DeepFlexiHLS: Deep Neural Network Flexible High-Level Synthesis Directive Generator
Mohammad Riazati, Masoud Daneshtalab, Mikael Sjödin, Björn Lisper · 2022
Deep Neural Networks (DNNs) are now widely adopted to solve various problems ranging from speech recognition to image classification. Since DNNs demand a large amount of processing power, their implementation on hardware, i.e., FPGA or ASIC, has received much attention. High-level synthesis is widely used since it significantly boosts productivity and flexibility and requires minimal hardware knowledge. However, when HLS transforms a C implementation to a Register-Transfer Level one, the high parallelism capability of the FPGA is not well-utilized. HLS tools provide a feature called directives through which designers can guide the tool using some defined C pragma statements to improve performance. Nevertheless, finding appropriate directives is another challenge, which needs considerable expertise and experience. This paper proposes DeepFlexiHLS, a two-stage design space exploration flow to find a set of directives to achieve minimal latency. In the first stage, a partition-based method is used to find the directives corresponding to each partition. Aggregating all these directives leads to minimal latency. Experimental results show 54% more speed-up than similar work on VGG neural network. In the second stage, an estimator is implemented to find the latency and resource utilization of various combinations of the found directives. The results form a Pareto-frontier from which the designer can choose if FPGA resources are limited or are not to be entirely used by the DNN module.