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Searching for Efficient Multi-Stage Vision Transformers

This repository contains the official Pytorch implementation of "Searching for Efficient Multi-Stage Vision Transformers" and is based on DeiT and timm.

<img src="fig/vit_res.png" alt="photo not available" width="80%" height="80%"> Illustration of the proposed multi-stage ViT-Res network. <img src="fig/nas_overview.png" alt="photo not available" width="80%" height="80%"> Illustration of weight-sharing neural architecture search with multi-architectural sampling. <img src="fig/acc_mac.png" alt="photo not available" width="40%" height="40%"> Accuracy-MACs trade-offs of the proposed ViT-ResNAS. Our networks achieves comparable results to previous work.

Requirements

The codebase is tested with 8 V100 (16GB) GPUs.

To install requirements:

    pip install -r requirements.txt

Docker files are provided to set up the environment. Please run:

    cd docker

    sh 1_env_setup.sh
    
    sh 2_build_docker_image.sh
    
    sh 3_run_docker_image.sh

Make sure that the configuration specified in 3_run_docker_image.sh is correct before running the command.

Data Preparation

Download and extract ImageNet train and val images from http://image-net.org/. The directory structure is the standard layout for the torchvision datasets.ImageFolder, and the training and validation data is expected to be in the train/ folder and val folder respectively:

/path/to/imagenet/
  train/
    class1/
      img1.jpeg
    class2/
      img2.jpeg
  val/
    class1/
      img3.jpeg
    class/2
      img4.jpeg

Pre-Trained Models

Pre-trained weights of super-networks and searched networks can be found here.

Training ViT-Res

To train ViT-Res-Tiny, modify IMAGENET_PATH in scripts/vit-sr-nas/reference_net/tiny.sh and run:

    sh scripts/vit-sr-nas/reference_net/tiny.sh

We use 8 GPUs for training. Please modify numbers of GPUs (--nproc_per_node) and adjust batch size (--batch-size) if different numbers of GPUs are used.

Performing Neural Architecture Search

0. Building Sub-Train and Sub-Val Set

Modify _SOURCE_DIR, _SUB_TRAIN_DIR, and _SUB_VAL_DIR in search_utils/build_subset.py, and run:

    cd search_utils
    
    python build_subset.py
    
    cd ..

1. Super-Network Training

Before running each script, modify IMAGENET_PATH (directed to the directory containing the sub-train and sub-val sets).

For ViT-ResNAS-Tiny, run:

    sh scripts/vit-sr-nas/super_net/tiny.sh

For ViT-ResNAS-Small and Medium, run:

    sh scripts/vit-sr-nas/super_net/small.sh

2. Evolutionary Search

Before running each script, modify IMAGENET_PATH (directed to the directory containing the sub-train and sub-val sets) and MODEL_PATH.

For ViT-ResNAS-Tiny, run:

    sh scripts/vit-sr-nas/evolutionary_search/tiny.sh

For ViT-ResNAS-Small, run:

    sh scripts/vit-sr-nas/evolutionary_search/small_mac@2.9G.sh

For ViT-ResNAS-Medium, run:

    sh scripts/vit-sr-nas/evolutionary_search/medium_mac@4.6G.sh

After running evolutionary search for each network, see summary.txt in output directory and modify network_def.

For example, the network_def in summary.txt is ((4, 220), (1, (220, 5, 32), (220, 880), 1), (1, (220, 5, 32), (220, 880), 1), (1, (220, 7, 32), (220, 800), 1), (1, (220, 7, 32), (220, 800), 0), (1, (220, 5, 32), (220, 720), 1), (1, (220, 5, 32), (220, 720), 1), (1, (220, 5, 32), (220, 720), 1), (3, 220, 440), (1, (440, 10, 48), (440, 1760), 1), (1, (440, 10, 48), (440, 1440), 1), (1, (440, 10, 48), (440, 1920), 1), (1, (440, 10, 48), (440, 1600), 1), (1, (440, 12, 48), (440, 1600), 1), (1, (440, 12, 48), (440, 1120), 0), (1, (440, 12, 48), (440, 1440), 1), (3, 440, 880), (1, (880, 16, 64), (880, 3200), 1), (1, (880, 12, 64), (880, 3200), 1), (1, (880, 16, 64), (880, 2880), 1), (1, (880, 12, 64), (880, 3200), 0), (1, (880, 12, 64), (880, 2240), 1), (1, (880, 12, 64), (880, 3520), 0), (1, (880, 14, 64), (880, 2560), 1), (2, 880, 1000)).

Remove the element in the tuple that has 1 in the first element and 0 in the last element (e.g. (1, (220, 5, 32), (220, 880), 0)).

This reflects that the transformer block is removed in a searched network.

After this modification, the network_def becomes ((4, 220), (1, (220, 5, 32), (220, 880), 1), (1, (220, 5, 32), (220, 880), 1), (1, (220, 7, 32), (220, 800), 1), (1, (220, 5, 32), (220, 720), 1), (1, (220, 5, 32), (220, 720), 1), (1, (220, 5, 32), (220, 720), 1), (3, 220, 440), (1, (440, 10, 48), (440, 1760), 1), (1, (440, 10, 48), (440, 1440), 1), (1, (440, 10, 48), (440, 1920), 1), (1, (440, 10, 48), (440, 1600), 1), (1, (440, 12, 48), (440, 1600), 1), (1, (440, 12, 48), (440, 1440), 1), (3, 440, 880), (1, (880, 16, 64), (880, 3200), 1), (1, (880, 12, 64), (880, 3200), 1), (1, (880, 16, 64), (880, 2880), 1), (1, (880, 12, 64), (880, 2240), 1), (1, (880, 14, 64), (880, 2560), 1), (2, 880, 1000)).

Then, use the searched network_def for searched network training.

3. Searched Network Training

Before running each script, modify IMAGENET_PATH.

For ViT-ResNAS-Tiny, run:

    sh scripts/vit-sr-nas/searched_net/tiny.sh

For ViT-ResNAS-Small, run:

    sh scripts/vit-sr-nas/searched_net/small_mac@2.9G.sh

For ViT-ResNAS-Medium, run:

    sh scripts/vit-sr-nas/searched_net/medium_mac@4.6G.sh

4. Fine-tuning Trained Networks at Higher Resolution

Before running, modify IMAGENET_PATH and FINETUNE_PATH (directed to trained ViT-ResNAS-Medium checkpoint). Then, run:

    sh scripts/vit-sr-nas/finetune/medium_img-size@392.sh

To fine-tune at different resolutions, modify --model, --input-size and --mix-patch-len. We provide models at resolutions 280, 336, and 392 as shown in here. Note that --input-size must be equal to "56 * --mix-patch-len" since the spatial size in ViT-ResNAS is reduced by 56X.

Evaluation

Before running, modify IMAGENET_PATH and MODEL_PATH. Then, run:

    sh scripts/vit-sr-nas/eval/small_mac@2.9G.sh

Questions

Please direct questions to Yi-Lun Liao (ylliao@mit.edu).

License

This repository is released under the CC-BY-NC 4.0. license as found in the LICENSE file.