參考:
https://pytorch.org/docs/stable/nn.html
https://github.com/apachecn/pytorch-doc-zh/blob/master/docs/1.0/blitz_data_parallel_tutorial.md
一、 torch.nn.DataParallel
torch.nn.
DataParallel
(module, device_ids=None, output_device=None, dim=0)
在正向傳遞中,模塊在每個設備上覆制,每個副本處理一部分輸入。在向後傳遞期間,來自每個副本的漸變被加到原始模塊中。
- module:需要並行處理的模型
- device_ids:並行處理的設備,默認使用所有的cuda
- output_device:輸出的位置,默認輸出到cuda:0
例子:
>>> net = torch.nn.DataParallel(model, device_ids=[0, 1, 2])
>>> output = net(input_var) # input_var can be on any device, including CPU
torch.nn.DataParallel()返回一個新的模型,能夠將輸入數據自動分配到所使用的GPU上。所以輸入數據的數量應該大於所使用的設備的數量。
二、一個完整例子
import torch
import torch.nn as nn
from torch.utils.data import Dataset, DataLoader
# parameters and DataLoaders
input_size = 5
output_size = 2
batch_size = 30
data_size = 100
device = torch.device('cuda:0' if torch.cuda.is_available() else 'cpu')
# 隨機數據集
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)
# 以簡單模型爲例,同樣可以用於CNN, RNN 等複雜模型
class Model(nn.Module):
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('In model: input size', input.size(), 'output size:', output.size())
return output
# 實例
model = Model(input_size, output_size)
if torch.cuda.device_count() > 1:
print("Use", torch.cuda.device_count(), 'gpus')
model = nn.DataParallel(model)
model.to(device)
for data in rand_loader:
input = data.to(device)
output = model(input)
print('Outside: input size ', input.size(), 'output size: ', output.size())
輸出:
In model: input size torch.Size([30, 5]) output size: torch.Size([30, 2])
Outside: input size torch.Size([30, 5]) output size: torch.Size([30, 2])
In model: input size torch.Size([30, 5]) output size: torch.Size([30, 2])
Outside: input size torch.Size([30, 5]) output size: torch.Size([30, 2])
In model: input size torch.Size([30, 5]) output size: torch.Size([30, 2])
Outside: input size torch.Size([30, 5]) output size: torch.Size([30, 2])
In model: input size torch.Size([10, 5]) output size: torch.Size([10, 2])
Outside: input size torch.Size([10, 5]) output size: torch.Size([10, 2])
若有2個GPU
Use 2 GPUs! 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])
若有3個GPU
Use 3 GPUs! In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2]) In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2]) In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2]) Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2]) In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2]) In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2]) In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2]) Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2]) In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2]) In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2]) In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2]) Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2]) In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2]) In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2]) In Model: input size torch.Size([2, 5]) output size torch.Size([2, 2]) Outside: input size torch.Size([10, 5]) output_size torch.Size([10, 2])
總結:
DataParallel
自動的劃分數據,並將作業發送到多個GPU上的多個模型。DataParallel
會在每個模型完成作業後,收集與合併結果然後返回給你。