关于机器学习:MindSpore易点通如何将PyTorch源码转成MindSpore低阶API并在Ascend芯片上实现单机单卡训练

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1 概述本文将介绍如何将 PyTorch 源码转换成 MindSpore 低阶 API 代码, 并在 Ascend 芯片上实现单机单卡训练。下图展现了 MindSpore 高阶 API、低阶 API 和 PyTorch 的训练流程的区别。

与 MindSpore 高阶 API 雷同，低阶 API 训练也须要进行：配置运行信息、数据读取和预处理、网络定义、定义损失函数和优化器。具体步骤同高阶 API。2 结构模型 (低阶 API) 结构模型时，首先将网络原型与损失函数封装，再将组合的模型与优化器封装，最终组合成一个可用于训练的网络。因为训练并验证中，需计算在训练集上的精度，因而返回值中需蕴含网络的输入值。import mindspore from mindspore
import Modelimport mindspore.nn as nnfrom mindspore.ops
import functional as Ffrom mindspore.ops
import operations as P
class BuildTrainNetwork(nn.Cell):

'''Build train network.'''
def __init__(self, my_network, my_criterion, train_batch_size, class_num):
    super(BuildTrainNetwork, self).__init__()
    self.network = my_network
    self.criterion = my_criterion
    self.print = P.Print()

# Initialize self.output

    self.output = mindspore.Parameter(Tensor(np.ones((train_batch_size,
                    class_num)), mindspore.float32), requires_grad=False)

def construct(self, input_data, label):
    output = self.network(input_data)

# Get the network output and assign it to self.output

    self.output = output
    loss0 = self.criterion(output, label)
    return loss0

class TrainOneStepCellV2(TrainOneStepCell):

'''Build train network.'''
def __init__(self, network, optimizer, sens=1.0):
    super(TrainOneStepCellV2, self).__init__(network, optimizer, sens=1.0)

def construct(self, *inputs):
    weights = self.weights
    loss = self.network(*inputs)

# Obtain self.network from BuildTrainNetwork

    output = self.network.output
    sens = P.Fill()(P.DType()(loss), P.Shape()(loss), self.sens)

# Get the gradient of the network parameters

    grads = self.grad(self.network, weights)(*inputs, sens)
    grads = self.grad_reducer(grads)

# Optimize model parameters

    loss = F.depend(loss, self.optimizer(grads))
    return loss, output

# Construct model
model_constructed = BuildTrainNetwork(net, loss_function, TRAIN_BATCH_SIZE, CLASS_NUM)
model_constructed = TrainOneStepCellV2(model_constructed, opt)3 训练并验证（低阶 API）和 PyTorch 中相似，采纳低阶 API 进行网络训练并验证。具体步骤如下：class CorrectLabelNum(nn.Cell):

def __init__(self):
    super(CorrectLabelNum, self).__init__()
    self.print = P.Print()
    self.argmax = mindspore.ops.Argmax(axis=1)
    self.sum = mindspore.ops.ReduceSum()

def construct(self, output, target):
    output = self.argmax(output)
    correct = self.sum((output == target).astype(mindspore.dtype.float32))
    return correct

def train_net(model, network, criterion,

epoch_max, train_path, val_path,
train_batch_size, val_batch_size,
repeat_size):

"""define the training method"""

# Create dataset

ds_train, steps_per_epoch_train = create_dataset(train_path,
    do_train=True, batch_size=train_batch_size, repeat_num=repeat_size)
ds_val, steps_per_epoch_val = create_dataset(val_path, do_train=False,
            batch_size=val_batch_size, repeat_num=repeat_size)

# CheckPoint CallBack definition

config_ck = CheckpointConfig(save_checkpoint_steps=steps_per_epoch_train,
                            keep_checkpoint_max=epoch_max)
ckpoint_cb = ModelCheckpoint(prefix="train_resnet_cifar10",
                            directory="./", config=config_ck)

# Create dict to save internal callback object’s parameters

cb_params = _InternalCallbackParam()
cb_params.train_network = model
cb_params.epoch_num = epoch_max
cb_params.batch_num = steps_per_epoch_train
cb_params.cur_epoch_num = 0
cb_params.cur_step_num = 0
run_context = RunContext(cb_params)
ckpoint_cb.begin(run_context)

print("============== Starting Training ==============")
correct_num = CorrectLabelNum()
correct_num.set_train(False)

for epoch in range(epoch_max):
    print("Epoch:", epoch+1, "/", epoch_max)
    train_loss = 0
    train_correct = 0
    train_total = 0  
    for _, (data, gt_classes) in enumerate(ds_train):
        model.set_train()
        loss, output = model(data, gt_classes)
        train_loss += loss
        correct = correct_num(output, gt_classes)
        correct = correct.asnumpy()
        train_correct += correct.sum()

# Update current step number

        cb_params.cur_step_num += 1

# Check whether to save checkpoint or not

        ckpoint_cb.step_end(run_context)

    cb_params.cur_epoch_num += 1
    my_train_loss = train_loss/steps_per_epoch_train
    my_train_accuracy = 100*train_correct/(train_batch_size*
                            steps_per_epoch_train)
    print('Train Loss:', my_train_loss)
    print('Train Accuracy:', my_train_accuracy, '%')

    print('evaluating {}/{} ...'.format(epoch + 1, epoch_max))
    val_loss = 0
    val_correct = 0
    for _, (data, gt_classes) in enumerate(ds_val):
        network.set_train(False)
        output = network(data)
        loss = criterion(output, gt_classes)
        val_loss += loss
        correct = correct_num(output, gt_classes)
        correct = correct.asnumpy()
        val_correct += correct.sum()

    my_val_loss = val_loss/steps_per_epoch_val
    my_val_accuracy = 100*val_correct/(val_batch_size*steps_per_epoch_val)
    print('Validation Loss:', my_val_loss)
    print('Validation Accuracy:', my_val_accuracy, '%')

print("--------- trains out ---------")4 运行脚本启动命令：python MindSpore_1P_low_API.py --data_path=xxx --epoch_num=xxx 在开发环境的 Terminal 中运行脚本，能够看到网络输入后果：

注：因为高阶 API 采纳数据下沉模式进行训练，而低阶 API 不反对数据下沉训练，因而高阶 API 比低阶 API 训练速度快。性能比照：低阶 API: 2000 imgs/sec；高阶 API: 2200 imgs/sec 具体代码请返回 MindSpore 论坛进行下载：华为云论坛_云计算论坛_开发者论坛_技术论坛 - 华为云

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