Add broadcast operators (#17503)

* This PR adds broadcast for multi-process. And it could be used in dynamic graph to broadcast parameters.

paddle/fluid/operators/distributed_ops/broadcast_op.cc

+/* Copyright (c) 2019 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. */
+
+#include <algorithm>
+#include <ostream>
+#include <utility>
+#include <vector>
+#include "paddle/fluid/framework/op_registry.h"
+
+namespace paddle {
+namespace operators {
+
+class BroadcastOp : public framework::OperatorWithKernel {
+ public:
+  using framework::OperatorWithKernel::OperatorWithKernel;
+
+  void InferShape(framework::InferShapeContext* ctx) const override {
+    PADDLE_ENFORCE(ctx->HasInput("X"),
+                   "Input(X) of BroadcastOp should not be null.");
+    PADDLE_ENFORCE(ctx->HasOutput("Out"),
+                   "Output(Output) of ConvOp should not be null.");
+  }
+};
+
+class BroadcastOpMaker : public framework::OpProtoAndCheckerMaker {
+ public:
+  void Make() {
+    AddInput("X", "(Tensor), tensor to be broadcast.");
+    AddOutput("Out", "(Tensor) the result of broadcast.");
+    AddAttr<bool>(
+        "sync_mode",
+        "(bool) whether to synchronize the CUDA stream after nccl call.")
+        .SetDefault(false);
+    AddAttr<int>("root", "(int).").SetDefault(0).EqualGreaterThan(0);
+    AddComment(R"DOC(
+***Broadcast Operator***
+
+Call NCCL Broadcast internally. Note that this op must be used when one
+thread is managing one GPU device.
+)DOC");
+  }
+};
+
+template <typename T>
+class BroadcastOpKernel : public framework::OpKernel<T> {
+ public:
+  void Compute(const framework::ExecutionContext& ctx) const override {
+    PADDLE_THROW("Broadcast op can run on gpu place only for now.");
+  }
+};
+
+}  // namespace operators
+}  // namespace paddle
+
+namespace ops = paddle::operators;
+namespace plat = paddle::platform;
+
+REGISTER_OP_WITHOUT_GRADIENT(broadcast, ops::BroadcastOp,
+                             ops::BroadcastOpMaker);
+
+REGISTER_OP_CPU_KERNEL(broadcast, ops::BroadcastOpKernel<float>,
+                       ops::BroadcastOpKernel<double>,
+                       ops::BroadcastOpKernel<int>,
+                       ops::BroadcastOpKernel<int64_t>,
+                       ops::BroadcastOpKernel<plat::float16>);

paddle/fluid/operators/distributed_ops/broadcast_op.cu.cc

+/* Copyright (c) 2019 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. */
+
+#include <algorithm>
+#include <utility>
+#include <vector>
+
+#include "paddle/fluid/framework/data_type.h"
+#include "paddle/fluid/framework/lod_tensor.h"
+#include "paddle/fluid/framework/op_registry.h"
+
+#if defined(PADDLE_WITH_CUDA) && !defined(_WIN32)
+#include "paddle/fluid/platform/nccl_helper.h"
+#endif
+
+namespace ops = paddle::operators;
+namespace plat = paddle::platform;
+
+namespace paddle {
+namespace operators {
+
+template <typename T>
+class NCCLBroadcastOpKernel : public framework::OpKernel<T> {
+ public:
+  void Compute(const framework::ExecutionContext& ctx) const override {
+    PADDLE_ENFORCE(platform::is_gpu_place(ctx.GetPlace()),
+                   "The place of ExecutionContext should be CUDAPlace.");
+
+#if defined(PADDLE_WITH_CUDA) && !defined(_WIN32)
+    int dev_id = boost::get<platform::CUDAPlace>(ctx.GetPlace()).device;
+    int root_dev_id = ctx.Attr<int>("root");
+
+    auto in = ctx.Input<framework::Tensor>("X");
+    auto out = ctx.Output<framework::Tensor>("Out");
+    PADDLE_ENFORCE(out->IsInitialized(),
+                   "Currently, the output of broadcast op must be initialized, "
+                   "because this op can only be an In-Place operation.");
+    void* send_recv_buffer = out->mutable_data<T>(ctx.GetPlace());
+    PADDLE_ENFORCE_EQ(
+        send_recv_buffer, in->data<void>(),
+        "Currently, the broadcast op can only be an In-Place operation.");
+
+    auto& dev_ctx = ctx.template device_context<platform::CUDADeviceContext>();
+    auto comm = dev_ctx.nccl_comm();
+    auto stream = dev_ctx.stream();
+
+    PADDLE_ENFORCE(platform::dynload::ncclBcast(
+        send_recv_buffer, static_cast<size_t>(in->numel()),
+        platform::ToNCCLDataType(in->type()), root_dev_id, comm, stream));
+
+    VLOG(3) << "Bcast " << ctx.Inputs("X")[0] << ", (" << in->numel() << ")"
+            << " From " << root_dev_id << " to " << dev_id;
+
+    if (ctx.Attr<bool>("sync_mode")) {
+      PADDLE_ENFORCE(cudaStreamSynchronize(stream));
+    }
+#else
+    PADDLE_THROW("PaddlePaddle should compile with GPU.");
+#endif
+  }
+};
+
+}  // namespace operators
+}  // namespace paddle
+
+REGISTER_OP_CUDA_KERNEL(broadcast, ops::NCCLBroadcastOpKernel<float>,
+                        ops::NCCLBroadcastOpKernel<double>,
+                        ops::NCCLBroadcastOpKernel<int>,
+                        ops::NCCLBroadcastOpKernel<int64_t>,
+                        ops::NCCLBroadcastOpKernel<plat::float16>);

