Why I train tutorial model on GPU taking more time than on CPU?

1 
import torch
import torch.nn as nn
import torch.optim as optim
import torchvision
import torchvision.transforms as transforms
import time

transform = transforms.Compose([transforms.ToTensor(),
                                transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))])

traindata = torchvision.datasets.CIFAR10("./data", train=True, transform=transform, download=True)
trainloader = torch.utils.data.DataLoader(traindata, batch_size=4, shuffle=True)

testdata = torchvision.datasets.CIFAR10("./data", train=False, transform=transform, download=True)
testloader = torch.utils.data.DataLoader(testdata, batch_size=4, shuffle=False)

class Net(nn.Module):

    def __init__(self):
        super(Net, self).__init__()
        self.conv = nn.Sequential(
            nn.Conv2d(3,6,5),
            nn.MaxPool2d(2,2),
            nn.Conv2d(6,16,5),
            nn.MaxPool2d(2, 2),
        )
        self.linear = nn.Sequential(
            nn.Linear(16 * 5 * 5, 160),
            nn.ReLU(),
            nn.Linear(160, 64),
            nn.ReLU(),
            nn.Linear(64, 10),
        )

    def forward(self, inputs):
        conv_output = self.conv(inputs)
        output = self.linear(conv_output.view(-1,16 * 5 * 5))
        return output

device = torch.device("cuda:0")
start = time.time()
model = Net()
model.to(device)
loss_fc = nn.CrossEntropyLoss()
optimizer = optim.SGD(model.parameters(), lr=0.001, momentum=0.9)

for epoch in range(10):
    for i,data in enumerate(trainloader,1):
        input, target = data
        input, target = input.to(device),target.to(device)

        pred = model(input)

        loss = loss_fc(pred, target)

        optimizer.zero_grad()
        loss.backward()
        optimizer.step()

        if i%2000 == 0:
            print("[{}, {}] loss:{:.4f}".format(epoch+1, i, loss.item()))

print("time taken:{:.3f}".format(time.time()-start))

The console print:

time taken:361.207

But if I train the model on CPU, the console print:

time taken:205.772

I checked the Task Manager when training on GPU,and the GPU Occupancy rate was only 5%-10%。
My GPU is GTX 1060 6GB

Why did it take more time on GPU than on CPU?