Deep neural networks (DNNs) are being widely used in various computer vision tasks as they can achieve very high accuracy. However, the large number of parameters employed in DNNs can result in long inference times for vision tasks, thus making it even more challenging to deploy them in the compute- and memory-constrained mobile/edge devices. To boost the inference of DNNs, some existing works employ compression (model pruning or quantization) or enhanced hardware. How-ever, most prior works focus on improving model structure and implementing custom accelerators. As opposed to the prior work, in this paper, we target the video data that are processed by edge devices, and study the similarity between frames. Based on that, we propose two runtime approaches to boost the performance of the inference process, while achieving high accuracy.Specifically, considering the similarities between successive video frames, we propose a frame-level compute reuse algorithm based on the motion vectors of each frame. With frame-level reuse, we are able to skip 53% of frames in inference with negligible overhead and remain within less than 1% mAP (accuracy) drop for the object detection task. Additionally, we implement a partial inference scheme to enable region/tile-level reuse. Our experiments on a representative mobile device (Pixel 3 Phone) show that the proposed partial inference scheme achieves 2 × speedup over the baseline approach that performs full inference on every frame. We integrate these two data reuse algorithms to accelerate the neural network inference and improve its energy efficiency. More specifically, for each frame in the video, we can dynamically select between (i) performing a full inference, (ii) performing a partial inference, or (iii) skipping the inference altogether. Our experimental evaluations using six different videos reveal that the proposed schemes are up to 80% (56% on average) energy efficient and 2.2× performance efficient compared to the conventional scheme, which performs full inference, while losing less than 2% accuracy. Additionally, the experimental analysis indicates that our approach outperforms the state-of-the-art work with respect to accuracy and/or performance/energy savings.

As Point Clouds (PCs) gain popularity in processing millions of data points for 3D rendering in many applications, efficient data compression becomes a critical issue. This is because compression is the primary bottleneck in minimizing the latency and energy consumption of existing PC pipelines. Data compression becomes even more critical as PC processing is pushed to edge devices with limited compute and power budgets. In this paper, we propose and evaluate two complementary schemes, intra-frame compression and inter-frame compression, to speed up the PC compression, without losing much quality or compression efficiency. Unlike existing techniques that use sequential algorithms, our first design, intra-frame compression, exploits parallelism for boosting the performance of both geometry and attribute compression. The proposed parallelism brings around $43.7 \times$ performance improvement and 96.6% energy savings at a cost of $1.01 \times$ larger compressed data size. To further improve the compression efficiency, our second scheme, inter-frame compression, considers the temporal similarity among the video frames and reuses the attribute data from the previous frame for the current frame. We implement our designs on an NVIDIA Jetson AGX Xavier edge GPU board. Experimental results with six videos show that the combined compression schemes provide $34.0 \times$ speedup compared to a state-of-the-art scheme, with minimal impact on quality and compression ratio.

IoT devices can be used to complete a wide array of physical tasks, but due to factors such as low computational resources and distributed physical deployment, they are susceptible to a wide array of faulty behaviors. Many devices deployed in homes, vehicles, industrial sites, and hospitals carry a great risk of damage to property, harm to a person, or breach of security if they behave faultily. We propose a general fault handling system named IoTRepair, which shows promising results for effectiveness with limited latency and power overhead in an IoT environment. IoTRepair dynamically organizes and customizes fault-handling techniques to address the unique problems associated with heterogeneous IoT deployments. We evaluate IoTRepair by creating a physical implementation mirroring a typical home environment to motivate the effectiveness of this system. Our evaluation showed that each of our fault-handling functions could be completed within 100 milliseconds after fault identification, which is a fraction of the time that state-of-the-art fault-identification methods take (measured in minutes). The power overhead is equally small, with the computation and device action consuming less than 30 milliwatts. This evaluation shows that IoTRepair not only can be deployed in a physical system, but offers significant benefits at a low overhead.