python/paddle/fluid/dygraph/layers.py

@@ -18,6 +18,7 @@ import sys
 import numpy as np
 import collections
 import six
+from . import parallel_helper
 from .. import unique_name
 from paddle.fluid import core
 from .layer_object_helper import LayerObjectHelper
@@ -154,6 +155,8 @@ class Layer(core.Layer):
     def __call__(self, *inputs):
         if not self._built:
             self.build_once(*inputs)
+            if parallel_helper._is_data_parallel_mode():
+                parallel_helper._broadcast_parameters(self._parameters.values())
 
         outputs = self.forward(*inputs)
         self._built = True

python/paddle/fluid/dygraph/parallel.py

@@ -17,8 +17,8 @@ import numpy as np
 
 from .. import core
 from . import layers
+from . import parallel_helper
 from .. import framework
-
 from ..layers import collective
 from . import to_variable
 
@@ -26,24 +26,29 @@ __all__ = ["prepare_context"]
 
 ParallelStrategy = core.ParallelStrategy
 
-__parallel_ctx__clz__ = None
-
 
-def prepare_context(parallel_strategy):
-    global __parallel_ctx__clz__
-    assert __parallel_ctx__clz__ is None, "ParallelContext can only be initialized once."
-    assert framework.in_dygraph_mode(
-    ) is True, "dygraph.parallel.prepare_context should be used with dygrahp mode."
+def prepare_context(strategy=None):
+    if strategy is None:
+        strategy = ParallelStrategy()
+        strategy.nranks = Env().nranks
+        strategy.local_rank = Env().local_rank
+        strategy.trainer_endpoints = Env().trainer_endpoints
+        strategy.current_endpoint = Env().current_endpoint
+    if strategy.nranks < 2:
+        return
+    assert framework.in_dygraph_mode() is True,\
+        "dygraph.parallel.prepare_context should be used with dygrahp mode."
     place = framework._current_expected_place()
-    assert place is not None, "dygraph.parallel.prepare_context should be used in fluid.dygraph.guard(place) guard."
-
+    assert place is not None, \
+        "dygraph.parallel.prepare_context should be used in fluid.dygraph.guard(place) guard."
     if isinstance(place, core.CUDAPlace):
-        __parallel_ctx__clz__ = core.NCCLParallelContext(parallel_strategy,
-                                                         place)
+        parallel_helper._set_parallel_ctx(
+            core.NCCLParallelContext(strategy, place))
     else:
         # TODO(Yancey1989): add Gloo Parallel Context to support CPU parallel computation
         assert ("Only support CUDAPlace for now.")
-    __parallel_ctx__clz__.init()
+    parallel_helper._init_parallel_ctx()
+    return strategy
 
 
 class Env(object):
@@ -77,9 +82,65 @@ class Env(object):
 
