CPU-GPU Layer-Switched Low Latency CNN Inference

Convolutional Neural Networks (CNNs) inference on Heterogeneous Multi-Processor System-on-Chips (HMPSoCs) in edge devices represent cutting-edge embedded machine learning. Embedded CPU and GPU within an HMPSoC can both perform inference using CNNs. However, common practice is to run a CNN on the HMPSoC component (CPU or GPU) provides the best performance (lowest latency) for that CNN. CNNs are not monolithic and are composed of several layers of different types. Some of these layers have lower latency on the CPU, while others execute faster on the GPU. In this work, we investigate the reason behind this observation. We also propose an execution of CNN that switches between CPU and GPU at the layer granularity, wherein a CNN layer executes on the component that provides it with the lowest latency. Switching between the CPU and the GPU back and forth mid-inference introduces additional overhead (delay) in the inference. Regardless of overhead, we show in this work that a CPU-GPU layer switched execution results in, on average, having 4.72% lower CNN inference latency on the Khadas VIM 3 board with Amlogic A311D HMPSoC.