Abstract

The current trend for deep learning has come with an enormous computational need for billions of Multiply-Accumulate (MAC) operations per inference. Fortunately, reduced precision has demonstrated large benefits with low impact on accuracy, paving the way towards processing in mobile devices and IoT nodes. To this end, various precision-scalable MAC architectures optimized for neural networks have recently been proposed. Yet, it has been hard to comprehend their differences and make a fair judgment of their relative benefits as they have been implemented with different technologies and performance targets. To overcome this, this work exhaustively reviews the state-of-the-art precision-scalable MAC architectures and unifies them in a new taxonomy. Subsequently, these different topologies are thoroughly benchmarked in a 28nm commercial CMOS process, across a wide range of performance targets, and with precision ranging from 2 to 8 bits. Circuits are analyzed for each precision as well as jointly in practical use cases, highlighting the impact of architectures and scalability in terms of energy, throughput, area and bandwidth, aiming to understand the key trends to reduce computation costs in neural-network processing.

Highlights

  • E MBEDDED deep learning has gained a lot of attention nowadays due to its broad application prospects and vast potential market

  • Since the various MAC architectures should have very different optimal operating frequencies, this study explores a broad range of clock targets with frequencies from 600 MHz to 4 GHz

  • This study models the impact of Dynamic Voltage-Frequency Scaling (DVFS) on the circuits, assessing throughput and energy for each mode while sweeping the voltage from 1 V down to 0.8 V

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Summary

INTRODUCTION

E MBEDDED deep learning has gained a lot of attention nowadays due to its broad application prospects and vast potential market. The main challenge to embrace this era of edge intelligence comes from the supply-anddemand gap between the limited energy budget of embedded devices, often battery powered, and the computationallyintensive deep-learning algorithms, requiring billions of Multiply-Accumulate (MAC) operations and data movements To alleviate this unbalanced relationship, many approaches have been investigated at different levels of abstraction. New topologies have been proposed at circuit level to improve energy or performance beyond conventional design by exploiting data locality or error tolerance [6]–[8] Among these techniques, reduced-precision computing has demonstrated large benefits with low or negligible impact on the network accuracy [9], [10]. Source code and supplementary materials are available online at: https://github.com/vincent-camus/benchmarkingprecision-scalable-mac-units

DATAFLOW IMPLICATIONS OF PRECISION SCALABILITY
SA and ST at Algorithm Level
SA and ST at Precision-Scalable MAC-Unit Level
SA and ST at PE-Array Level
Taxonomy
SURVEY OF SCALABLE MAC ARCHITECTURES
DESIGN AND BENCHMARK METHODOLOGY
Design Considerations and Assumptions
Design Space
DETAILED ANALYSIS
Physical Implementation and Timing Analysis
Power Estimation
Bandwidth
Bandwidth per Operation
Throughput Evaluation
Area Breakdown
Energy Overhead at Full Precision
Energy Scaling
Comparison of Scalable MACs at Nominal Voltage
Comparison of Scalable MACs with DVFS
Introduction and Methodology
Equal Usage
Findings
VIII. CONCLUSION
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