Hologram processing is the primary bottleneck and contributes to more than 50% of energy consumption in battery-operated augmented reality (AR) headsets. Thus, improving the computational efficiency of the holographic pipeline is critical. The objective of this paper is to maximize its energy efficiency without jeopardizing the hologram quality for AR applications. Towards this, we take the approach of analyzing the workloads to identify approximation opportunities. We show that, by considering various parameters like region of interest and depth of view, we can approximate the rendering of the virtual object to minimize the amount of computation without affecting the user experience. Furthermore, by optimizing the software design flow, we propose HoloAR, which intelligently renders the most important object in sight to the clearest detail, while approximating the computations for the others, thereby significantly reducing the amount of computation, saving energy, and gaining performance at the same time. We implement our design in an edge GPU platform to demonstrate the real-world applicability of our research. Our experimental results show that, compared to the baseline, HoloAR achieves, on average, 2.7 × speedup and 73% energy savings.

The emergence of virtual reality (VR) and augmented reality (AR) has revolutionized our lives by enabling a 360° artificial sensory stimulation across diverse domains, including, but not limited to, sports, media, healthcare, and gaming. Unlike the conventional planar video processing, where memory access is the main bottleneck, in 360° VR videos the compute is the primary bottleneck and contributes to more than 50% energy consumption in battery-operated VR headsets. Thus, improving the computational efficiency of the video processing pipeline in a VR is critical. While prior efforts have attempted to address this problem through acceleration using a GPU or FPGA, none of them has analyzed the 360° VR pipeline to examine if there is any scope to optimize the computation with known techniques such as memoization.Thus, in this paper, we analyze the VR computation pipeline and observe that there is significant scope to skip computations by leveraging the temporal and spatial locality in head orientation and eye correlations, respectively, resulting in computation reduction and energy efficiency. The proposed Déjà View design takes advantage of temporal reuse by memoizing head orientation and spatial reuse by establishing a relationship between left and right eye projection, and can be implemented either on a GPU or an FPGA. We propose both software modifications for existing compute pipeline and microarchitectural additions for further enhancement. We evaluate our design by implementing the software enhancements on an NVIDIA Jetson TX2 GPU board and our microarchitectural additions on a Xilinx Zynq-7000 FPGA model using five video workloads. Experimental results show that Déjà View can provide 34% computation reduction and 17% energy saving, compared to the state-of-the-art design.

Billions of Internet-of-Things (IoT) devices such as sensors, actuators, computing units, etc., are connected to form IoT platforms. However, it is observed that such hardware platforms today spend a significant proportion of their energy in communication between the CPU and the sensors (which are controlled by micro-controller unit (MCU)). Motivated by this observation, two simple, yet effective, optimizations are proposed to minimize the energy consumption. The first optimization, called Batching, interrupts the CPU after collecting multiple sensor data points at the MCU (instead of only 1), and thus, minimizes the interrupt overheads. The second optimization, called Computation Offloading to MCU (COM), offloads app-specific computations to the MCU to minimize data transfer overheads, and makes use of the relatively low energy footprint, and low-compute capabilities of the MCU in place of the CPU in the hub. However, questions such as why these two schemes are needed, where the energy benefit comes from, which IoT apps are suitable for these optimizations, etc., remain unclear. To better understand the Batching and COM approaches towards energy efficiency in IoT app executions, we characterize ten representative workloads on a Raspberry Pi and ESP8266 MCU platform, and evaluate the energy savings using these two optimizations and illustrate that for light-weight workloads (where COM is applicable), Batching and COM reduce the energy consumption by 52% and 85%, respectively when compared to the baseline. And for heavy-weight apps (where COM is not possible due to limited capacity of MCU), by offloading the light-weight apps and batching for the heavy-weight, Batching + COM (BCOM) benefits 10% energy savings compared to the baseline.

