  We present APQ for efficient deep learning inference on resource-constrained
hardware. Unlike previous methods that separately search the neural
architecture, pruning policy, and quantization policy, we optimize them in a
joint manner. To deal with the larger design space it brings, a promising
approach is to train a quantization-aware accuracy predictor to quickly get the
accuracy of the quantized model and feed it to the search engine to select the
best fit. However, training this quantization-aware accuracy predictor requires
collecting a large number of quantized <model, accuracy> pairs, which involves
quantization-aware finetuning and thus is highly time-consuming. To tackle this
challenge, we propose to transfer the knowledge from a full-precision (i.e.,
fp32) accuracy predictor to the quantization-aware (i.e., int8) accuracy
predictor, which greatly improves the sample efficiency. Besides, collecting
the dataset for the fp32 accuracy predictor only requires to evaluate neural
networks without any training cost by sampling from a pretrained once-for-all
network, which is highly efficient. Extensive experiments on ImageNet
demonstrate the benefits of our joint optimization approach. With the same
accuracy, APQ reduces the latency/energy by 2x/1.3x over MobileNetV2+HAQ.
Compared to the separate optimization approach (ProxylessNAS+AMC+HAQ), APQ
achieves 2.3% higher ImageNet accuracy while reducing orders of magnitude GPU
hours and CO2 emission, pushing the frontier for green AI that is
environmental-friendly. The code and video are publicly available.
