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paddlepaddle--paddle/python/paddle/distributed/communication/all_reduce.py
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2026-07-13 12:40:42 +08:00

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# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from __future__ import annotations
from typing import TYPE_CHECKING
import paddle
from paddle.distributed.communication import stream
from paddle.distributed.communication.reduce import ReduceOp
if TYPE_CHECKING:
from paddle import Tensor
from paddle.base.core import task
from paddle.distributed.communication.group import Group
from paddle.distributed.communication.reduce import _ReduceOp
def all_reduce(
tensor: Tensor,
op: _ReduceOp = ReduceOp.SUM,
group: Group | None = None,
sync_op: bool = True,
) -> task:
"""
Reduce a tensor over all ranks so that all get the result.
As shown below, one process is started with a GPU and the data of this process is represented
by its group rank. The reduce operator is sum. Through all_reduce operator,
each GPU will have the sum of the data from all GPUs.
.. image:: https://githubraw.cdn.bcebos.com/PaddlePaddle/docs/develop/docs/api/paddle/distributed/img/allreduce.png
:width: 800
:alt: all_reduce
:align: center
Args:
tensor (Tensor): The input Tensor. It also works as the output Tensor. Its data type
should be float16, float32, float64, int32, int64, int8, uint8 or bool.
op (ReduceOp.SUM|ReduceOp.MAX|ReduceOp.MIN|ReduceOp.PROD|ReduceOp.AVG, optional): The operation used. Default value is ReduceOp.SUM.
group (Group|None, optional): The group instance return by new_group or None for global default group.
sync_op (bool, optional): Whether this op is a sync op. Default value is True.
Returns:
Return a task object.
Examples:
.. code-block:: pycon
>>> # doctest: +REQUIRES(env: DISTRIBUTED)
>>> import paddle
>>> import paddle.distributed as dist
>>> dist.init_parallel_env()
>>> if dist.get_rank() == 0:
... data = paddle.to_tensor([[4, 5, 6], [4, 5, 6]])
>>> else:
... data = paddle.to_tensor([[1, 2, 3], [1, 2, 3]])
>>> dist.all_reduce(data)
>>> print(data)
>>> # [[5, 7, 9], [5, 7, 9]] (2 GPUs)
"""
# AVG is only supported when nccl >= 2.10
if op == ReduceOp.AVG and paddle.base.core.nccl_version() < 21000:
group = (
paddle.distributed.collective._get_global_group()
if group is None
else group
)
tensor.scale_(1.0 / group.nranks)
return stream.all_reduce(
tensor,
op=ReduceOp.SUM,
group=group,
sync_op=sync_op,
use_calc_stream=False,
)
return stream.all_reduce(
tensor, op=op, group=group, sync_op=sync_op, use_calc_stream=False
)