Video broadcast and streaming are among the most widely used applications for edge devices. Roughly 82% of the mobile internet traffic is made up of video data. This is likely to worsen with the advent of 5G that will open up new opportunities for high resolution videos, virtual and augmented reality-based applications. The raw video data produced and consumed by edge devices is considerably higher than what is transmitted out of them. This leads to huge memory bandwidth and energy requirements from such edge devices. Therefore, optimizing the memory bandwidth and energy consumption needs is imperative for further improvements in energy efficiency of such edge devices. In this paper, we propose two mechanisms for on-the-fly compression and approximation of raw video data that is generated by the image sensors. The first mechanism, MidVB, performs lossless compression of the video frames coming out of the sensors and stores the compressed format into the memory. The second mechanism, Distill, builds on top of MidVB and further reduces memory consumption by approximating the video frame data. On an average, across 20 raw videos, MidVB and Distill are able to reduce the memory bandwidth by 43% and 72%, respectively, over the raw representation. They outperform a well known memory saving mechanism by 7% and 36%, respectively. Furthermore, MidVB and Distill reduce the energy consumption by 40% and 67%, respectively, over the baseline.

Today's mobile platforms have grown in sophistication to run a wide variety of frame-based applications. To deliver better QoS and energy efficiency, these applications utilize multi-flow execution, which exploits hardware-level parallelism across participating accelerators in the SoC. Our study shows that multi-flow execution increases memory pressure, and motivates us to propose a rate-based memory-scheduling scheme, called FLOSS, that considers a flow, individual frames of a flow, and any sharing of IPs across concurrent flows to schedule memory requests. Experimental results indicate that FLOSS provides 12% QoS improvement over baseline FR-FCFS scheme, and outperforms two QoS-aware schemes in multi-flow execution scenarios.

In this paper, we conduct a systematic analysis to show that existing CPU optimizations targeting scientific/server workloads are not always well suited for mobile apps. In particular, we observe that the well-known and very important concept of identifying and accelerating individual critical instructions in workloads such as SPEC, are not as effective for mobile apps. Several differences in mobile app characteristics including (i) dependencies between critical instructions interspersed with non-critical instructions in the dependence chain, (ii) temporal proximity of the critical instructions in the dynamic stream, and (iii) the bottleneck shifting to the front from the rear of the datapath pipeline, are key contributors to the ineffectiveness of traditional criticality based optimizations. Instead, we propose the concept of Critical Instruction Chains (CritICs) - which are short, critical and self contained sequences of instructions, for aggregate level optimization. With motivating results, we show that an offline profiler/analysis framework can easily identify these CritICs, and we propose a very simple software mechanism in the compiler that exploits ARM's 16-bit ISA format to nearly double the fetch bandwidth of these instructions. We have implemented this entire framework - both profiler and compiler passes, and evaluated its effectiveness for 10 popular apps from the Play Store. Experimental evaluations show that our approach is much more effective than two previously studied criticality optimizations, yielding a speedup of 12.65%, and energy savings of 15% in the CPU (translating to a system wide energy savings of 4.6%), requiring very little additional hardware support.

Video streaming has become the most common application in handhelds and this trend is expected to grow in future to account for about 75% of all mobile data traffic by 2021. Thus, optimizing the performance and energy consumption of video processing in mobile devices is critical for sustaining the handheld market growth. In this paper, we propose three complementary techniques, race-to-sleep, content caching and display caching, to minimize the energy consumption of the video processing flows. Unlike the state-of-the-art frame-by-frame processing of a video decoder, the first scheme, race-to-sleep, uses two approaches, called batching of frames and frequency boosting to prolong its sleep state for saving energy, while avoiding any frame drops. The second scheme, content caching, exploits the content similarity of smaller video blocks, called macroblocks, to design a novel cache organization for reducing the memory pressure. The third scheme, in turn, takes advantage of content similarity at the display controller to facilitate display caching further improving energy efficiency. We integrate these three schemes for developing an end-to-end video processing framework and evaluate our design on a comprehensive mobile system design platform with a variety of video processing workloads. Our evaluations show that the proposed three techniques complement each other in improving performance by avoiding frame drops and reducing the energy consumption of video streaming applications by 21%, on average, compared to the current baseline design.