {
  __device__ __forceinline__ void run(ncclWorkElem *args) {
    using Proto = ProtoSimple<ALLGATHER_CHUNKSTEPS/ALLGATHER_SLICESTEPS, ALLGATHER_SLICESTEPS>;
    runRing<T, RedOp, Proto>(args);
  }
};

template<typename T, typename RedOp>
struct RunWorkElement<ncclFuncAllGather, T, RedOp, NCCL_ALGO_RING, NCCL_PROTO_LL> {
  __device__ __forceinline__ void run(ncclWorkElem *args) {
    runRing<T, RedOp, ProtoLL>(args);
  }
};

template<typename T, typename RedOp>
struct RunWorkElement<ncclFuncAllGather, T, RedOp, NCCL_ALGO_RING, NCCL_PROTO_LL128> {
  __device__ __forceinline__ void run(ncclWorkElem *args) {
    runRing<T, RedOp, ProtoLL128>(args);
  }
};

template<typename T, typename RedOp>
struct RunWorkElement<ncclFuncAllGather, T, RedOp, NCCL_ALGO_NVLS, NCCL_PROTO_SIMPLE> {
  __device__ __forceinline__ void run(ncclWorkElem *args) {
    const int tid = threadIdx.x;
    const int bid = args->bid;
    const int nChannels = args->nChannels;
    struct ncclNvls* nvls = &ncclShmem.channel.nvls;
    const ssize_t chunkSize = int(args->lastChunkSize);
    const ssize_t size = args->count;
    const ssize_t loopSize = nChannels*chunkSize;
    const ssize_t rank = ncclShmem.comm.rank;

    const int nThreadsBcast = args->regUsed ? (NCCL_MAX_NTHREADS - WARP_SIZE) : 4 * WARP_SIZE;
    const int nThreadsGather = args->regUsed ? WARP_SIZE : NCCL_MAX_NTHREADS - nThreadsBcast;
    const int tidEndGather = nThreadsGather;
    const int tidEndBcast = tidEndGather + nThreadsBcast;

    if (!args->regUsed) {
      if (tid < tidEndGather) {
        // Gather
        using Proto = ProtoSimple<1, 1, COLL_UNROLL>;
        Primitives<T, RedOp, FanAsymmetric<NCCL_MAX_NVLS_ARITY, 0>, /*Direct=*/0, Proto, 0>
          prims(tid, nThreadsGather, nvls->up, NULL, NULL, args->recvbuff,
            args->redOpArg, 0 * Proto::MaxGroupWidth, 1, 1);
        for (ssize_t gridOffset = 0; gridOffset < size; gridOffset += loopSize) {
          ssize_t offset = gridOffset + bid * chunkSize;
          int nelem = min(chunkSize, size - offset);
          prims.gather(offset, nvls->nHeads * size, nelem, size, -1, 0);
        }
      } else if (tid < tidEndBcast) {
        // Bcast through NVLS
        using Proto = ProtoSimple<1, 1, COLL_UNROLL, 0, 1>;
        Primitives<T, RedOp, FanAsymmetric<0, 1>, /*Direct=*/0, Proto, 0>
          prims(tid - tidEndGather, nThreadsBcast, NULL, &nvls->down, args->sendbuff, NULL,
            args->redOpArg, 3 * Proto::MaxGroupWidth, 0, 0);
        for (ssize_t gridOffset = 0; gridOffset < size; gridOffset += loopSize) {
          ssize_t offset = gridOffset + bid * chunkSize;
          int nelem = min(chunkSize, size - offset);
          prims.send(offset, nelem);
        }
      }
    } else {
      /* direct allgather */
      if (tid < tidEndGather) {
        using Proto = ProtoSimple<1, 1, COLL_UNROLL>;
        Primitives<T, RedOp, FanSymmetric<NCCL_MAX_NVLS_ARITY>, /*Direct=*/0, Proto, 0>
          prims(tid, nThreadsGather, nvls->up, nvls->up, NULL, NULL,
            args->redOpArg, 0 * Proto::MaxGroupWidth, 1, 1);

        /* used as sync */
        prims.scatter(0, 0, 0, 0, -1, 0);

        for (ssize_t gridOffset = 0; gridOffset < size; gridOffset += loopSize) {
          prims.gather(0, 0, 0, 0, -1, 0);
        }
      } else if (tid < tidEndBcast) {
        using Proto = ProtoSimple<1, 1, COLL_UNROLL, 0, 1>;
        Primitives<T, RedOp, FanSymmetric<1>, /*Direct=*/1, Proto, 0>
          prims(tid - tidEndGather, nThreadsBcast, &nvls->down, &nvls->down, args->sendbuff, NULL,
            args->redOpArg, 1 * Proto::MaxGroupWidth, 0, 0, args);
        /* used as sync */
        prims.recv(0, 0);

        for (ssize_t gridOffset = 0; gridOffset < size; gridOffset += loopSize) {
          ssize_t inpOffset = gridOffset + bid * chunkSize;
          ssize_t outOffset = inpOffset + rank * size;
          int nelem = min(chunkSize, size - inpOffset);
          prims.directSend(inpOffset, outOffset, nelem);
        }
      }
    }
  }
};