UPSCALE: Unconstrained Channel Pruning
Alvin Wan Hanxiang Hao Kaushik Patnaik Yueyang Xu Omer Hadad David Güera Zhile Ren Qi Shan
As neural networks grow in size and complexity, inference speeds decline. To
combat this, one of the most effective compression techniques -- channel
pruning -- removes channels from weights. However, for multi-branch segments of
a model, channel removal can introduce inference-time memory copies. In turn,
these copies increase inference latency -- so much so that the pruned model can
be slower than the unpruned model. As a workaround, pruners conventionally
constrain certain channels to be pruned together. This fully eliminates memory
copies but, as we show, significantly impairs accuracy. We now have a dilemma:
Remove constraints but increase latency, or add constraints and impair
accuracy. In response, our insight is to reorder channels at export time, (1)
reducing latency by reducing memory copies and (2) improving accuracy by
removing constraints. Using this insight, we design a generic algorithm UPSCALE
to prune models with any pruning pattern. By removing constraints from existing
pruners, we improve ImageNet accuracy for post-training pruned models by 2.1
points on average -- benefiting DenseNet (+16.9), EfficientNetV2 (+7.9), and
ResNet (+6.2). Furthermore, by reordering channels, UPSCALE improves inference
speeds by up to 2x over a baseline export.