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Satisfying timing constraints of real-time databases

JOURNAL OF SYSTEMS AND SOFTWARE 1998年第1期41卷 63-73页

作者： Vrbsky, SV Tomic, S Univ Alabama Dept Comp Sci Tuscaloosa AL 35487 USA

A real-time database has deadlines for processing transactions. Approximate query processing (AQP) has been presented as a strategy to satisfy these timing constraints by providing approximate answers to queries at the deadline instead of missing deadlines. In order to produce approximate answers, semantic information is maintained about the database and a computational overhead is required. In this paper the performance of AQP is examined to determine its effect on satisfying the timing constraints of real-time databases. Query and update transactions are modeled as periodic tasks with hard deadlines. A lock-based concurrency control is used and the effect of workload characteristics, such as the scheduling algorithm, the number of transactions and the percentage of update transactions, are examined. We compare the number of missed deadlines and approximate answers produced during AQP to the number of missed deadlines occurring during traditional query processing (TQP). Results demonstrate that despite the overhead, fewer deadlines are missed during approximate query processing than during TQP. (C) 1998 Elsevier Science Inc. All rights reserved.

关键词： approximation approximate query processing imprecise computation performance evaluation real-time databases

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Compositional real-time scheduling framework for periodic reward-based task model

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JOURNAL OF SYSTEMS AND SOFTWARE 2013年第6期86卷 1712-1724页

作者： Tchamgoue, Guy Martin Kim, Kyong Hoon Jun, Yong-Kee Lee, Wan Yeon Gyeongsang Natl Univ Dept Informat Jinju South Korea Dongduk Womens Univ Dept Comp Sci Seoul South Korea

As the size and complexity of embedded software systems increase, compositional real-time scheduling framework is widely accepted as means to build large and complex systems. A compositional real-time scheduling framework proposes to decompose a system into independent subsystems and provides ways to assemble them into a flexible hierarchical real-time scheduling system while guaranteeing the internal real-time requirements of each subsystem. In this paper, we consider the imprecise reward-based periodic task model in compositional scheduling framework. Thus, we introduce the imprecise periodic resource model to characterize the imprecise resource allocations provided by the system to a single component, and the interface model to abstract the imprecise real-time requirements of the component. The schedulability of mandatory parts is also analyzed to meet the minimum requirement of tasks. Finally, we provide a scheduling algorithm to guarantee a certain amount of reward, which makes it feasible to efficiently compose multiple imprecise components. (C) 2013 Elsevier Inc. All rights reserved.

关键词： Compositional and hierarchical real-time scheduling Interface model Resource model imprecise computation Reward function

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Satisfying temporal consistency constraints of real-time databases

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JOURNAL OF SYSTEMS AND SOFTWARE 1999年第1期45卷 45-60页

作者： Vrbsky, SV Tomic, S Univ Alabama Dept Comp Sci Tuscaloosa AL 35487 USA

In addition to timing constraints, a real-time database has temporal consistency constraints for its temporal data. The temporal consistency constraints require the data to represent a state of the real-world that is up-to-date and also require data to represent past states of the real-world with values that are close in time. Factors, such as concurrency control, can cause transactions to miss their deadlines and data to become temporally inconsistent. Approximate query processing (AQP) has been proposed as a strategy to satisfy the timing constraints of real-time databases. Approximate answers are provided by AQP if it is not possible to produce an exact answer by a specified deadline. In this paper, we examine the temporal consistency of the data during traditional and AQP. Four metrics of temporal consistency are utilized to compare the age and dispersion of the data during traditional query processing (TQP) versus approximate query processing. Simulation results identify factors, such as the concurrency control algorithm, the number of transactions and the percentage of query transactions, that affect the temporal inconsistency of the data. (C) 1998 Elsevier Science Inc. All rights reserved.

关键词： approximate query processing imprecise computation real-time databases temporal consistency

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Approximate Multipliers Using Bio-Inspired Algorithm

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JOURNAL OF ELECTRICAL ENGINEERING & TECHNOLOGY 2021年第1期16卷 559-568页

作者： Senthilkumar, K. K. Kumarasamy, Kunaraj Dhandapani, Vaithiyanathan Prince Shri Venkateshwara Padmavathy Engn Coll Chennai Tamil Nadu India Loyola ICAM Coll Engn & Technol LICET Chennai Tamil Nadu India Natl Inst Technol Delhi Delhi India

As most of the real-world problems are imprecise, dedicating a lot of hardware for precise computations is futile for low-power applications and few applications where the precision is not of paramount importance. For such applications an imprecise computational block is sufficient if it has other performance benefits like low power and low area. We propose Constrained Cartesian Genetic Programming (CCGP), a variant of CGP to evolve lower order imprecise multipliers and further the higher order multipliers are constructed from them. Gate-level architectures for 2 x 2, 3 x 2, 3 x 3 and 4 x 4 imprecise multipliers are evolved. Also, we propose few partitioning methodologies for the construction of higher order multipliers using the evolved imprecise lower order multipliers. The constructed evolved-partitioned multiplier (EPM) of orders 8 x 8 and 16 x 16 has significant performance benefits over the existing multiplier architectures in terms of cell area and power. The circuits are synthesized using Cadence SoC Encounter(R) using TSMC 180 nm standard cell library. The 16-bit EPMs show a maximum power reduction of 33% compared to other truncated multipliers and an area improvement of 2%.

