Publications

Forthcoming
S. Krishnan, B. Boroujerdian, W. Fu, A. Faust, and V. J. Reddi, “Air Learning: An AI Research Platform for Algorithm-Hardware Benchmarking of Autonomous Aerial Robots,” Springer Machine Learning Journal, no. Special Issue on Reinforcement Learning for Real Life, Forthcoming. arXiv VersionAbstract
We introduce Air Learning, an AI research platform for benchmarking algorithm-hardware performance and energy efficiency trade-offs. We focus in particular on deep reinforcement learning (RL) interactions in autonomous unmanned aerial vehicles (UAVs). Equipped with a random environment generator, AirLearning exposes a UAV to a diverse set of challenging scenarios. Users can specify a task, train different RL policies and evaluate their performance and energy efficiency on a variety of hardware platforms. To show how Air Learning can be used, we seed it with Deep Q Networks (DQN) and Proximal Policy Optimization (PPO) to solve a point-to-point obstacle avoidance task in three different environments, generated using our configurable environment generator. We train the two algorithms using curriculum learning and non-curriculum-learning. Air Learning assesses the trained policies' performance, under a variety of quality-of-flight (QoF) metrics, such as the energy consumed, endurance and the average trajectory length, on resource-constrained embedded platforms like a Ras-Pi. We find that the trajectories on an embedded Ras-Pi are vastly different from those predicted on a high-end desktop system, resulting in up to 79.43% longer trajectories in one of the environments. To understand the source of such differences, we use Air Learning to artificially degrade desktop performance to mimic what happens on a low-end embedded system. QoF metrics with hardware-in-the-loop characterize those differences and expose how the choice of onboard compute affects the aerial robot's performance. We also conduct reliability studies to demonstrate how Air Learning can help understand how sensor failures affect the learned policies. All put together, Air Learning enables a broad class of RL studies on UAVs. More information and code for Air Learning can be found here.
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2021
B. Plancher, S. M. Neuman, T. Bourgeat, S. Kuindersma, S. Devadas, and V. J. Reddi, “Accelerating Robot Dynamics Gradients on a CPU, GPU, and FPGA,” IEEE Robotics and Automation Letters, vol. 6, no. 2, pp. 2335-2342, 2021. IEEE VersionAbstract
Computing the gradient of rigid body dynamics is a central operation in many state-of-the-art planning and control algorithms in robotics. Parallel computing platforms such as GPUs and FPGAs can offer performance gains for algorithms with hardware-compatible computational structures. In this letter, we detail the designs of three faster than state-of-the-art implementations of the gradient of rigid body dynamics on a CPU, GPU, and FPGA. Our optimized FPGA and GPU implementations provide as much as a 3.0x end-to-end speedup over our optimized CPU implementation by refactoring the algorithm to exploit its computational features, e.g., parallelism at different granularities. We also find that the relative performance across hardware platforms depends on the number of parallel gradient evaluations required.
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M. Lam, et al., “ActorQ: Quantization for Actor-Learner Distributed Reinforcement Learning,” in ICLR, Hardware Aware Efficient Training Workshop at ICLR 2021, Virtual, May 7, 2021.Abstract
In this paper, we introduce a novel Reinforcement Learning (RL) training paradigm, ActorQ, for speeding up actor-learner distributed RL training. ActorQ leverages full precision optimization on the learner, and distributed data collection through lower-precision quantized actors. The quantized, 8-bit (or 16 bit) inference on actors, speeds up data collection without affecting the convergence. The quantized distributed RL training system, ActorQ, demonstrates end to end speedups of > 1.5 × - 2.5 ×, and faster convergence over full precision training on a range of tasks (Deepmind Control Suite) and different RL algorithms (D4PG, DQN). Finally, we break down the various runtime costs of distributed RL training (such as communication time, inference time, model load time, etc) and evaluate the effects of quantization on these system attributes.
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M. Buch, Z. Azad, A. Joshi, and V. J. Reddi, “AI Tax in Mobile SoCs: End-to-end Performance Analysis of Machine Learning in Smartphones,” in 2021 IEEE International Symposium on Performance Analysis of Systems and Software, ISPASS '21, Virtual, Stony Brook, NY, March 28-30, 2021. IEEE VersionAbstract
Mobile software is becoming increasingly feature rich, commonly being accessorized with the powerful decision making capabilities of machine learning (ML). To keep up with the consequently higher power and performance demands, system and hardware architects add specialized hardware units onto their system-on-chips (SoCs) coupled with frameworks to delegate compute optimally. While these SoC innovations are rapidly improving ML model performance and power efficiency, auxiliary data processing and supporting infrastructure to enable ML model execution can substantially alter the performance profile of a system. This work posits the existence of an AI tax, the time spent on non-model execution tasks. We characterize the execution pipeline of open source ML benchmarks and Android applications in terms of AI tax and discuss where performance bottlenecks may unexpectedly arise.