 
 class DataParallel(layers.Layer):
+    """
+    Runs the module with data parallelism.
+
+    Currently, DataParallel only supports to run the dynamic graph
+    with multi-process. The usage is:
+    `python -m paddle.distributed.launch --gpus 2 dynamic_graph_test.py`.
+    And the content of `dynamic_graph_test.py` is the code of examples.
+
+    Examples:
+        .. code-block:: python
+
+           import numpy as np
+           import paddle.fluid as fluid
+           import paddle.fluid.dygraph as dygraph
+           from paddle.fluid.optimizer import AdamOptimizer
+           from paddle.fluid.dygraph.nn import FC
+           from paddle.fluid.dygraph.base import to_variable
+
+           place = fluid.CUDAPlace(0)
+           with fluid.dygraph.guard(place=place):
+
+               # prepare the data parallel context
+               strategy=dygraph.parallel.prepare_context()
+
+               fc_layer = FC("FC", 10, act="softmax")
+               adam = fluid.optimizer.AdamOptimizer()
+
+               # make the module become the data parallelism module
+               fc_layer = dygraph.parallel.DataParallel(fc_layer, strategy)
+
+               x_data = np.random.random(size=[10, 1]).astype(np.float32)
+               data = to_variable(x_data)
+
+               hidden = fc_layer(data)
+               avg_loss = fluid.layers.mean(hidden)
+
+               # scale the loss according to the number of trainers.
+               avg_loss = fc_layer.scale_loss(avg_loss)
+
+               avg_loss.backward()
+
+               # collect the gradients of trainers.
+               fc_layer.apply_collective_grads()
+
+               adam.minimize(avg_loss)
+               fc_layer.clear_gradients()
+
+    Args:
+        layers(Layer): The module that should be executed by data parallel.
+        strategy(ParallelStrategy): The strategy of data parallelism.
+
+    Returns:
+        Layer: The data paralleled module.
+    """
+
     def __init__(self, layers, strategy):
         super(DataParallel,
               self).__init__(layers.full_name() + "_data_parallel")
+
         self._layers = layers
         self._strategy = strategy
 
@@ -87,8 +148,20 @@ class DataParallel(layers.Layer):
         return self._layers(*inputs, **kwargs)
 
     def scale_loss(self, loss):
-        if self._strategy.nranks < 2:
+        """
+        Scale the loss. In data parallel mode, the loss should be scale with
+        the number of trainers. If not in data parallel mode, return the loss
+        directly.
+
+        Args:
+            loss(Layer): The loss of the current Model.
+
+        Returns:
+            Layer: the scaled loss.
+        """
+        if not self._is_data_parallel_mode():
             return loss
+
         loss_scale = to_variable(
             np.array([self._strategy.nranks]).astype("float32"))
         loss_scale.stop_gradient = True
@@ -96,10 +169,14 @@ class DataParallel(layers.Layer):
         return loss
 
     def apply_collective_grads(self):
-        if self._strategy.nranks < 2:
+        """
+        AllReduce the Parameters' gradient.
+        """
+        if not self._is_data_parallel_mode():
             return
 
         for param in self._layers.parameters():
+            # NOTE(zcd): The grad_ivar maybe no generated.
             if param.trainable and param._ivar._grad_ivar():
                 g_var = framework.Variable(
                     block=self._helper.main_program.current_block(),
@@ -107,3 +184,6 @@ class DataParallel(layers.Layer):
                     stop_gradient=True,
                     ivar=param._ivar._grad_ivar())
                 collective._allreduce(g_var, g_var, sync_mode=True)
+
+    def _is_data_parallel_mode(self):
+        return self._strategy.nranks > 1

python/paddle/fluid/dygraph/parallel_helper.py

+# Copyright (c) 2019 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except jin 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.
+import os
+from ..layers import collective
+
+__parallel_ctx__clz__ = None
+
+
+def _is_data_parallel_mode():
+    global __parallel_ctx__clz__
+    return __parallel_ctx__clz__ is not None and int(
+        os.getenv("PADDLE_TRAINERS_NUM", "1")) > 1
+
+
+def _set_parallel_ctx(nccl_parallel_context):
+    global __parallel_ctx__clz__
+    assert __parallel_ctx__clz__ is None, \
+        "ParallelContext can only be initialized once."
+    __parallel_ctx__clz__ = nccl_parallel_context
+
+
+def _init_parallel_ctx():
+    global __parallel_ctx__clz__
+    assert __parallel_ctx__clz__ is not None, \
+        "ParallelContext should be initialized."
+    __parallel_ctx__clz__.init()
+
+
+def _broadcast_parameters(parameters):
+    for param in parameters:
+        if param.trainable:
+            collective._broadcast(param, 0, sync_mode=True)

python/paddle/fluid/layers/collective.py

@@ -46,3 +46,14 @@ def _allreduce(x, out=None, reduce_type="sum", sync_mode=False):
         attrs={"reduce_type": red_typ_int,
                "sync_mode": sync_mode})
     return out
+
+
+def _broadcast(x, root, sync_mode=False):
+    helper = LayerHelper("broadcast", **locals())
+    helper.append_op(
+        type='broadcast',
+        inputs={'X': [x]},
+        outputs={'Out': [x]},
+        attrs={"sync_mode": sync_mode,
+               "root": root})
+    return x