normal_prune.py

from models import *
from utils.utils import *
import torch
import numpy as np
from copy import deepcopy
from test import test
from terminaltables import AsciiTable
import time
from utils.utils import *
from utils.prune_utils import *
import os

os.environ["CUDA_VISIBLE_DEVICES"] = '3'

class opt():
    model_def = "cfg/ghost32-yolov3-visdrone.cfg"
    data_config = "data/visdrone.data"
    model = 'weights/best/best.pt'


#指定GPU
#torch.cuda.set_device(2)
percent = 0.6

device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
model = Darknet(opt.model_def).to(device)

if opt.model:
    if opt.model.endswith(".pt"):
        model.load_state_dict(torch.load(opt.model, map_location=device)['model'])
    else:
        _ = load_darknet_weights(model, opt.model)
        

data_config = parse_data_cfg(opt.data_config)

valid_path = data_config["valid"]
class_names = load_classes(data_config["names"])


eval_model = lambda model:test(model=model, imgsz=640, cfg='cfg/ghost-yolov3-visdrone.cfg', data='data/visdrone.data')



obtain_num_parameters = lambda model:sum([param.nelement() for param in model.parameters()])

#这个不应该注释掉，等会要恢复
with torch.no_grad():
    origin_model_metric = eval_model(model)
    #results, maps = test.test(cfg=opt.model_def,
                              #data=opt.data_config,
                              #batch_size=4,
                              #img_sz=608,
                              #model=ema.ema,
                              #conf_thres=0.001
                              #save_json=False,
                              #single_cls=False,

                              
origin_nparameters = obtain_num_parameters(model)

CBL_idx, Conv_idx, prune_idx= parse_module_defs(model.module_defs)


#将所有要剪枝的BN层的α参数，拷贝到bn_weights列表
bn_weights = gather_bn_weights(model.module_list, prune_idx)

#torch.sort返回二维列表，第一维是排序后的值列表，第二维是排序后的值列表对应的索引
sorted_bn = torch.sort(bn_weights)[0]


#避免剪掉所有channel的最高阈值(每个BN层的gamma的最大值的最小值即为阈值上限)
highest_thre = []
for idx in prune_idx:
    #.item()可以得到张量里的元素值
    highest_thre.append(model.module_list[idx][1].weight.data.abs().max().item())
highest_thre = min(highest_thre)

# 找到highest_thre对应的下标对应的百分比
percent_limit = (sorted_bn==highest_thre).nonzero().item()/len(bn_weights)

print(f'Threshold should be less than {highest_thre:.4f}.')
print(f'The corresponding prune ratio is {percent_limit:.3f}.')


# 该函数有很重要的意义：
# ①先用深拷贝将原始模型拷贝下来，得到model_copy
# ②将model_copy中，BN层中低于阈值的α参数赋值为0
# ③在BN层中，输出y=α*x+β，由于α参数的值被赋值为0，因此输入仅加了一个偏置β
# ④很神奇的是，network slimming中是将α参数和β参数都置0，该处只将α参数置0，但效果却很好：其实在另外一篇论文中，已经提到，可以先将β参数的效果移到
# 下一层卷积层，再去剪掉本层的α参数

# 该函数用最简单的方法，让我们看到了，如何快速看到剪枝后的效果



def prune_and_eval(model, sorted_bn, percent=.0):
    model_copy = deepcopy(model)
    thre_index = int(len(sorted_bn) * percent)
    #获得α参数的阈值，小于该值的α参数对应的通道，全部裁剪掉
    thre = sorted_bn[thre_index]

    print(f'Channels with Gamma value less than {thre:.4f} are pruned!')

    remain_num = 0
    for idx in prune_idx:

        bn_module = model_copy.module_list[idx][1]

        mask = obtain_bn_mask(bn_module, thre)

        remain_num += int(mask.sum())
        bn_module.weight.data.mul_(mask)
    with torch.no_grad():
        mAP = eval_model(model_copy)[1].mean()

    print(f'Number of channels has been reduced from {len(sorted_bn)} to {remain_num}')
    print(f'Prune ratio: {1-remain_num/len(sorted_bn):.3f}')
    print(f'mAP of the pruned model is {mAP:.4f}')

    return thre


threshold = prune_and_eval(model, sorted_bn, percent)



#****************************************************************
#虽然上面已经能看到剪枝后的效果，但是没有生成剪枝后的模型结构，因此下面的代码是为了生成新的模型结构并拷贝旧模型参数到新模型


