torch-pruning 1.2.3

Towards Any Structural Pruning

Towards Any Structural Pruning

[Documentation & Tutorials] [FAQ]

Torch-Pruning (TP) is a library for structural pruning with the following features:

• General-purpose Pruning Toolkit: TP enables structural pruning for a wide range of deep neural networks, including Large Language Models (LLMs), Diffusion Models, Yolov7, yolov8, Vision Transformers, Swin Transformers, Bert, FasterRCNN, SSD, ResNe(X)t, ConvNext, DenseNet, ConvNext, RegNet, DeepLab, etc. Different from torch.nn.utils.prune that zeroizes parameters through masking, Torch-Pruning deploys a (non-deep) graph algorithm called DepGraph to remove parameters physically. Currently, TP is able to prune approximately 81/85=95.3% of the models from Torchvision 0.13.1. Try this Colab Demo for a quick start.
• Performance Benchmark: Reproduce the our results in the DepGraph paper.

For more technical details, please refer to our CVPR'23 paper:

DepGraph: Towards Any Structural Pruning
Gongfan Fang, Xinyin Ma, Mingli Song, Michael Bi Mi, Xinchao Wang
Learning and Vision Lab, National University of Singapore

Update:

• 2023.08.20 :rocket: Examples for Vision Transformers, Swin Transformers, Bert.
• 2023.07.19 :rocket: Support LLaMA, LLaMA-2, Vicuna, Baichuan in LLM-Pruner
• 2023.05.20 :rocket: LLM-Pruner: On the Structural Pruning of Large Language Models [arXiv]
• 2023.05.19 Structural Pruning for Diffusion Models [arXiv]
• 2023.04.15 Pruning and Post-training for YOLOv7 / YOLOv8

Features:

• High-level Pruners: MagnitudePruner, BNScalePruner, GroupNormPruner, GrowingRegPruner, RandomPruner, etc.
• Dependency Graph for automatic structural pruning
• Low-level pruning functions
• Supported Importance Criteria: L-p Norm, Taylor, Random, BNScaling, etc.
• Supported modules: Linear, (Transposed) Conv, Normalization, PReLU, Embedding, MultiheadAttention, nn.Parameters and customized modules.
• Supported operators: split, concatenation, skip connection, flatten, reshape, view, all element-wise ops, etc.
• Benchmarks and Tutorials

Contact Us:

Please do not hesitate to open a discussion or issue if you encounter any problems with the library or the paper.
Or Join our Discord or WeChat group for a chat:

• Discord: link
• WeChat (Group size exceeded 200): QR Code

Installation

Torch-Pruning is compatible with both PyTorch 1.x and 2.x versions. However, it is highly recommended to use PyTorch 1.12.1 or higher.

pip install torch-pruning 

or

git clone https://github.com/VainF/Torch-Pruning.git

Quickstart

Here we provide a quick start for Torch-Pruning. More explained details can be found in Tutorals

0. How It Works

In structural pruning, a "Group" is defined as the minimal unit that can be removed within deep networks. These groups are composed of multiple layers that are interdependent and need to be pruned together in order to maintain the integrity of the resulting structures. However, deep networks often have complex dependencies among their layers, making structural pruning a challenging task. This work addresses this challenge by introducing an automated mechanism called "DepGraph." DepGraph allows for seamless parameter grouping and facilitates pruning in various types of deep networks.

1. A Minimal Example

Please ensure that your model is set up to enable AutoGrad without something like torch.no_grad or .requires_grad=False.

import torch
from torchvision.models import resnet18
import torch_pruning as tp

model = resnet18(pretrained=True).eval()

# 1. Build dependency graph for resnet18
DG = tp.DependencyGraph().build_dependency(model, example_inputs=torch.randn(1,3,224,224))

# 2. Specify the to-be-pruned channels. Here we prune those channels indexed by [2, 6, 9].
group = DG.get_pruning_group( model.conv1, tp.prune_conv_out_channels, idxs=[2, 6, 9] )

