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[Enhancement] Support gather operation in NCCL backend #1061

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[Enhancement] Support gather operation in NCCL backend #1061

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8ba956f
Support gather operation in NCCL backend
sh0622-kim Apr 9, 2023
5922097
add unit-test
sh0622-kim Apr 10, 2023
4464ee6
fix lint
sh0622-kim Apr 10, 2023
dc3277e
Add multi-node support to Gather with NCCL backend
sh0622-kim Apr 20, 2023
9781b98
change to all_gather
sh0622-kim Apr 23, 2023
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12 changes: 8 additions & 4 deletions mmengine/dist/dist.py
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Original file line number Diff line number Diff line change
Expand Up @@ -186,9 +186,6 @@ def gather(data: Tensor,
Calling ``gather`` in non-distributed environment dose nothing
and just returns a list containing :attr:`data` itself.

Note:
``NCCL`` backend does not support ``gather``.

Note:
Unlike PyTorch ``torch.distributed.gather``, :meth:`gather` in
MMEngine does not pass in an empty list ``gather_list`` and returns
Expand Down Expand Up @@ -251,7 +248,14 @@ def gather(data: Tensor,
else:
gather_list = []

torch_dist.gather(data, gather_list, dst, group)
# Check if the backend is NCCL
if get_backend(group) == torch_dist.Backend.NCCL:
if get_rank(group) == dst:
gather_list = torch.cuda.comm.gather(data, dst, group)
else:
torch.cuda.comm.gather(data, dst, group)
else:
torch_dist.gather(data, gather_list, dst, group)

if get_rank(group) == dst:
return cast_data_device(gather_list, input_device) # type: ignore
Expand Down