Atalanta is a lossless, hardware/software co-designed compression technique for the tensors of fixed-point quantized deep neural networks. Atalanta increases effective memory capacity, reduces off-die traffic, and/or helps to achieve the desired performance/energy targets while using smaller off-die memories during inference. Atalanta is architected to deliver nearly identical coding efficiency compared to Arithmetic Coding while avoiding its complexity, overhead, and bandwidth limitations. Indicatively, the Atalanta decoder and encoder units each use less than 50B of internal storage. In hardware, Atalanta is implemented as an assist over any machine learning accelerator transparently compressing/decompressing tensors just before the off-die memory controller. This work shows the performance and energy efficiency of Atalanta when implemented in a 65nm technology node. Atalanta reduces data footprint of weights and activations to 60% and 48% respectively on average over a wide set of 8-bit quantized models and complements a wide range of quantization methods. Integrated with a Tensorcore-based accelerator, Atalanta boosts the speedup and energy efficiency to 1.44× and 1.37×, respectively. Atalanta is effective at compressing the stashed activations during training for fixed-point inference.

BitPruning is a training method for minimizing inference bitlengths at any granularity while maintaining accuracy. BitPruning extends the meaning of fixed-point bitlenghts into the continuous domain by interpolating between the nearest two integers, enabling gradient descent to learn bitlengths together with other parameters. A novel regularizer penalizes large bitlength representations and can be modified to minimize other quantifiable criteria, such as number of operations or memory footprint. BitPruning learns thrifty representations while maintaining accuracy: With ImageNet, it produces an average per layer bitlength of 3.76 and 4.36 bits on ResNet18 and MobileNet V2 respectively, remaining within 0.5% of the base TOP-1 accuracy. Simple modifications of the BitPruning regularizer can be used to further reduce compute workload by up to 24%, as well as memory footprint in activation or weight-heavy tasks by up to 14% and 8% respectively.

Data accesses between on- and off-chip memories account for a large fraction of overall energy consumption during inference with deep learning networks. We present Boveda, a lossless on-chip memory compression technique for neural networks operating on fixed-point values. Boveda reduces the datawidth used per block of values to be only as long as necessary: since most values are of small magnitude Boveda drastically reduces their footprint. Boveda can be used to increase the effective on-chip capacity, to reduce off-chip traffic, or to reduce the on-chip memory capacity needed to achieve a performance/energy target. Boveda reduces total model footprint to 53%.

Weight and activation sparsity can be leveraged in hardware to boost the performance and energy efficiency of Deep Neural Networks during inference. Fully capitalizing on sparsity requires re-scheduling and mapping the execution stream to deliver non-zero weight/activation pairs to multiplier units for maximal utilization and reuse. However, permitting arbitrary value re-scheduling in memory space and in time places a considerable burden on hardware to perform dynamic at-runtime routing and matching of values, and incurs significant energy inefficiencies. Bit-Tactical (TCL) is a neural network accelerator where the responsibility for exploiting weight sparsity is shared between a novel static scheduling middleware, and a co-designed hardware front-end with a lightweight sparse shuffling network comprising two (2- to 8-input) multiplexers per activation input. We empirically motivate two back-end designs chosen to target bit-sparsity in activations, rather than value-sparsity, with two benefits: a) we avoid handling the dynamically sparse whole-value activation stream, and b) we uncover more ineffectual work. TCL outperforms other state-of-the-art accelerators that target sparsity for weights and activations, the dynamic precision requirements of activations, or their bit-level sparsity for a variety of neural networks.

We present a method for transparently identifying ineffectual computations during inference with Deep Learning models. Specifically, by decomposing multiplications down to the bit level, the amount of work needed by multiplications during inference can be potentially reduced by at least 40× across a wide selection of neural networks (8b and 16b). This method produces numerically identical results and does not affect overall accuracy. We present Laconic, a hardware accelerator that implements this approach to boost energy efficiency for inference with Deep Learning Networks. Laconic judiciously gives up some of the work reduction potential to yield a low-cost, simple, and energy efficient design that outperforms other state-of-the-art accelerators: an optimized DaDianNao-like design [13], Eyeriss [15], SCNN [71], Pragmatic [3], and BitFusion [83]. We study 16b, 8b, and 1b/2b fixed-point quantized models.

Hardware accelerators for inference with neural networks can take advantage of the properties of data they process. Performance gains and reduced memory bandwidth during inference have been demonstrated by using narrower data types [1] [2] and by exploiting the ability to skip and compress values that are zero [3]-[6]. Similarly useful properties have been identified at a lower-level such as varying precision requirements [7] and bit-level sparsity [8] [9]. To date, the analysis of these potential sources of superfluous computation and communication has been constrained to a small number of older Convolutional Neural Networks (CNNs) used for image classification. It is an open question as to whether they exist more broadly. This paper aims to determine whether these properties persist in: (1) more recent and thus more accurate and better performing image classification networks, (2) models for image applications other than classification such as image segmentation and low-level computational imaging, (3) Long-Short-Term-Memory (LSTM) models for non-image applications such as those for natural language processing, and (4) quantized image classification models. We demonstrate that such properties persist and discuss the implications and opportunities for future accelerator designs.

We show that selecting a data width for all values in Deep Neural Networks, quantized or not and even if that width is different per layer, amounts to worst-case design. Much shorter data widths can be used if we target the common case by adjusting the data type width at a much finer granularity. We propose ShapeShifter, where we group weights and activations and encode them using a width specific to each group and where typical group sizes vary from 16 to 256 values. The per group widths are selected statically for the weights and dynamically by hardware for the activations. We present two applications of ShapeShifter. In the first, that is applicable to any system, ShapeShifter reduces off- and on-chip storage and communication. This ShapeShifter-based memory compression is simple and low cost yet reduces off-chip traffic to 33% and 36% for 8-bit and 16-bit models respectively. This makes it possible to sustain higher performance for a given off-chip memory interface while also boosting energy efficiency. In the second application, we show how ShapeShifter can be implemented as a surgical extension over designs that exploit variable precision in time.