# 3. Prune all grouped layers that are coupled with model.conv1 (included).
if DG.check_pruning_group(group): # avoid full pruning, i.e., channels=0.
    group.prune()
    
# 4. Save & Load
model.zero_grad() # reset gradients
torch.save(model, 'model.pth') # without .state_dict
model = torch.load('model.pth') # load the model object

The above example demonstrates the fundamental pruning pipeline utilizing DepGraph. The target layer resnet.conv1 is coupled with several layers, necessitating their simultaneous removal during structural pruning. To observe the cascading effect of pruning operations, we can print the groups and observe how one pruning operation can "trigger" others. In the subsequent outputs, "A => B" indicates that pruning operation "A" triggers pruning operation "B." The group[0] refers to the pruning root in DG.get_pruning_group.

--------------------------------
          Pruning Group
--------------------------------
[0] prune_out_channels on conv1 (Conv2d(3, 64, kernel_size=(7, 7), stride=(2, 2), padding=(3, 3), bias=False)) => prune_out_channels on conv1 (Conv2d(3, 64, kernel_size=(7, 7), stride=(2, 2), padding=(3, 3), bias=False)), idxs=[2, 6, 9] (Pruning Root)
[1] prune_out_channels on conv1 (Conv2d(3, 64, kernel_size=(7, 7), stride=(2, 2), padding=(3, 3), bias=False)) => prune_out_channels on bn1 (BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)), idxs=[2, 6, 9]
[2] prune_out_channels on bn1 (BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)) => prune_out_channels on _ElementWiseOp_20(ReluBackward0), idxs=[2, 6, 9]
[3] prune_out_channels on _ElementWiseOp_20(ReluBackward0) => prune_out_channels on _ElementWiseOp_19(MaxPool2DWithIndicesBackward0), idxs=[2, 6, 9]
[4] prune_out_channels on _ElementWiseOp_19(MaxPool2DWithIndicesBackward0) => prune_out_channels on _ElementWiseOp_18(AddBackward0), idxs=[2, 6, 9]
[5] prune_out_channels on _ElementWiseOp_19(MaxPool2DWithIndicesBackward0) => prune_in_channels on layer1.0.conv1 (Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)), idxs=[2, 6, 9]
[6] prune_out_channels on _ElementWiseOp_18(AddBackward0) => prune_out_channels on layer1.0.bn2 (BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)), idxs=[2, 6, 9]
[7] prune_out_channels on _ElementWiseOp_18(AddBackward0) => prune_out_channels on _ElementWiseOp_17(ReluBackward0), idxs=[2, 6, 9]
[8] prune_out_channels on _ElementWiseOp_17(ReluBackward0) => prune_out_channels on _ElementWiseOp_16(AddBackward0), idxs=[2, 6, 9]
[9] prune_out_channels on _ElementWiseOp_17(ReluBackward0) => prune_in_channels on layer1.1.conv1 (Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)), idxs=[2, 6, 9]
[10] prune_out_channels on _ElementWiseOp_16(AddBackward0) => prune_out_channels on layer1.1.bn2 (BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)), idxs=[2, 6, 9]
[11] prune_out_channels on _ElementWiseOp_16(AddBackward0) => prune_out_channels on _ElementWiseOp_15(ReluBackward0), idxs=[2, 6, 9]
[12] prune_out_channels on _ElementWiseOp_15(ReluBackward0) => prune_in_channels on layer2.0.downsample.0 (Conv2d(64, 128, kernel_size=(1, 1), stride=(2, 2), bias=False)), idxs=[2, 6, 9]
[13] prune_out_channels on _ElementWiseOp_15(ReluBackward0) => prune_in_channels on layer2.0.conv1 (Conv2d(64, 128, kernel_size=(3, 3), stride=(2, 2), padding=(1, 1), bias=False)), idxs=[2, 6, 9]
[14] prune_out_channels on layer1.1.bn2 (BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)) => prune_out_channels on layer1.1.conv2 (Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)), idxs=[2, 6, 9]
[15] prune_out_channels on layer1.0.bn2 (BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)) => prune_out_channels on layer1.0.conv2 (Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)), idxs=[2, 6, 9]
--------------------------------

