Discovering Low-Precision Networks Close to Full-Precision Networks for Efficient Inference
To realize the promise of ubiquitous embedded deep network inference, it is essential to seek limits of energy and area efficiency. Low-precision networks offer promise as energy and area scale down quadratically with precision. We demonstrate 8- A nd 4-bit networks that meet or exceed the accuracy of their full-precision versions on the ImageNet classification benchmark. We hypothesize that gradient noise due to quantization during training increases with reduced precision, and seek ways to overcome this. The number of iterations required by SGD to achieve a given training error is related to the square of (a) the distance of the initial solution from the final and (b) the maximum variance of the gradient estimates. Accordingly, we reduce solution distance by starting with pretrained fp32 baseline networks, and combat noise introduced by quantizing weights and activations during training by training longer and reducing learning rates. Sensitivity analysis indicates that these techniques, coupled with activation function range calibration, are sufficient to discover low-precision networks close to fp32 precision baseline networks. Our results provide evidence that 4-bits suffice for classification.