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D. Richins, et al., “AI Tax: The Hidden Cost of AI Data Center Applications,” ACM Transactions on Computer Systems (TOCS), vol. 37, no. 1-4, pp. 1-32, 2021. ACM Digital Library VersionAbstract
Artificial intelligence and machine learning are experiencing widespread adoption in industry and academia. This has been driven by rapid advances in the applications and accuracy of AI through increasingly complex algorithms and models; this, in turn, has spurred research into specialized hardware AI accelerators. Given the rapid pace of advances, it is easy to forget that they are often developed and evaluated in a vacuum without considering the full application environment. This article emphasizes the need for a holistic, end-to-end analysis of artificial intelligence (AI) workloads and reveals the “AI tax.” We deploy and characterize Face Recognition in an edge data center. The application is an AI-centric edge video analytics application built using popular open source infrastructure and machine learning (ML) tools. Despite using state-of-the-art AI and ML algorithms, the application relies heavily on pre- and post-processing code. As AI-centric applications benefit from the acceleration promised by accelerators, we find they impose stresses on the hardware and software infrastructure: storage and network bandwidth become major bottlenecks with increasing AI acceleration. By specializing for AI applications, we show that a purpose-built edge data center can be designed for the stresses of accelerated AI at 15% lower TCO than one derived from homogeneous servers and infrastructure.
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V. J. Reddi, G. Diamos, P. Warden, P. Mattson, and D. Kanter, “Data Engineering for Everyone,” 2021. arXiv VersionAbstract
Data engineering is one of the fastest-growing fields within machine learning (ML). As ML becomes more common, the appetite for data grows more ravenous. But ML requires more data than individual teams of data engineers can readily produce, which presents a severe challenge to ML deployment at scale. Much like the software-engineering revolution, where mass adoption of open-source software replaced the closed, in-house development model for infrastructure code, there is a growing need to enable rapid development and open contribution to massive machine learning data sets. This article shows that open-source data sets are the rocket fuel for research and innovation at even some of the largest AI organizations. Our analysis of nearly 2000 research publications from Facebook, Google and Microsoft over the past five years shows the widespread use and adoption of open data sets. Open data sets that are easily accessible to the public are vital to accelerate ML innovation for everyone. But such open resources are scarce in the wild. So, can we accelerate data set creation and enable the rapid development of open data sets, akin to the rapid development of open-source software? Moreover, can we develop automatic data set generation frameowrks and tools to avert the data scarcity crisis?
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M. Mazumder, C. Banbury, J. Meyer, P. Warden, and V. J. Reddi, “Few-Shot Keyword Spotting in Any Language,” in INTERSPEECH 2021, Virtual, Brno, Czech Republic, 2021. arXiv VersionAbstract
We introduce a few-shot transfer learning method for keyword spotting in any language. Leveraging open speech corpora in nine languages, we automate the extraction of a large multilingual keyword bank and use it to train an embedding model. With just five training examples, we fine-tune the embedding model for keyword spotting and achieve an average F1 score of 0.75 on keyword classification for 180 new keywords unseen by the embedding model in these nine languages. This embedding model also generalizes to new languages. We achieve an average F1 score of 0.65 on 5-shot models for 260 keywords sampled across 13 new languages unseen by the embedding model. We investigate streaming accuracy for our 5-shot models in two contexts: keyword spotting and keyword search. Across 440 keywords in 22 languages, we achieve an average streaming keyword spotting accuracy of 85.2% with a false acceptance rate of 1.2%, and observe promising initial results on keyword search.
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E. Shaotran, J. J. Cruz, and V. J. Reddi, “GLADAS: Gesture Learning for Advanced Driver Assistance Systems,” in IEEE International Conference on Autonomous Systems, ICAS 2021, Montréal, Québec, Canada, August 11-13, 2021, 2021. arXiv VersionAbstract
Human-computer interaction (HCI) is crucial for safety as autonomous vehicles (AVs) become commonplace. Yet, little effort has been put toward ensuring that AVs understand human communications on the road. In this paper, we present Gesture Learning for Advanced Driver Assistance Systems (GLADAS), a deep learning-based self-driving car hand gesture recognition system developed and evaluated using virtual simulation. We focus on gestures as they are a natural and common way for pedestrians to interact with drivers. We challenge the system to perform in typical, everyday driving interactions with humans. Our results provide a baseline performance of 94.56% accuracy and 85.91% F1 score, promising statistics that surpass human performance and motivate the need for further research into human-AV interaction.