For more details about grouping, please refer to Wiki - DepGraph & Group

How to scan all groups (Advanced):

We can use DG.get_all_groups(ignored_layers, root_module_types) to scan all groups sequentially. Each group will begin with a layer that matches a type in the "root_module_types" parameter. Note that DG.get_all_groups is only responsible for grouping and does not have any knowledge or understanding of which parameters should be pruned. Therefore, it is necessary to specify the pruning idxs using group.prune(idxs=idxs).

for group in DG.get_all_groups(ignored_layers=[model.conv1], root_module_types=[nn.Conv2d, nn.Linear]):
    # handle groups in sequential order
    idxs = [2,4,6] # your pruning indices
    group.prune(idxs=idxs)
    print(group)

2. High-level Pruners

Leveraging the DependencyGraph, we developed several high-level pruners in this repository to facilitate effortless pruning. By specifying the desired channel sparsity, the pruner will scan all prunable groups, prune the entire model, and fine-tune it using your own training code. For detailed information on this process, please refer to this tutorial, which shows how to implement a slimming pruner from scratch. Additionally, a more practical example is available in benchmarks/main.py.

import torch
from torchvision.models import resnet18
import torch_pruning as tp

model = resnet18(pretrained=True)

# Importance criteria
example_inputs = torch.randn(1, 3, 224, 224)
imp = tp.importance.TaylorImportance()

ignored_layers = []
for m in model.modules():
    if isinstance(m, torch.nn.Linear) and m.out_features == 1000:
        ignored_layers.append(m) # DO NOT prune the final classifier!

iterative_steps = 5 # progressive pruning
pruner = tp.pruner.MagnitudePruner(
    model,
    example_inputs,
    importance=imp,
    iterative_steps=iterative_steps,
    ch_sparsity=0.5, # remove 50% channels, ResNet18 = {64, 128, 256, 512} => ResNet18_Half = {32, 64, 128, 256}
    ignored_layers=ignored_layers,
)

base_macs, base_nparams = tp.utils.count_ops_and_params(model, example_inputs)
for i in range(iterative_steps):

    # Taylor expansion requires gradients for importance estimation
    if isinstance(imp, tp.importance.TaylorImportance):
        # A dummy loss, please replace it with your loss function and data!
        loss = model(example_inputs).sum() 
        loss.backward() # before pruner.step()

    pruner.step()
    macs, nparams = tp.utils.count_ops_and_params(model, example_inputs)
    # finetune your model here
    # finetune(model)
    # ...

Sparse Training

Some pruners like BNScalePruner and GroupNormPruner require sparse training before pruning. This can be easily achieved by inserting one line of code pruner.regularize(model) just after loss.backward() and before optimizer.step(). The pruner will update the gradient of trainable parameters.

for epoch in range(epochs):
    model.train()
    for i, (data, target) in enumerate(train_loader):
        data, target = data.to(device), target.to(device)
        optimizer.zero_grad()
        out = model(data)
        loss = F.cross_entropy(out, target)
        loss.backward() # after loss.backward()
        pruner.regularize(model) # <== for sparse training
        optimizer.step() # before optimizer.step()

Interactive Pruning (Advanced)

All high-level pruners offer support for interactive pruning. You can utilize the method "pruner.step(interactive=True)" to retrieve all the groups and interactively prune them by calling "group.prune()". This feature is particularly useful when you want to have control over or monitor the pruning process.

for i in range(iterative_steps):
    for group in pruner.step(interactive=True): # Warning: groups must be handled sequentially. Do not keep them as a list.
        print(group) 
        # do whatever you like with the group 
        dep, idxs = group[0] # get the idxs
        target_module = dep.target.module # get the root module
        pruning_fn = dep.handler # get the pruning function
        group.prune()
        # group.prune(idxs=[0, 2, 6]) # It is even possible to change the pruning behaviour with the idxs parameter
    macs, nparams = tp.utils.count_ops_and_params(model, example_inputs)
    # finetune your model here
    # finetune(model)
    # ...

