【MindSpore易点通】如何保存模型进行checkpoint对比以及Print算子使用说明

1 保存模型checkpoint对比

将其他框架的源码迁移至MindSpore后若出现精度问题，可以对比验证精度最大epoch的模型输出。

MindSpore代码和Pytorch代码，存在MindSpore验证集精度比Pytorch低的问题，下面描述如何对比验证精度最大epoch的模型输出来定位问题。

1.1准备工作

训练时，将Pytorch和MindSpore每个epoch的模型保存下来。

• Pytorch中设置如下,完整代码参见示例代码：

model.eval()if not os.path.isdir('checkpoint'):
os.mkdir('checkpoint')
torch.save(model.state_dict(), './checkpoint/'+ str(epoch) +
           "_" + str(my_val_accuracy) + '_resnet50.pth')

• MindSpore中设置如下，完整代码请见附件：

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)

其中save_checkpoint_steps为一个轮次中要执行的step数。keep_checkpoint_max为最大存储模型数目。

1.2打印模型输出

分别打印MindSpore和Pytorch中验证精度最大的epoch对应的模型。

• MindSpore模型加载并打印:

from mindspore import load_checkpoint
param_dict = load_checkpoint("./train_mindspore/train_resnet_cifar10_1-162_391.ckpt")for key in param_dict.keys():
    print(key,param_dict[key].data.asnumpy())

打印结果如下 :

conv1.weight [[[[-0.06971329 -0.00755827 -0.02128288]
   [-0.11358283  0.0838231   0.05153372]
   [-0.16815324  0.21193054  0.2659021 ]]
   ...

• Pytorch模型加载并打印：

import torch
model = torch.load('./checkpoint/174_0_resnet50.pth')
print(model)

打印结果如下 :

OrderedDict([('conv1.weight', tensor([[[[ 0.0798,  0.2771, -0.0230],
          [-0.4563, -0.4013,  0.2395],
          [-0.0804,  0.2683,  0.2198]],
          ...

1.3对比模型输出结果

对比模型的各项输出结果，若发现有某项输出不一致，则需要分析对应的算子，可在MindSpore API中搜索相应算子，并分析。

2 Print算子使用说明

MindSpore的自研Print算子可以将用户输入的Tensor或字符串信息打印出来。Print算子使用方法与其他算子相同，在网络中的__init__声明算子并在construct进行调用。

2.1打印正向输出

Print算子正向打印，简单示例如下 ：

class ResNet(nn.Cell):
    def __init__(self, num_blocks, num_classes=10):
        super(ResNet, self).__init__()
        self.conv1 = _conv2d(3, 64, kernel_size=3, stride=1, padding=1)
        self.bn1 = nn.BatchNorm2d(64)
        self.relu = nn.ReLU()
        self.print = P.Print()

def construct(self, x_input):
        x_input = self.conv1(x_input)
        self.print('output_conv1:', x_input)
        out = self.relu(x_input)
        return out

打印结果如下:

output_conv1:
Tensor(shape=[1, 64, 32, 32], dtype=Float32, value=
[[[[ 2.72979736e-02  5.00488281e-02  9.80834961e-02 ...  1.38671875e-01  1.46850586e-01  5.52673340e-02]
   [ 1.49291992e-01  1.49658203e-01  1.94824219e-01 ...  3.98193359e-01  3.90380859e-01  1.97875977e-01]
   [ 7.49511719e-02  7.70263672e-02  1.22924805e-01 ...  2.86865234e-01  2.58056641e-01  1.22192383e-01]
   ...

2.2打印模型权重

Print算子打印模型权重，简单示例如下:

class ResNet(nn.Cell):
    def __init__(self, num_blocks, num_classes=10):
        super(ResNet, self).__init__()
        self.conv1 = _conv2d(3, 64, kernel_size=3, stride=1, padding=1)
        self.bn1 = nn.BatchNorm2d(64)
        self.relu = nn.ReLU()
        self.print = P.Print()

def construct(self, x_input):
        x_input = self.conv1(x_input)
        self.print("self.conv1.weight:", self.conv1.weight)
        out = self.bn1(x_input)
        out = self.relu(out)
        return out

打印结果如下:

self.conv1.weight:
Tensor(shape=[64, 3, 3, 3], dtype=Float32, value=
[[[[ 1.87883265e-02  8.28264281e-02  3.95536423e-02]
   [ 1.72755457e-02 -2.93852817e-02  5.61546721e-02]
   [-2.40226928e-02  1.50793493e-01  1.78463876e-01]]
   ...

2.3打印反向梯度

Print算子反向打印，简单示例如下:

class ResNet(nn.Cell):
    def __init__(self, num_blocks, num_classes=10):
        super(ResNet, self).__init__()
        self.in_planes = 64
        self.conv1 = _conv2d(3, 64, kernel_size=3, stride=1, padding=1)
        self.bn1 = nn.BatchNorm2d(64)
        self.relu = nn.ReLU()
        self.print = P.Print()
        self.print_grad = P.InsertGradientOf(self.save_gradient)


def save_gradient(self, dout):
        return dout

    def construct(self, x_input):    
        x_input = self.conv1(x_input)
        out_grad = self.print_grad(x_input)
        self.print("out_grad_conv1",out_grad)
        out = self.bn1(x_input)
        out = self.relu(out)
        return out

打印结果如下:

out_grad_conv1
Tensor(shape=[128, 64, 32, 32], dtype=Float32, value=
[[[[-3.97216797e-01  4.74853516e-02  2.53417969e-01 ...  5.80749512e-02  7.40356445e-02  2.26806641e-01]
   [-1.38867188e+00 -1.12890625e+00 -7.66601562e-01 ... -7.64160156e-01 -8.21777344e-01 -2.39013672e-01]
   [-1.13964844e+00 -9.60449219e-01 -6.69921875e-01 ... -9.59472656e-01 -1.27050781e+00 -8.31054688e-01]
   ...