#%%
def obtain_filters_mask(model, thre, CBL_idx, prune_idx):

    pruned = 0
    total = 0
    num_filters = []
    filters_mask = []
    #CBL_idx存储的是所有带BN的卷积层（YOLO层的前一层卷积层是不带BN的）
    for idx in CBL_idx:
        bn_module = model.module_list[idx][1]
        if idx in prune_idx:

            mask = obtain_bn_mask(bn_module, thre).cpu().numpy()
            remain = int(mask.sum())
            pruned = pruned + mask.shape[0] - remain

            if remain == 0:
                print("Channels would be all pruned!")
                raise Exception

            print(f'layer index: {idx:>3d} \t total channel: {mask.shape[0]:>4d} \t '
                  f'remaining channel: {remain:>4d}')
        else:
            mask = np.ones(bn_module.weight.data.shape)
            remain = mask.shape[0]

        total += mask.shape[0]
        num_filters.append(remain)
        filters_mask.append(mask.copy())

    #因此，这里求出的prune_ratio,需要裁剪的α参数/cbl_idx中所有的α参数
    prune_ratio = pruned / total
    print(f'Prune channels: {pruned}\tPrune ratio: {prune_ratio:.3f}')

    return num_filters, filters_mask

num_filters, filters_mask = obtain_filters_mask(model, threshold, CBL_idx, prune_idx)


#CBLidx2mask存储CBL_idx中，每一层BN层对应的mask
CBLidx2mask = {idx: mask for idx, mask in zip(CBL_idx, filters_mask)}

pruned_model = prune_model_keep_size(model, prune_idx, CBL_idx, CBLidx2mask)




with torch.no_grad():
    mAP = eval_model(pruned_model)[1].mean()
print('after prune_model_keep_size map is {}'.format(mAP))


#获得原始模型的module_defs，并修改该defs中的卷积核数量
compact_module_defs = deepcopy(model.module_defs)
for idx, num in zip(CBL_idx, num_filters):
    assert compact_module_defs[idx]['type'] == 'convolutional'
    compact_module_defs[idx]['filters'] = str(num)



#compact_model = Darknet([model.hyp.copy()] + compact_module_defs).to(device)
for i, mdef in enumerate(compact_module_defs):
    if mdef['type'] == 'shortcut':
        mdef['from'] = str(mdef['from'][0])
    if mdef['type'] == 'route':
        if len(mdef['layers']) == 2 :
            mdef['layers'] = str(mdef['layers'][0]) + ',' + str(mdef['layers'][1])
        else:
            mdef['layers'] = str(mdef['layers'][0])
    if mdef['type'] == 'yolo':
        mdef['mask'] = str(mdef['mask'][0]) + ',' + str(mdef['mask'][1]) + ',' + str(mdef['mask'][2])
        mdef['anchors'] = '4,5,  6,10,  14,9,  11,18,  25,15,  21,30,  47,26,  37,53,  87,65'

pruned_cfg_file = write_cfg('pruned.cfg',  [model.hyper.copy()] + compact_module_defs)

compact_model = Darknet('pruned.cfg').to(device)
print(compact_model)
compact_nparameters = obtain_num_parameters(compact_model)

init_weights_from_loose_model(compact_model, pruned_model, CBL_idx, Conv_idx, CBLidx2mask)

random_input = torch.rand((16, 3, 416, 416)).to(device)

def obtain_avg_forward_time(input, model, repeat=200):

    model.eval()
    start = time.time()
    with torch.no_grad():
        for i in range(repeat):
            output = model(input)
    avg_infer_time = (time.time() - start) / repeat

    return avg_infer_time, output

pruned_forward_time, pruned_output = obtain_avg_forward_time(random_input, pruned_model)
compact_forward_time, compact_output = obtain_avg_forward_time(random_input, compact_model)



# 在测试集上测试剪枝后的模型, 并统计模型的参数数量
with torch.no_grad():
    compact_model_metric = eval_model(compact_model)


# 比较剪枝前后参数数量的变化、指标性能的变化
metric_table = [
    ["Metric", "Before", "After"],
    ["mAP", f'{origin_model_metric[1].mean():.6f}', f'{compact_model_metric[1].mean():.6f}'],
    ["Parameters", f"{origin_nparameters}", f"{compact_nparameters}"],
    ["Inference", f'{pruned_forward_time:.4f}', f'{compact_forward_time:.4f}']
]
print(AsciiTable(metric_table).table)



# 生成剪枝后的cfg文件并保存模型
pruned_cfg_name = opt.model_def.replace('/', f'/prune_{percent}_')

#由于原始的compact_module_defs将anchor从字符串变为了数组，因此这里将anchors重新变为字符串


#compact_model_name = opt.model.replace('/', f'/prune_{percent}_')
compact_model_name = 'weights/yolov3_visdrone_normal_pruning_'+str(percent)+'percent.weights'

save_weights(compact_model, path=compact_model_name)
print(f'Compact model has been saved: {compact_model_name}')