!680 modify gradient_accumulation and add example code

Merge pull request !680 from jinyaohui/master

tutorials/source_zh_cn/advanced_use/gradient_accumulation.md

@@ -28,7 +28,7 @@
   
 最终目的是为了达到跟直接用N*Mini-batch数据训练几乎同样的效果。
 
-> 本教程用于GPU、Ascend 910 AI处理器。
+> 本教程用于GPU、Ascend 910 AI处理器, 你可以在这里下载完整的样例代码：<https://gitee.com/mindspore/docs/tree/master/tutorials/tutorial_code/gradient_accumulation>
 
 ## 创建梯度累积模型
 
@@ -232,7 +232,7 @@ class TrainClear(Cell):
 ```
 
 ### 定义训练过程
-- 每个Mini-batch通过正反向训练计算loss和梯度，通过mini_steps控制每次更新参数前的累加次数。达到累加次数后进行参数更新和
+每个Mini-batch通过正反向训练计算loss和梯度，通过mini_steps控制每次更新参数前的累加次数。达到累加次数后进行参数更新和
 累加梯度变量清零。
 
 ```python
@@ -305,7 +305,7 @@ class GradientAccumulation:
 ```python
 if __name__ == "__main__":
     parser = argparse.ArgumentParser(description='MindSpore Gard Cumulative Example')
-    parser.add_argument('--device_target', type=str, default="Ascend", choices=['Ascend', 'GPU', 'CPU'],
+    parser.add_argument('--device_target', type=str, default="Ascend", choices=['Ascend', 'GPU'],
                         help='device where the code will be implemented (default: Ascend)')
     parser.add_argument('--data_path', type=str, default="./Data",
                         help='path where the dataset is saved')
@@ -346,7 +346,7 @@ if __name__ == "__main__":
     
 2. 查看保存的CheckPoint文件。
 
-    训练过程中保存了CheckPoint文件gradient_accumulation.ckpt，即模型文件。
+    训练过程中保存了CheckPoint文件`gradient_accumulation.ckpt`，即模型文件。
 
 **验证模型**
 

tutorials/tutorial_code/gradient_accumulation/train.py

+import argparse
+import os
+from collections.abc import Iterable
+
+import mindspore.nn as nn
+from mindspore import ParameterTuple
+from mindspore import context
+from mindspore.nn import Cell
+from mindspore.ops import composite as C
+from mindspore.ops import functional as F
+from mindspore.ops import operations as P
+from mindspore.train.dataset_helper import DatasetHelper
+from mindspore.train.serialization import _exec_save_checkpoint
+from model_zoo.official.cv.lenet.src.dataset import create_dataset
+from model_zoo.official.cv.lenet.src.lenet import LeNet5
+
+_sum_op = C.MultitypeFuncGraph("grad_sum_op")
+_clear_op = C.MultitypeFuncGraph("clear_op")
+
+
+@_sum_op.register("Tensor", "Tensor")
+def _cumulative_gard(grad_sum, grad):
+    """Apply gard sum to cumulative gradient."""
+    add = P.AssignAdd()
+    return add(grad_sum, grad)
+
+
+@_clear_op.register("Tensor", "Tensor")
+def _clear_grad_sum(grad_sum, zero):
+    """Apply zero to clear grad_sum."""
+    success = True
+    success = F.depend(success, F.assign(grad_sum, zero))
+    return success
+
+
+class TrainForwardBackward(Cell):
+    def __init__(self, network, optimizer, grad_sum, sens=1.0):
+        super(TrainForwardBackward, self).__init__(auto_prefix=False)
+        self.network = network
+        self.network.add_flags(defer_inline=True)
+        self.weights = ParameterTuple(network.trainable_params())
+        self.optimizer = optimizer
+        self.grad_sum = grad_sum
+        self.grad = C.GradOperation('grad', get_by_list=True, sens_param=True)
+        self.sens = sens
+        self.hyper_map = C.HyperMap()
+
+    def construct(self, *inputs):
+        weights = self.weights
+        loss = self.network(*inputs)
+        sens = P.Fill()(P.DType()(loss), P.Shape()(loss), self.sens)
+        grads = self.grad(self.network, weights)(*inputs, sens)
+        return F.depend(loss, self.hyper_map(F.partial(_sum_op), self.grad_sum, grads))
+
+
+class TrainOptim(Cell):
+    def __init__(self, optimizer, grad_sum):
+        super(TrainOptim, self).__init__(auto_prefix=False)
+        self.optimizer = optimizer
+        self.grad_sum = grad_sum
+
+    def construct(self):
+        return self.optimizer(self.grad_sum)
