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optional_data_parallelism.md
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可选择：数据并行处理（文末有完整代码下载）
作者：Sung Kim 和 Jenny Kang
在这个教程中，我们将学习如何用 DataParallel 来使用多 GPU。
通过 PyTorch 使用多个 GPU 非常简单。你可以将模型放在一个 GPU：
```python
device = torch.device("cuda:0")
model.to(device)
```
然后，你可以复制所有的张量到 GPU：
```python
mytensor = my_tensor.to(device)
```
请注意，只是调用 my_tensor.to(device) 返回一个 my_tensor 新的复制在GPU上，而不是重写 my_tensor。你需要分配给他一个新的张量并且在 GPU 上使用这个张量。
在多 GPU 中执行前馈，后馈操作是非常自然的。尽管如此，PyTorch 默认只会使用一个 GPU。通过使用 DataParallel 让你的模型并行运行，你可以很容易的在多 GPU 上运行你的操作。
```python
model = nn.DataParallel(model)
```
这是整个教程的核心，我们接下来将会详细讲解。
引用和参数
引入 PyTorch 模块和定义参数
```python
import torch
import torch.nn as nn
from torch.utils.data import Dataset, DataLoader
```
# 参数
```python
input_size = 5
output_size = 2
batch_size = 30
data_size = 100
```
设备
```python
device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")
```
实验（玩具）数据
生成一个玩具数据。你只需要实现 getitem.
```python
class RandomDataset(Dataset):
def __init__(self, size, length):
self.len = length
self.data = torch.randn(length, size)
def __getitem__(self, index):
return self.data[index]
def __len__(self):
return self.len
rand_loader = DataLoader(dataset=RandomDataset(input_size, data_size),batch_size=batch_size, shuffle=True)
```
简单模型
为了做一个小 demo，我们的模型只是获得一个输入，执行一个线性操作，然后给一个输出。尽管如此，你可以使用 DataParallel 在任何模型(CNN, RNN, Capsule Net 等等.)
我们放置了一个输出声明在模型中来检测输出和输入张量的大小。请注意在 batch rank 0 中的输出。
```python
class Model(nn.Module):
# Our model
def __init__(self, input_size, output_size):
super(Model, self).__init__()
self.fc = nn.Linear(input_size, output_size)
def forward(self, input):
output = self.fc(input)
print("\tIn Model: input size", input.size(),
"output size", output.size())
return output
```
创建模型并且数据并行处理
这是整个教程的核心。首先我们需要一个模型的实例，然后验证我们是否有多个 GPU。如果我们有多个 GPU，我们可以用 nn.DataParallel 来 包裹 我们的模型。然后我们使用 model.to(device) 把模型放到多 GPU 中。
```python
model = Model(input_size, output_size)
if torch.cuda.device_count() > 1:
print("Let's use", torch.cuda.device_count(), "GPUs!")
# dim = 0 [30, xxx] -> [10, ...], [10, ...], [10, ...] on 3 GPUs
model = nn.DataParallel(model)
model.to(device)
```
输出：
```python
Let's use 2 GPUs!
```
运行模型：
现在我们可以看到输入和输出张量的大小了。
```python
for data in rand_loader:
input = data.to(device)
output = model(input)
print("Outside: input size", input.size(),
"output_size", output.size())
```
输出：
<pre>In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2])
In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2])
Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2])
In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2])
In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2])
Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2])
In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2])
In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2])
Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2])
In Model: input size torch.Size([5, 5]) output size torch.Size([5, 2])
In Model: input size torch.Size([5, 5]) output size torch.Size([5, 2])
Outside: input size torch.Size([10, 5]) output_size torch.Size([10, 2])</pre>
结果：
如果你没有 GPU 或者只有一个 GPU，当我们获取 30 个输入和 30 个输出，模型将期望获得 30 个输入和 30 个输出。但是如果你有多个 GPU ，你会获得这样的结果。
多 GPU
如果你有 2 个GPU，你会看到：
<div id="gpus" class="section">
<pre><span class="c1"># on 2 GPUs</span>
<span class="n">Let</span><span class="s1">'s use 2 GPUs!</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">15</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">15</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">15</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">15</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">Outside</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output_size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">15</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">15</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">15</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">15</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">Outside</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output_size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">15</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">15</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">15</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">15</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">Outside</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output_size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">5</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">5</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">5</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">5</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">Outside</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output_size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span></pre>
</div>
如果你有 3个GPU，你会看到：
<pre><span class="n">Let</span><span class="s1">'s use 3 GPUs!</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">Outside</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output_size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">Outside</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output_size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">Outside</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output_size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">Outside</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output_size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span></pre>
如果你有 8个GPU，你会看到：
<pre><span class="n">Let</span><span class="s1">'s use 8 GPUs!</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">Outside</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output_size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">Outside</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output_size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">Outside</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output_size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">30</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">In</span> <span class="n">Model</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span>
<span class="n">Outside</span><span class="p">:</span> <span class="nb">input</span> <span class="n">size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="n">output_size</span> <span class="n">torch</span><span class="o">.</span><span class="n">Size</span><span class="p">([</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">])</span></pre>
<h2>总结</h2>
数据并行自动拆分了你的数据并且将任务单发送到多个 GPU 上。当每一个模型都完成自己的任务之后，DataParallel 收集并且合并这些结果，然后再返回给你。
更多信息，请访问：
https://pytorch.org/tutorials/beginner/former_torchies/parallelism_tutorial.html
下载 Python 版本完整代码：
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