DPACS: Hardware Accelerated Dynamic Neural Network Pruning through Algorithm-Architecture Co-design.

By eliminating compute operations intelligently based on the run time input, dynamic pruning (DP) promises to improve deep neural network inference speed substantially without incurring a major impact on their accuracy. Although many DP algorithms with good pruning performance have been proposed, it remains a challenge to translate these theoretical reductions in compute operations into satisfactory end-to-end speedups in practical real-world implementations. The overhead of identifying operations to be pruned during run time, the need to efficiently process the resulting dynamic dataflow, and the non-trivial memory I/O bottleneck that emerges as the number of compute operations reduces, have all contributed to the challenge of implementing practical DP systems. In this paper, the design and implementation of DPACS are presented to address these challenges. DPACS utilizes a hardware-aware dynamic spatial and channel pruning algorithm in conjunction with a dynamic dataflow engine in hardware to facilitate efficient processing of the pruned network. A channel mask precomputation scheme is designed to reduce memory I/O, and a dedicated inter-layer pipeline is used to achieve efficient indexing and dataflow of sparse activation. Extensive design space exploration has been performed using two architectural variations implemented on FPGA to accelerate multiple networks from the ResNet family on the ImageNet and CIFAR10 dataset across a wide range of pruning ratios. Across the spectrum of configurations, DPACS is able to achieve 1.1× to 3.9× end-to-end speedup over a baseline hardware implementation without pruning. Analysis of the tradeoff among accuracy, compute, and memory I/O performance highlights the importance of algorithm-architecture codesign in developing DP systems.