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Graphics processing units (GPUs) are being widely used as co-processors in many application domains to accelerate general-purpose workloads that are computationally intensive, known as GPGPU computing. Real-time multi-tasking support is a critical requirement for many emerging GPGPU computing domains. However, due to the asynchronous and non-preemptive nature of GPU processing, in multi-tasking environments, tasks with higher priority may be blocked by lower priority tasks for a lengthy duration. This severely harms the system's timing predictability and is a serious impediment limiting the applicability of GPGPU in many real-time and embedded systems. In this paper, we present an efficient GPGPU preemptive execution system (GPES), which combines user-level and driverlevel runtime engines to reduce the pending time of high-priority GPGPU tasks that may be blocked by long-freezing low-priority competing workloads. GPES automatically slices a long-running kernel execution into multiple subkernel launches and splits data transaction into multiple chunks at user-level, then inserts preemption points between subkernel launches and memorycopy operations at driver-level. We implement a prototype of GPES, and use real-world benchmarks and case studies for evaluation. Experimental results demonstrate that GPES is able to reduce the pending time of high-priority tasks in a multitasking environment by up to 90% over the existing GPU driver solutions, while introducing small overheads.

Deep Neural Networks (DNNs) have been widely applied in many autonomous systems such as autonomous driving and robotics for their state-of-the-art, even human-competitive accuracy in cognitive computing tasks. Recently, DNN testing has been intensively studied to automatically generate adversarial examples, which inject small-magnitude perturbations into inputs to test DNNs under extreme situations. While existing testing techniques prove to be effective, particularly for autonomous driving, they mostly focus on generating digital adversarial perturbations, e.g., changing image pixels, which may never happen in physical world. Thus, there is a critical missing piece in the literature on autonomous driving testing: understanding and exploiting both digital and physical adversarial perturbation generation for impacting steering decisions. In this paper, we propose a systematic physical-world testing approach, namely DeepBillboard, targeting at a quite common and practical driving scenario: drive-by billboards. DeepBillboard is capable of generating a robust and resilient printable adversarial billboard test, which works under dynamic changing driving conditions including viewing angle, distance, and lighting. The objective is to maximize the possibility, degree, and duration of the steeringangle errors of an autonomous vehicle driving by our generated billboard with adversarial perturbations. We have extensively evaluated the efficacy and robustness of DeepBillboard through conducting both experiments with digital perturbations and physical-world case studies. The digital experimental results show that DeepBillboard is effective for various steering models and scenes. Furthermore, the physical case studies demonstrate that DeepBillboard is sufficiently robust and resilient for generating physical-world adversarial billboard tests for real-world driving under various weather conditions, being able to mislead the average steering angle error up to 26.44 degrees. To the best of our knowledge, this is the first study demonstrating the possibility of generating realistic and continuous physical-world tests for practical autonomous driving systems; moreover, the basic DeepBillboard approach can be directly generalized to a variety of other physical entities/surfaces along the curbside, e.g., a graffiti painted on a wall.

Graphics processing units are being widely used in embedded systems as they can achieve high performance and energy efficiency. In such systems, the problem of computation and data mapping for multiple applications while minimizing the completion time is quite challenging due to a large size of the policy space, including heterogeneous application characteristics, complex application structure, data communication costs, and data partitioning. To achieve fast competition time, a fine-grain mapping framework that explores a set of critical factors is needed for heterogeneous embedded systems. In this paper, we consider this mapping problem by presenting a theoretical framework that yields an optimal integer programming solution. Moreover, based upon several interesting measurements-based case studies, we design three practical mapping algorithms with low time complexity, each of which explores a specific set of factors that may affect the completion time performance. We evaluated the proposed algorithms by implementing them on a real heterogeneous system and using a large set of popular benchmarks for evaluation. Experimental results demonstrate that our proposed algorithms can achieve up to 30% faster completion time compared to the state-of-the-art mapping techniques, and can perform consistently well across different workloads.

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