本文主要是介绍torch.fx量化——以cifar10数据集为例，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
1. 构建需要量化的模型
talk is cheap， show me the code
import torch
import torch.nn as nn
import torch.nn.functional as F
import copy
import torchvision
from torchvision import transforms
from torchvision.models.resnet import resnet50, resnet18
from torch.quantization.quantize_fx import prepare_fx, convert_fx
from torch.ao.quantization.fx.graph_module import ObservedGraphModule
from torch.quantization import (get_default_qconfig,
)
from torch import optim
import os
import timedef train_model(model, train_loader, test_loader, device):# The training configurations were not carefully selected.learning_rate = 1e-2num_epochs = 20criterion = nn.CrossEntropyLoss()model.to(device)# It seems that SGD optimizer is better than Adam optimizer for ResNet18 training on CIFAR10.optimizer = optim.SGD(model.parameters(), lr=learning_rate, momentum=0.9, weight_decay=1e-5)# optimizer = optim.Adam(model.parameters(), lr=learning_rate, betas=(0.9, 0.999), eps=1e-08, weight_decay=0, amsgrad=False)for epoch in range(num_epochs):# Trainingmodel.train()running_loss = 0running_corrects = 0for inputs, labels in train_loader:inputs = inputs.to(device)labels = labels.to(device)# zero the parameter gradientsoptimizer.zero_grad()# forward + backward + optimizeoutputs = model(inputs)_, preds = torch.max(outputs, 1)loss = criterion(outputs, labels)loss.backward()optimizer.step()# statisticsrunning_loss += loss.item() * inputs.size(0)running_corrects += torch.sum(preds == labels.data)train_loss = running_loss / len(train_loader.dataset)train_accuracy = running_corrects / len(train_loader.dataset)# Evaluationmodel.eval()eval_loss, eval_accuracy = evaluate_model(model=model, test_loader=test_loader, device=device, criterion=criterion)print("Epoch: {:02d} Train Loss: {:.3f} Train Acc: {:.3f} Eval Loss: {:.3f} Eval Acc: {:.3f}".format(epoch, train_loss, train_accuracy, eval_loss, eval_accuracy))return modeldef prepare_dataloader(num_workers=8, train_batch_size=128, eval_batch_size=256):train_transform = transforms.Compose([transforms.RandomCrop(32, padding=4),transforms.RandomHorizontalFlip(),transforms.ToTensor(),transforms.Normalize((0.4914, 0.4822, 0.4465), (0.2023, 0.1994, 0.2010)),])test_transform = transforms.Compose([transforms.ToTensor(),transforms.Normalize((0.4914, 0.4822, 0.4465), (0.2023, 0.1994, 0.2010)),])train_set = torchvision.datasets.CIFAR10(root="data", train=True, download=True, transform=train_transform)# We will use test set for validation and test in this project.# Do not use test set for validation in practice!test_set = torchvision.datasets.CIFAR10(root="data", train=False, download=True, transform=test_transform)train_sampler = torch.utils.data.RandomSampler(train_set)test_sampler = torch.utils.data.SequentialSampler(test_set)train_loader = torch.utils.data.DataLoader(dataset=train_set,batch_size=train_batch_size,sampler=train_sampler,num_workers=num_workers,)test_loader = torch.utils.data.DataLoader(dataset=test_set,batch_size=eval_batch_size,sampler=test_sampler,num_workers=num_workers,)return train_loader, test_loaderif __name__ == "__main__":train_loader, test_loader = prepare_dataloader()# first finetune model on cifar, we don't have imagnet so using cifar as testmodel = resnet18(pretrained=True)model.fc = nn.Linear(512, 10)if os.path.exists("r18_row.pth"):model.load_state_dict(torch.load("r18_row.pth", map_location="cpu"))else:train_model(model, train_loader, test_loader, torch.device("cuda"))print("train finished.")torch.save(model.state_dict(), "r18_row.pth")2. 编写模型量化代码
def quant_fx(model):model.eval()qconfig = get_default_qconfig("fbgemm")qconfig_dict = {"": qconfig,# 'object_type': []}model_to_quantize = copy.deepcopy(model)prepared_model = prepare_fx(model_to_quantize, qconfig_dict)print("prepared model: ", prepared_model)quantized_model = convert_fx(prepared_model)print("quantized model: ", quantized_model)torch.save(model.state_dict(), "r18.pth")torch.save(quantized_model.state_dict(), "r18_quant.pth")
我们做一个evaluation，来验证一下，在不校准的情况下，精度如何：
def evaluate_model(model, test_loader, device=torch.device("cpu"), criterion=None):t0 = time.time()model.eval()model.to(device)running_loss = 0running_corrects = 0for inputs, labels in test_loader:inputs = inputs.to(device)labels = labels.to(device)outputs = model(inputs)_, preds = torch.max(outputs, 1)if criterion is not None:loss = criterion(outputs, labels).item()else:loss = 0# statisticsrunning_loss += loss * inputs.size(0)running_corrects += torch.sum(preds == labels.data)eval_loss = running_loss / len(test_loader.dataset)eval_accuracy = running_corrects / len(test_loader.dataset)t1 = time.time()print(f"eval loss: {eval_loss}, eval acc: {eval_accuracy}, cost: {t1 - t0}")return eval_loss, eval_accuracy
evaluation结果：
量化前：eval loss: 0.0, eval acc: 0.8476999998092651, cost: 2.8914074897766113
量化后（未校准）：eval loss: 0.0, eval acc: 0.15240000188350677, cost: 1.240293264389038
可以看到，精度下降严重。此时需要进行一下校准。
3. 编写校准函数代码
def calib_quant_model(model, calib_dataloader):assert isinstance(model, ObservedGraphModule), "model must be a perpared fx ObservedGraphModule."model.eval()with torch.inference_mode():for inputs, labels in calib_dataloader:model(inputs)print("calib done.")
再次eval一下
def quant_calib_and_eval(model):# test only on CPUmodel.to(torch.device("cpu"))model.eval()qconfig = get_default_qconfig("fbgemm")qconfig_dict = {"": qconfig,# 'object_type': []}model2 = copy.deepcopy(model)model_prepared = prepare_fx(model2, qconfig_dict)model_int8 = convert_fx(model_prepared)model_int8.load_state_dict(torch.load("r18_quant.pth"))model_int8.eval()a = torch.randn([1, 3, 224, 224])o1 = model(a)o2 = model_int8(a)diff = torch.allclose(o1, o2, 1e-4)print(diff)print(o1.shape, o2.shape)print(o1, o2)get_output_from_logits(o1)get_output_from_logits(o2)train_loader, test_loader = prepare_dataloader()evaluate_model(model, test_loader)evaluate_model(model_int8, test_loader)# calib quant modelmodel2 = copy.deepcopy(model)model_prepared = prepare_fx(model2, qconfig_dict)model_int8 = convert_fx(model_prepared)torch.save(model_int8.state_dict(), "r18.pth")model_int8.eval()model_prepared = prepare_fx(model2, qconfig_dict)calib_quant_model(model_prepared, test_loader)model_int8 = convert_fx(model_prepared)torch.save(model_int8.state_dict(), "r18_quant_calib.pth")evaluate_model(model_int8, test_loader)
量化前： eval loss: 0.0, eval acc: 0.8476999998092651, cost: 2.8914074897766113
量化后（未校准）eval loss: 0.0, eval acc: 0.15240000188350677, cost: 1.240293264389038
calib done.
量化后（已校准）eval loss: 0.0, eval acc: 0.8442999720573425, cost: 1.2966759204864502
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