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B. P. Duisterhof, et al., “Learning to Seek: Autonomous Source Seeking with Deep Reinforcement Learning Onboard a Nano Drone Microcontroller,” 2021. arXiv VersionAbstract
Fully autonomous navigation using nano drones has numerous applications in the real world, ranging from search and rescue to source seeking. Nano drones are wellsuited for source seeking because of their agility, low price, and ubiquitous character. Unfortunately, their constrained form factor limits flight time, sensor payload, and compute capability. These challenges are a crucial limitation for the use of source-seeking nano drones in GPS-denied and highly cluttered environments. Hereby, we introduce a fully autonomous deep reinforcement learning-based light-seeking nano drone. The 33-gram nano drone performs all computation on-board the ultra-low-power microcontroller (MCU). We present the method for efficiently training, converting, and utilizing deep reinforcement learning policies. Our training methodology and novel quantization scheme allow fitting the trained policy in 3 kB of memory. The quantization scheme uses representative input data and input scaling to arrive at a full 8-bit model. Finally, we evaluate the approach in simulation and flight tests using a Bitcraze CrazyFlie, achieving 80% success rate on average in a highly cluttered and randomized test environment. Even more, the drone finds the light source in 29% fewer steps compared to a baseline simulation (obstacle avoidance without source information). To our knowledge, this is the first deep reinforcement learning method that enables source seeking within a highly constrained nano drone demonstrating robust flight behavior. Our general methodology is suitable for any (source seeking) highly constrained platform using deep reinforcement learning. Code & video: https://github. com/harvard-edge/source-seeking
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S. M. Neuman, B. Plancher, T. Bourgeat, T. Tambe, S. Devadas, and V. J. Reddi, “Robomorphic computing: a design methodology for domain-specific accelerators parameterized by robot morphology,” Proceedings of the 26th ACM International Conference on Architectural Support for Programming Languages and Operating Systems. ACM, pp. 674-686, 2021.Abstract
Robotics applications have hard time constraints and heavy computational burdens that can greatly benefit from domain-specific hardware accelerators. For the latency-critical problem of robot motion planning and control, there exists a performance gap of at least an order of magnitude between joint actuator response rates and state-of-the-art software solutions. Hardware acceleration can close this gap, but it is essential to define automated hardware design flows to keep the design process agile as applications and robot platforms evolve. To address this challenge, we introduce robomorphic computing: a methodology to transform robot morphology into a customized hardware accelerator morphology. We (i) present this design methodology, using robot topology and structure to exploit parallelism and matrix sparsity patterns in accelerator hardware; (ii) use the methodology to generate a parameterized accelerator design for the gradient of rigid body dynamics, a key kernel in motion planning; (iii) evaluate FPGA and synthesized ASIC implementations of this accelerator for an industrial manipulator robot; and (iv) describe how the design can be automatically customized for other robot models. Our FPGA accelerator achieves speedups of 8× and 86× over CPU and GPU when executing a single dynamics gradient computation. It maintains speedups of 1.9× to 2.9× over CPU and GPU, including computation and I/O round-trip latency, when deployed as a coprocessor to a host CPU for processing multiple dynamics gradient computations. ASIC synthesis indicates an additional 7.2× speedup for single computation latency. We describe how this principled approach generalizes to more complex robot platforms, such as quadrupeds and humanoids, as well as to other computational kernels in robotics, outlining a path forward for future robomorphic computing accelerators.