Group-level Pruning

With DepGraph, it is easy to design some "group-level" criteria to estimate the importance of a whole group rather than a single layer. In Torch-pruning, all pruners work in the group level.

3. Save & Load

The following script saves the whole model object (structure+weights) as a 'model.pth'.

model.zero_grad() # Remove gradients
torch.save(model, 'model.pth') # without .state_dict
model = torch.load('model.pth') # load the pruned model

Experimental Features: Re-create pruned models from unpruned ones using tp.state_dict and tp.load_state_dict.

# save the pruned state_dict, which includes both pruned parameters and modified attributes
state_dict = tp.state_dict(pruned_model) # the pruned model, e.g., a resnet-18-half
torch.save(state_dict, 'pruned.pth')

# create a new model, e.g. resnet18
new_model = resnet18().eval()

# load the pruned state_dict into the unpruned model.
loaded_state_dict = torch.load('pruned.pth', map_location='cpu')
tp.load_state_dict(new_model, state_dict=loaded_state_dict)

Refer to tests/test_serialization.py for an ViT example. In this example, we will prune the model and modify some attributes like model.hidden_dims.

4. Low-level Pruning Functions

Although it is possible to manually prune your model using low-level functions, this approach can be cumbersome and time-consuming due to the need for meticulous management of dependencies. Therefore, we strongly recommend utilizing the high-level pruners mentioned earlier to streamline and simplify the pruning process. These pruners provide a more convenient and efficient way to perform pruning on your models. To manually prune the model.conv1 of a ResNet-18, the pruning pipeline should look like this:

tp.prune_conv_out_channels( model.conv1, idxs=[2,6,9] )

# fix the broken dependencies manually
tp.prune_batchnorm_out_channels( model.bn1, idxs=[2,6,9] )
tp.prune_conv_in_channels( model.layer2[0].conv1, idxs=[2,6,9] )
...

The following pruning functions are available:

'prune_conv_out_channels',
'prune_conv_in_channels',
'prune_depthwise_conv_out_channels',
'prune_depthwise_conv_in_channels',
'prune_batchnorm_out_channels',
'prune_batchnorm_in_channels',
'prune_linear_out_channels',
'prune_linear_in_channels',
'prune_prelu_out_channels',
'prune_prelu_in_channels',
'prune_layernorm_out_channels',
'prune_layernorm_in_channels',
'prune_embedding_out_channels',
'prune_embedding_in_channels',
'prune_parameter_out_channels',
'prune_parameter_in_channels',
'prune_multihead_attention_out_channels',
'prune_multihead_attention_in_channels',
'prune_groupnorm_out_channels',
'prune_groupnorm_in_channels',
'prune_instancenorm_out_channels',
'prune_instancenorm_in_channels',

5. Customized Layers

Please refer to examples/hf_transformers/prune_swin.py, which implements a new pruner for the customized module SwinPatchMerging. A more simple example is available at tests/test_customized_layer.py.

6. Benchmarks

Our results on {ResNet-56 / CIFAR-10 / 2.00x}

Method	Base (%)	Pruned (%)	$\Delta$ Acc (%)	Speed Up
NIPS [1]	-	-	-0.03	1.76x
Geometric [2]	93.59	93.26	-0.33	1.70x
Polar [3]	93.80	93.83	+0.03	1.88x
CP [4]	92.80	91.80	-1.00	2.00x
AMC [5]	92.80	91.90	-0.90	2.00x
HRank [6]	93.26	92.17	-0.09	2.00x
SFP [7]	93.59	93.36	+0.23	2.11x
ResRep [8]	93.71	93.71	+0.00	2.12x
Ours-L1	93.53	92.93	-0.60	2.12x
Ours-BN	93.53	93.29	-0.24	2.12x
Ours-Group	93.53	93.77	+0.38	2.13x

Latency

Latency test on ResNet-50, Batch Size=64.

