SPEED: A Scalable RISC-V Vector Processor Enabling Efficient Multi-Precision DNN Inference

Abstract

Deploying deep neural networks (DNNs) on those resource-constrained edge platforms is hindered by their substantial computation and storage demands. Quantized multi-precision DNNs, denoted as MP-DNNs, offer a promising solution for these limitations but pose challenges for existing RISC-V processors due to complex instructions, suboptimal parallel processing, and inefficient dataflow mapping. To tackle the challenges mentioned above, SPEED, a scalable RISC-V vector (RVV) processor, is proposed to enable efficient MP-DNN inference, incorporating innovations in customized instructions, hardware architecture, and dataflow mapping. Firstly, some dedicated customized RISC-V instructions are introduced based on RVV extensions to reduce the instruction complexity, allowing SPEED to support processing precision ranging from 4-bit to 16-bit with minimized hardware overhead. Secondly, a parameterized multi-precision tensor unit is developed and integrated within the scalable module to enhance parallel processing capability by providing reconfigurable parallelism that matches the computation patterns of diverse MP-DNNs. Finally, a flexible mixed dataflow method is adopted to improve computational and energy efficiency according to the computing patterns of different DNN operators. The synthesis of SPEED is conducted on TSMC 28nm technology. Experimental results show that SPEED achieves a peak throughput of 737.9 GOPS and an energy efficiency of 1383.4 GOPS/W for 4-bit operators. Furthermore, SPEED exhibits superior area efficiency compared to prior RVV processors, with enhancements of 5.9$\sim$26.9$\times$ and 8.2$\sim$18.5$\times$ for 8-bit operator and best integer performance, respectively, which highlights SPEED's significant potential for efficient MP-DNN inference.