Practical Network Acceleration With Tiny Sets: Hypothesis, Theory, and Algorithm

Due to data privacy issues, accelerating networks with tiny training sets has become a critical need in practice. Previous methods achieved promising results empirically by filter-level pruning. In this paper, we both study this problem theoretically and propose an effective algorithm aligning well with our theoretical results. First, we propose the finetune convexity hypothesis to explain why recent few-shot compression algorithms do not suffer from overfitting problems. Based on it, a theory is further established to explain these methods for the first time. Compared to naively finetuning a pruned network, feature mimicking is proved to achieve a lower variance of parameters and hence enjoys easier optimization. With our theoretical conclusions, we claim dropping blocks is a fundamentally superior few-shot compression scheme in terms of more convex optimization and a higher acceleration ratio. To choose which blocks to drop, we propose a new metric, recoverability, to effectively measure the difficulty of recovering the compressed network. Finally, we propose an algorithm named Practise to accelerate networks using only tiny sets of training images. Practise outperforms previous methods by a significant margin. For 22% latency reduction, Practise surpasses previous methods by on average 7 percentage points on ImageNet-1k. It also enjoys high generalization ability, working well under data-free or out-of-domain data settings, too.