Title: Quantizing deep convolutional networks for efficient inference: A whitepaper,
Abstract: We present an overview of techniques for quantizing convolutional neural
networks for inference with integer weights and activations. Per-channel
quantization of weights and per-layer quantization of activations to 8-bits of
precision post-training produces classification accuracies within 2% of
floating point networks for a wide variety of CNN architectures. Model sizes
can be reduced by a factor of 4 by quantizing weights to 8-bits, even when
8-bit arithmetic is not supported. This can be achieved with simple, post
training quantization of weights.We benchmark latencies of quantized networks
on CPUs and DSPs and observe a speedup of 2x-3x for quantized implementations
compared to floating point on CPUs. Speedups of up to 10x are observed on
specialized processors with fixed point SIMD capabilities, like the Qualcomm
QDSPs with HVX.
Quantization-aware training can provide further improvements, reducing the
gap to floating point to 1% at 8-bit precision. Quantization-aware training
also allows for reducing the precision of weights to four bits with accuracy
losses ranging from 2% to 10%, with higher accuracy drop for smaller
networks.We introduce tools in TensorFlow and TensorFlowLite for quantizing
convolutional networks and review best practices for quantization-aware
training to obtain high accuracy with quantized weights and activations. We
recommend that per-channel quantization of weights and per-layer quantization
of activations be the preferred quantization scheme for hardware acceleration
and kernel optimization. We also propose that future processors and hardware
accelerators for optimized inference support precisions of 4, 8 and 16 bits.