2.4具体示例

下面以一份有问题的MindSpore代码为例，描述如何通过print算子打印输出来定位问题。

问题现象：MindSpore验证集精度比Pytorch低

验证集精度：MindSpore:91.96%； Pytorch:92.58%。

准备工作

为保证Pytorch和MindSpore网络输入图片相同，代码做如下修改，Pytorch中代码也做对应修改。

（1）训练数据集shuffle设置为False:
复制

（2）数据转换中注释如下内容：

transform_data = C.Compose([
    # CV.RandomCrop((32, 32), (4, 4, 4, 4)),
    # CV.RandomHorizontalFlip(),
    CV.Rescale(rescale, shift),
    CV.Normalize((0.4914, 0.4822, 0.4465), (0.2023, 0.1994, 0.2010)),
    CV.HWC2CHW()])

措施：通过print逐层打印前向输出，对比输出数据数量级

打印网络每层输出，需要在init中加入self.print = P.Print()。主网络中打印方式如下：

class ResNet(nn.Cell):
    def __init__(self, num_blocks, num_classes=10):
        super(ResNet, self).__init__()
        self.in_planes = 64
        self.conv1 = nn.Conv2d(3, 64, kernel_size=3, stride=1, padding=1, pad_mode='pad', weight_init='Uniform')
        self.bn1 = nn.BatchNorm2d(64)
        self.relu = nn.ReLU()
        self.layer1 = self._make_layer(64, num_blocks[0], stride=1)
        self.layer2 = self._make_layer(128, num_blocks[1], stride=2)
        self.layer3 = self._make_layer(256, num_blocks[2], stride=2)
        self.layer4 = self._make_layer(512, num_blocks[3], stride=2)
        self.avgpool2d = nn.AvgPool2d(kernel_size=4, stride=4)
        self.reshape = mindspore.ops.Reshape()
        self.linear = nn.Dense(2048, num_classes)
        self.print = P.Print()

    def _make_layer(self, planes, num_blocks, stride):
        strides = [stride] + [1]*(num_blocks-1)
        layers = []
        for stride in strides:
            layers.append(ResidualBlock(self.in_planes, planes, stride))
            self.in_planes = EXPANSION*planes            
        return nn.SequentialCell(*layers)

    def construct(self, x_input):    
        x_input = self.conv1(x_input)
        self.print('output_conv1:', x_input)
        out = self.bn1(x_input)
        out = self.relu(out)
        self.print('output_relu:', out)
        out = self.layer1(out)
        self.print('output_layer1:', out)
        out = self.layer2(out)
        self.print('output_layer2:', out)
        out = self.layer3(out)
        self.print('output_layer3:', out)
        out = self.layer4(out)
        self.print('output_layer4:', out)
        out = self.avgpool2d(out)
        self.print('output_avgpool2d:', out)
        out = self.reshape(out, (out.shape[0], 2048))
        out = self.linear(out)
        self.print('output_linear:', out)
        return out

对比第一张图片的输出，发现output_conv1（卷积）输出的数据数量级不一致。

问题1：卷积权重初始化不一致

对比MindSpore和Pytorch中卷积入参，发现卷积权重初始化不一致。

MindSpore中，权重初始化用的是：normal方法。
 

class mindspore.nn.Conv2d(in_channels, out_channels, kernel_size, stride=1, pad_mode="same", padding=0, dilation=1, group=1, has_bias=False, weight_init="normal", bias_init="zeros", data_format="NCHW")

而Pytorch中，默认的权重初始化方法如下图所示：

解决方案：更新MindSpore中卷积权重初始化方法，与Pytorch中一致

将卷积算法改成如下形式：

def _conv2d(in_channel, out_channel, kernel_size, stride=1, padding=0):
    scale = math.sqrt(1/(in_channel*kernel_size*kernel_size))
    if padding == 0:
        return nn.Conv2d(in_channel, out_channel, kernel_size=kernel_size,
        stride=stride, padding=padding, pad_mode='same',
        weight_init=mindspore.common.initializer.Uniform(scale=scale))
    else:
        return nn.Conv2d(in_channel, out_channel, kernel_size=kernel_size,
        stride=stride, padding=padding, pad_mode='pad',
        weight_init=mindspore.common.initializer.Uniform(scale=scale))

问题2：全连接层中权重和偏差初始化方法不一致

根据问题1中的问题，检查其他算子是否有类似问题。发现MindSpore中nn.Dense和Pytorch中nn.linear的权重和偏差初始化方法有所差别。

解决方案：更新MindSpore全连接层中权重和偏差初始化方法，与Pytorch中一致

将MindSpore中nn.Dense算法做如下修改：

def _dense(in_channel, out_channel):
    scale = math.sqrt(1/in_channel)
    return nn.Dense(in_channel, out_channel,
    weight_init=mindspore.common.initializer.Uniform(scale=scale),
    bias_init=mindspore.common.initializer.Uniform(scale=scale))

更新后代码，继续从头开始训练，并逐层打印前向输出。

改进效果

所有算子前向输出数量级一致；

MindSpore验证集精度有所提升，较Pytorch高。

验证集精度：MindSpore:92.98%；Pytorch:92.58%。