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B. P. Duisterhof, S. Li, J. Burgués, V. J. Reddi, and G. C. H. E. de Croon, “Sniffy Bug: A Fully Autonomous Swarm of Gas-Seeking Nano Quadcopters in Cluttered Environments,” in International Conference on Intelligent Robots and Systems, IROS 2021, Prague, Czech Republic (Virtual), 2021. arXiv VersionAbstract

Nano quadcopters are ideal for gas source localization (GSL) as they are safe, agile and inexpensive. However, their extremely restricted sensors and computational resources make GSL a daunting challenge. We propose a novel bug algorithm named ‘Sniffy Bug’, which allows a fully autonomous swarm of gas-seeking nano quadcopters to localize a gas source in unknown, cluttered, and GPS-denied environments. The computationally efficient, mapless algorithm foresees in the avoidance of obstacles and other swarm members, while pursuing desired waypoints. The waypoints are first set for exploration, and, when a single swarm member has sensed the gas, by a particle swarm optimization-based (PSO) procedure. We evolve all the parameters of the bug (and PSO) algorithm using our novel simulation pipeline, ‘AutoGDM’. It builds on and expands open source tools in order to enable fully automated end-to-end environment generation and gas dispersion modeling, allowing for learning in simulation. Flight tests show that Sniffy Bug with evolved parameters outperforms manually selected parameters in cluttered, real-world environments. Videos: https://bit.ly/37MmtdL

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2020
T. Tambe, et al., “AdaptivFloat: A Floating-point based Data Type for Resilient Deep Learning Inference,” arXiv preprint arXiv:1909.13271, 2020. arXiv VersionAbstract
Conventional hardware-friendly quantization methods, such as fixed-point or integer, tend to perform poorly at very low word sizes as their shrinking dynamic ranges cannot adequately capture the wide data distributions commonly seen in sequence transduction models. We present AdaptivFloat, a floating-point inspired number representation format for deep learning that dynamically maximizes and optimally clips its available dynamic range, at a layer granularity, in order to create faithful encoding of neural network parameters. AdaptivFloat consistently produces higher inference accuracies compared to block floating-point, uniform, IEEE-like float or posit encodings at very low precision (≤ 8-bit) across a diverse set of state-of-the-art neural network topologies. And notably, AdaptivFloat is seen surpassing baseline FP32 performance by up to +0.3 in BLEU score and -0.75 in word error rate at weight bit widths that are ≤ 8-bit. Experimental results on a deep neural network (DNN) hardware accelerator, exploiting AdaptivFloat logic in its computational datapath, demonstrate per-operation energy and area that is 0.9× and 1.14×, respectively, that of equivalent bit width integer-based accelerator variants.
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T. Tambe, et al., “Algorithm-Hardware Co-Design of Adaptive Floating-Point Encodings for Resilient Deep Learning Inference,” in 2020 57th ACM/IEEE Design Automation Conference, DAC '20, July 20-24, Virtual, San Francisco, CA, 2020, pp. 1-6. IEEE VersionAbstract
Conventional hardware-friendly quantization methods, such as fixed-point or integer, tend to perform poorly at very low precision as their shrunken dynamic ranges cannot adequately capture the wide data distributions commonly seen in sequence transduction models. We present an algorithm-hardware co-design centered around a novel floating-point inspired number format, AdaptivFloat, that dynamically maximizes and optimally clips its available dynamic range, at a layer granularity, in order to create faithful encodings of neural network parameters. AdaptivFloat consistently produces higher inference accuracies compared to block floating-point, uniform, IEEE-like float or posit encodings at low bit precision (≤8-bit) across a diverse set of state-of-the-art neural networks, exhibiting narrow to wide weight distribution. Notably, at 4-bit weight precision, only a 2.1 degradation in BLEU score is observed on the AdaptivFloat-quantized Transformer network compared to total accuracy loss when encoded in the above-mentioned prominent datatypes. Furthermore, experimental results on a deep neural network (DNN) processing element (PE), exploiting AdaptivFloat logic in its computational datapath, demonstrate per-operation energy and area that is 0.9× and 1.14×, width, respectively that of an equivalent bit NVDLA-like integer-based PE.
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J. Leng, et al., “Asymmetric Resilience: Exploiting Task-Level Idempotency for Transient Error Recovery in Accelerator-Based Systems,” in 2020 IEEE International Symposium on High Performance Computer Architecture (HPCA), 2020, pp. 44-57.Abstract
Accelerators make the task of building systems that are re-silient against transient errors like voltage noise and soft errors hard. Architects integrate accelerators into the system as black box third-party IP components. So a fault in one or more accelerators may threaten the system's reliability if there are no established failure semantics for how an error propagates from the accelerator to the main CPU. Existing solutions that assure system reliability come at the cost of sacrificing accelerator generality, efficiency, and incur significant overhead, even in the absence of errors. To over-come these drawbacks, we examine reliability management of accelerator systems via hardware-software co-design, coupling an efficient architecture design with compiler and run-time support, to cope with transient errors. We introduce asymmetric resilience that architects reliability at the system level, centered around a hardened CPU, rather than at the accelerator level. At runtime, the system exploits task-level idempotency to contain accelerator errors and use memory protection instead of taking checkpoints to mitigate over-heads. We also leverage the fact that errors rarely occur in systems, and exploit the trade-off between error recovery performance and improved error-free performance to enhance system efficiency. Using GPUs, which are at the fore-front of accelerator systems, we demonstrate how our system architecture manages reliability in both integrated and discrete systems, under voltage-noise and soft-error related faults, leading to extremely low overhead (less than 1%) and substantial gains (20% energy savings on average).