+
+
+class TrainClear(Cell):
+    def __init__(self, grad_sum, zeros):
+        super(TrainClear, self).__init__(auto_prefix=False)
+        self.grad_sum = grad_sum
+        self.zeros = zeros
+        self.hyper_map = C.HyperMap()
+
+    def construct(self):
+        seccess = self.hyper_map(F.partial(_clear_op), self.grad_sum, self.zeros)
+        return seccess
+
+
+class GradientAccumulation:
+    def __init__(self, network, loss_fn, optimizer):
+        self._network = network
+        self._loss_fn = loss_fn
+        self._optimizer = optimizer
+
+        params = self._optimizer.parameters
+        self._grad_sum = params.clone(prefix="grad_sum", init='zeros')
+        self._zeros = params.clone(prefix="zeros", init='zeros')
+        self._train_forward_backward = self._build_train_forward_backward_network()
+        self._train_optim = self._build_train_optim()
+        self._train_clear = self._build_train_clear()
+
+    @staticmethod
+    def _transform_callbacks(callbacks):
+        """Transform callback to a list."""
+        if callbacks is None:
+            return []
+
+        if isinstance(callbacks, Iterable):
+            return list(callbacks)
+
+        return [callbacks]
+
+    def _build_train_forward_backward_network(self):
+        """Build forward and backward network"""
+        network = self._network
+        network = nn.WithLossCell(network, self._loss_fn)
+        loss_scale = 1.0
+        network = TrainForwardBackward(network, self._optimizer, self._grad_sum, loss_scale).set_train()
+        return network
+
+    def _build_train_optim(self):
+        """Build optimizer network"""
+        network = TrainOptim(self._optimizer, self._grad_sum).set_train()
+        return network
+
+    def _build_train_clear(self):
+        """Build clear network"""
+        network = TrainClear(self._grad_sum, self._zeros).set_train()
+        return network
+
+    def train_process(self, epoch, train_dataset, mini_steps=None):
+        """
+        Training process. The data would be passed to network directly.
+        """
+        dataset_helper = DatasetHelper(train_dataset, dataset_sink_mode=False, epoch_num=epoch)
+
+        for i in range(epoch):
+            step = 0
+            for k, next_element in enumerate(dataset_helper):
+                loss = self._train_forward_backward(*next_element)
+                if (k + 1) % mini_steps == 0:
+                    step += 1
+                    print("epoch:", i + 1, "step:", step, "loss is ", loss)
+                    self._train_optim()
+                    self._train_clear()
+
+            train_dataset.reset()
+
+        _exec_save_checkpoint(self._train_forward_backward, "gradient_accumulation.ckpt", )
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(description='MindSpore Gard Cumulative Example')
+    parser.add_argument('--device_target', type=str, default="Ascend", choices=['Ascend', 'GPU'],
+                        help='device where the code will be implemented (default: Ascend)')
+    parser.add_argument('--data_path', type=str, default="./Data",
+                        help='path where the dataset is saved')
+    args = parser.parse_args()
+
+    context.set_context(mode=context.GRAPH_MODE, device_target=args.device_target)
+    ds_train = create_dataset(os.path.join(args.data_path, "train"), 32)
+
+    network = LeNet5(10)
+    net_loss = nn.SoftmaxCrossEntropyWithLogits(is_grad=False, sparse=True, reduction="mean")
+    net_opt = nn.Momentum(network.trainable_params(), 0.01, 0.9)
+    model = GradientAccumulation(network, net_loss, net_opt)
+
+    print("============== Starting Training ==============")
+    model.train_process(10, ds_train, mini_steps=4)