ProxylessNAS: Direct Neural Architecture Search on Target Task and Hardware
Paper · 2018 · Han Cai, Ligeng Zhu and Song Han
Summary
Neural architecture search typically costs thousands of GPU hours. Differentiable variants such as DARTS and One-Shot are cheaper, but they keep the activations of every candidate operation in memory, so memory grows with the number of choices. As a result, earlier methods search on cheaper stand-ins, such as smaller datasets, shallow networks or short training, and then transfer one repeated cell. That cell may not suit the real task or device. ProxylessNAS treats search as pruning paths inside an over-parameterized network. Each edge holds all candidate operations, but the architecture parameters are binarized so that only one path is active at a time. These gates are trained with a BinaryConnect-style gradient. Hardware cost is made learnable by expressing latency as a differentiable regularization term, with a REINFORCE variant as an alternative. Search runs directly on ImageNet and CIFAR-10 at roughly the cost of normal training, and every block is learned individually. The resulting models outperform strong manual and searched baselines in both accuracy and latency. They also show that different hardware favors differently shaped networks.
Key points
- On CIFAR-10, the found model reaches 2.08% test error with 5.7M parameters. This beats AmoebaNet-B while using about 6× fewer parameters.
- On ImageNet, the model hits 75.1% top-1 accuracy. That is 3.1% above MobileNetV2, and the model runs 1.2× faster in measured GPU latency.
- The mobile ImageNet search took about 200 GPU hours, which the authors estimate is 200× less than MnasNet (around 40,000 V100 GPU hours). The resulting model matches MobileNetV2 1.4 accuracy while running 1.8× faster.
- Path binarization cuts memory use by about an order of magnitude. The CIFAR-10 search space has 7 candidate operations: several depthwise-separable convolutions, a dilated depthwise-separable convolution, identity, and average and max pooling.
- The mobile latency predictor was built from 5k sampled architectures (4k for fitting, the rest for testing) measured on a Google Pixel 1 with TensorFlow-Lite. It has an RMSE of 0.75 ms.
- Pretrained models and evaluation code are available at github.com/MIT-HAN-LAB/ProxylessNAS.
Interesting ideas
- I1. Search as pruning. Instead of training a separate controller, the method trains one oversized network and lets learned gates decide which branches survive. This links architecture choice to model compression and could be reused wherever we want to choose among module variants, such as layers in a text model.
- I2. Sample one path per step. Activating a single sampled branch, rather than mixing all of them, keeps memory near that of a compact model. This makes searching large option sets feasible on ordinary GPUs and full-size data, without falling back to toy proxies.
- I3. Recompute inactive branches in backward. Outputs of unused paths are needed only to compute gate gradients. They can be computed during the backward pass and freed immediately, which saves memory without approximation. The same trick applies to any gated mixture where some branches are idle in the forward pass.
- I4. Cheap latency model as a differentiable penalty. A small regressor fitted on measurements from one device can replace a farm of phones. Folding its prediction into the loss lets deployment cost be optimized jointly with accuracy, which is relevant for shipping NLP models to CPUs or mobile devices.
- I5. Search with estimates, report measurements. The predicted latency guides the search, but final numbers come from real on-device runs. This is a good evaluation habit whenever a surrogate metric drives optimization.
Institutions
Fields, topics and concepts
📚 Shelves 3The field of science this work belongs to (OpenAlex fields).Computer Science · 18,614 worksArtificial Intelligence · 17,965 worksComputer Vision and Pattern Recognition · 3,486 works
🧭 Topics 1Research subjects and languages the work is about.GPU & parallel computing · 41 works
Cite
Cite as Han Cai, Ligeng Zhu and Song Han. 2018. ProxylessNAS: Direct Neural Architecture Search on Target Task and Hardware. arXiv:1812.00332.
@misc{cai2018proxylessnas,
title = {{ProxylessNAS: Direct Neural Architecture Search on Target Task and Hardware}},
author = {Han Cai, Ligeng Zhu and Song Han},
year = {2018},
doi = {10.48550/arxiv.1812.00332},
eprint = {1812.00332},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.1812.00332}
}References
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