C. R. Banbury, et al., “Benchmarking TinyML Systems: Challenges and Direction”. 2020.
Z. Azad, et al., “An end-to-end RISC-V solution for ML on the edge using in-pipeline support,” in Boston Area Architecture (BARC) Workshop, 2020. Publisher's VersionAbstract
Machine Learning (ML) is widely used today in many mobile applications. To preserve user privacy, there is a need to perform ML inference on the mobile devices. Given that ML inference is a computationally intensive task, the common technique used in mobile devices is offloading the task to a neural accelerator. However, the speed-up gained from offloading these tasks on the accelerators is limited by the overhead of frequent host-accelerator communication. In this paper, we propose a complete end-to-end solution that uses in-pipeline machine learning processing unit for accelerating ML workloads. First we introduce the software infrastructure we developed to support compilation and execution of machine learning models used in TensorFlow Lite framework. Then we discuss the microarchitecture we plan to implement for supporting the execution of our vectorized machine learning kernels.
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G. Papadimitriou, et al., “Exceeding Conservative Limits: A Consolidated Analysis on Modern Hardware Margins,” IEEE Transactions on Device and Materials Reliability, vol. 20, no. 2, pp. 341-350, 2020.Abstract
Modern large-scale computing systems (data centers, supercomputers, cloud and edge setups and high-end cyber-physical systems) employ heterogeneous architectures that consist of multicore CPUs, general-purpose many-core GPUs, and programmable FPGAs. The effective utilization of these architectures poses several challenges, among which a primary one is power consumption. Voltage reduction is one of the most efficient methods to reduce power consumption of a chip. With the galloping adoption of hardware accelerators (i.e., GPUs and FPGAs) in large datacenters and other large-scale computing infrastructures, a comprehensive evaluation of the safe voltage reduction levels for each different chip can be employed for efficient reduction of the total power. We present a survey of recent studies in voltage margins reduction at the system level for modern CPUs, GPUs and FPGAs. The pessimistic voltage guardbands inserted by the silicon vendors can be exploited in all devices for significant power savings. On average, voltage reduction can reach 12% in multicore CPUs, 20% in manycore GPUs and 39% in FPGAs.
B. P. Duisterhof, et al., “Learning to Seek: Deep Reinforcement Learning for Phototaxis of a Nano Drone in an Obstacle Field”. 2020.
D. Richins, et al., “Missing the Forest for the Trees: End-to-End AI Application Performance in Edge Data Centers,” in International Symposium on High Performance Computer Architecture (HPCA), 2020.Abstract

Artificial intelligence and machine learning are experiencing widespread adoption in the industry, academia, and even public consciousness. This has been driven by the rapid advances in the applications and accuracy of AI through increasingly complex algorithms and models; this, in turn, has spurred research into developing specialized hardware AI accelerators. The rapid pace of the advances makes it easy to miss the forest for the trees: they are often developed and evaluated in a vacuum without considering the full application environment in which they must eventually operate. In this paper, we deploy and characterize Face Recognition, an AI-centric edge video analytics application built using open source and widely adopted infrastructure and ML tools. We evaluate its holistic, end-to-end behavior in a production-size edge data center and reveal the “AI tax” for all the processing that is involved. Even though the application is built around state-of-the-art AI and ML algorithms, it relies heavily on pre- and post-processing code which must be executed on a general-purpose CPU. As AI-centric applications start to reap the acceleration promised by so many accelerators, we find they impose stresses on the underlying software infrastructure and the data center’s capabilities: storage and network bandwidth become major bottlenecks with increasing AI acceleration. By not having to serve a wide variety of applications, we show that a purpose-built edge data center can be designed to accommodate the stresses of accelerated AI at 15% lower TCO than one de-rived from homogeneous servers and infrastructure. We also discuss how our conclusions generalize beyond Face Recognition as many AI-centric applications at the edge rely upon the same underlying software and hardware infrastructure.

Paper
P. Mattson, et al., “MLPerf: An Industry Standard Benchmark Suite for Machine Learning Performance,” IEEE Micro, vol. 40, no. 2, pp. 8-16, 2020.Abstract
In this article, we describe the design choices behind MLPerf, a machine learning performance benchmark that has become an industry standard. The first two rounds of the MLPerf Training benchmark helped drive improvements to software-stack performance and scalability, showing a 1.3× speedup in the top 16-chip results despite higher quality targets and a 5.5× increase in system scale. The first round of MLPerf Inference received over 500 benchmark results from 14 different organizations, showing growing adoption.

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