主要为了测试模型增加Lora模块后，参数量和训练速度的变化情况。
结论：正常情况下，增加Lora模块是会增加参数量的，因此前向传播和反向传播的时间也会增加。
但是，在大语言模型训练的情况下，因为基础模型本身参数量非常大，Lora模块增加的参数量相对非常小。并且，基础模型不参与梯度更新，可以做模型量化，实际上是能减少模型训练时间和显存使用量的。
以下是实验脚本和运行结果：
import time
import torch
from torch import nn
from peft import LoraConfig, get_peft_model, PeftModel
from torchsummary import summary
x_train = torch.randn((1000, 10))
y_train = torch.randn((1000, 1))
net = nn.Sequential(
nn.Linear(10,20),
nn.Sigmoid(),
nn.Linear(20,30),
nn.Sigmoid(),
nn.Linear(30,1)
)
summary(net, (1,10))
config = LoraConfig(target_modules=["0"], r=2)
model = get_peft_model(net, config)
criterion = torch.nn.MSELoss(reduction='mean') # 定义损失函数，采用均方误差
optimizer = torch.optim.Adam(model.parameters(), lr=0.3) # 定义优化器，采用Adam
summary(model, (1,10))
# base 前向计算时间
start = time.time()
for i in range(100000):
y_pre = net(x_train) # 前向传播
print("base 前向计算时间: ", time.time() - start)
# lora 前向计算时间
start = time.time()
for i in range(100000):
y_pre = model(x_train) # 前向传播
print("lora 前向计算时间", time.time() - start)
# base 反向传播时间
start = time.time()
for i in range(1000):
y_pre = net(x_train) # 前向传播
loss = criterion(y_pre, y_train) # 计算损失
optimizer.zero_grad() # 梯度清零
loss.backward() # 反向传播
optimizer.step() # 使用优化器更新梯度
print("base loss after training: ", loss.item())
print("base 反向计算时间", time.time() - start)
# lora 反向传播时间
start = time.time()
for i in range(1000):
y_pre = model(x_train) # 前向传播
loss = criterion(y_pre, y_train) # 计算损失
optimizer.zero_grad() # 梯度清零
loss.backward() # 反向传播
optimizer.step() # 使用优化器更新梯度
print("lora loss after training: ", loss.item())
print("lora 反向计算时间", time.time() - start)
运行代码输出：
---------------------------------------------------------------- Layer (type) Output Shape Param # ================================================================ Linear-1 [-1, 1, 20] 220 Sigmoid-2 [-1, 1, 20] 0 Linear-3 [-1, 1, 30] 630 Sigmoid-4 [-1, 1, 30] 0 Linear-5 [-1, 1, 1] 31 ================================================================ Total params: 881 Trainable params: 881 Non-trainable params: 0 ---------------------------------------------------------------- Input size (MB): 0.00 Forward/backward pass size (MB): 0.00 Params size (MB): 0.00 Estimated Total Size (MB): 0.00 ---------------------------------------------------------------- ---------------------------------------------------------------- Layer (type) Output Shape Param # ================================================================ Linear-1 [-1, 1, 20] 220 Identity-2 [-1, 1, 10] 0 Linear-3 [-1, 1, 2] 20 Linear-4 [-1, 1, 20] 40 Linear-5 [-1, 1, 20] 220 Sigmoid-6 [-1, 1, 20] 0 Linear-7 [-1, 1, 30] 630 Sigmoid-8 [-1, 1, 30] 0 Linear-9 [-1, 1, 1] 31 ================================================================ Total params: 1,161 Trainable params: 60 Non-trainable params: 1,101 ---------------------------------------------------------------- Input size (MB): 0.00 Forward/backward pass size (MB): 0.00 Params size (MB): 0.00 Estimated Total Size (MB): 0.01 ---------------------------------------------------------------- base loss after training: 1.0724023580551147 base 反向计算时间 2.9570980072021484 lora loss after training: 1.0643658638000488 lora 反向计算时间 3.053032159805298
#部分参考https://zhuanlan.zhihu.com/p/666000885