[Iter 0]        Sparsity: 0.00,         MACs: 4.12 G,   Params: 25.56 M,        Latency: 45.22 ms +- 0.03 ms
[Iter 1]        Sparsity: 0.05,         MACs: 3.68 G,   Params: 22.97 M,        Latency: 46.53 ms +- 0.06 ms
[Iter 2]        Sparsity: 0.10,         MACs: 3.31 G,   Params: 20.63 M,        Latency: 43.85 ms +- 0.08 ms
[Iter 3]        Sparsity: 0.15,         MACs: 2.97 G,   Params: 18.36 M,        Latency: 41.22 ms +- 0.10 ms
[Iter 4]        Sparsity: 0.20,         MACs: 2.63 G,   Params: 16.27 M,        Latency: 39.28 ms +- 0.20 ms
[Iter 5]        Sparsity: 0.25,         MACs: 2.35 G,   Params: 14.39 M,        Latency: 34.60 ms +- 0.19 ms
[Iter 6]        Sparsity: 0.30,         MACs: 2.02 G,   Params: 12.46 M,        Latency: 33.38 ms +- 0.27 ms
[Iter 7]        Sparsity: 0.35,         MACs: 1.74 G,   Params: 10.75 M,        Latency: 31.46 ms +- 0.20 ms
[Iter 8]        Sparsity: 0.40,         MACs: 1.50 G,   Params: 9.14 M,         Latency: 29.04 ms +- 0.19 ms
[Iter 9]        Sparsity: 0.45,         MACs: 1.26 G,   Params: 7.68 M,         Latency: 27.47 ms +- 0.28 ms
[Iter 10]       Sparsity: 0.50,         MACs: 1.07 G,   Params: 6.41 M,         Latency: 20.68 ms +- 0.13 ms
[Iter 11]       Sparsity: 0.55,         MACs: 0.85 G,   Params: 5.14 M,         Latency: 20.48 ms +- 0.21 ms
[Iter 12]       Sparsity: 0.60,         MACs: 0.67 G,   Params: 4.07 M,         Latency: 18.12 ms +- 0.15 ms
[Iter 13]       Sparsity: 0.65,         MACs: 0.53 G,   Params: 3.10 M,         Latency: 15.19 ms +- 0.01 ms
[Iter 14]       Sparsity: 0.70,         MACs: 0.39 G,   Params: 2.28 M,         Latency: 13.47 ms +- 0.01 ms
[Iter 15]       Sparsity: 0.75,         MACs: 0.29 G,   Params: 1.61 M,         Latency: 10.07 ms +- 0.01 ms
[Iter 16]       Sparsity: 0.80,         MACs: 0.18 G,   Params: 1.01 M,         Latency: 8.96 ms +- 0.02 ms
[Iter 17]       Sparsity: 0.85,         MACs: 0.10 G,   Params: 0.57 M,         Latency: 7.03 ms +- 0.04 ms
[Iter 18]       Sparsity: 0.90,         MACs: 0.05 G,   Params: 0.25 M,         Latency: 5.81 ms +- 0.03 ms
[Iter 19]       Sparsity: 0.95,         MACs: 0.01 G,   Params: 0.06 M,         Latency: 5.70 ms +- 0.03 ms
[Iter 20]       Sparsity: 1.00,         MACs: 0.01 G,   Params: 0.06 M,         Latency: 5.71 ms +- 0.03 ms

Please refer to benchmarks for more details.

8. Series of Works

DepGraph: Towards Any Structural Pruning [Project] [Paper]
Gongfan Fang, Xinyin Ma, Mingli Song, Michael Bi Mi, Xinchao Wang

LLM-Pruner: On the Structural Pruning of Large Language Models [Project] [arXiv]
Xinyin Ma, Gongfan Fang, Xinchao Wang

Structural Pruning for Diffusion Models [Project] [arxiv]
Gongfan Fang, Xinyin Ma, Xinchao Wang

Citation

@inproceedings{fang2023depgraph,
  title={Depgraph: Towards any structural pruning},
  author={Fang, Gongfan and Ma, Xinyin and Song, Mingli and Mi, Michael Bi and Wang, Xinchao},
  booktitle={Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition},
  pages={16091--16101},
  year={2023}
}