关键词： Evolutionary computation Cartesian Genetic Programming imprecise computation Low power arithmetic Recursive multiplier

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Logical rules of visual brain: From anatomy through neurophysiology to cognition

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COGNITIVE SYSTEMS RESEARCH 2010年第1期11卷 53-66页

作者： Przybyszewski, Andrzej W. Univ Massachusetts Med Ctr Dept Neurol Worcester MA 01655 USA McGill Univ Dept Psychol Montreal PQ Canada

Humans can easily recognize objects as complex as faces even if they have not seen them in such conditions or context before. It seems that perceptually we are insensitive to the exact properties of an object's parts but the same parts in different configurations or contexts may introduce contradictory effects. From a computational point of view, we are often insensitive to changes of some symbols, but the same symbols may lead to different classification of the same object. In present work we are looking for the anatomical and neurophysiological basis of these perceptual effects. We describe interactions between parts and their configurations in different areas of the visual brain on the basis of a single cell electrophysiological activity in the thalamus, and cortical areas V1 and V4. Our model is based on feedforward (FF) and feedback (FB) interactions between these areas. In the retina and thalamus simple light spots are classified, V1 is the first area extracting edge orientation and V4 is the first area sensitive to simple shapes. The FF pathways combine properties extracted in each area into hypothetical objects. Area V1 presents concepts of orientations, while area V4 presents concepts of a simple shape. The FB pathways are responsible for comparison of the learned concepts with extracted object's properties-they form predictions. In each area structure related predictions are tested against hypothesis. We formulate a theory in which different visual stimuli are described through their condition attributes: responses in LGN, V1, and V4 neurons are divided into several ranges and are treated as decision attributes. Applying rough set theory [Pawlak, Z. (1991). Rough sets-theoretical aspects of reasoning about data. Boston, London, Dordrecht: Kluwer Academic Publishers] we have divided our stimuli into area dependent equivalent classes. We propose that relationships between decision rules in each area are determined by two different logical rules: "driver logi

关键词： Rough set theory imprecise computation Bottom-up fusion Top-down extension Receptive field logic Fuzzy brain

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Real-time arithmetic unit

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REAL-TIME SYSTEMS 2006年第1期34卷 53-79页

作者： Mora-Mora, Higinio Mora-Pascual, Jeronimo Manuel Garcia-Chamizo, Juan Jimeno-Morenilla, Antonio Univ Alicante DTIC SPA Lab E-03080 Alicante Spain

In this paper we discuss the paradigm of real-time processing on the lower level of computing systems. An arithmetical unit based on this principle containing addition, multiplication, division and square root operations is described. The development of the computation operators model is based on the imprecise computation paradigm and defines the concept of the adjustable calculation of a function that manages delay and the precision of the results as an inherent and parameterized characteristic. The arithmetic function design is based on well-known algorithms and offers progressive improvement in the results. Advantages in the predictability of calculations are obtained by means of processing groups of k-bits atomically and by using look-up tables. We report an evaluation of the operations in path time, delay and computation error. Finally, we present an example of our real-time architecture working in a realistic context.

关键词： real-time imprecise computation computer arithmetic multiple-precision arithmetic

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Mixed Criticality Reward-Based Systems Using Resource Reservation

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IEEE ACCESS 2024年 12卷 49134-49150页

作者： Ali, Amjad Zeb, Shah Alruwaili, Madallah Khattak, Asad Masood Hayat, Bashir Kim, Ki-Il Univ Swat Dept Comp & Software Technol Swat 19120 Khyber Pakhtunk Pakistan Jouf Univ Coll Comp & Informat Sci Sakaka 2014 Aljouf Saudi Arabia Zayed Univ Coll Technol Innovat Dubai U Arab Emirates Inst Management Sci Ctr Excellence IT Peshawar 25000 Khyber Pakhtunk Pakistan Chungnam Natl Univ Dept Comp Sci & Engn Daejeon 34134 South Korea

Real-time systems mostly interact with the external world and each input operation must meet predetermined deadlines to be useful. However, in many real-time applications, a partial result is also acceptable. We developed a reward-based mixed criticality system based on the resource reservation approach to address the problem of ensuring the effective execution of low- and high-criticality tasks in both low- and high modes, even under heavy workloads. Using dedicated servers with pessimistic resource allocation for each high criticality task ensured their execution in both modes unaffected by low criticality tasks. The surplus resources are reclaimed and assigned to low critical tasks' server by utilizing a greedy reclamation of unused bandwidth (GRUB) algorithm. Three strategies were suggested for server allocation to low criticality tasks: a dedicated server for all low criticality tasks, a single server for each low criticality task, and two servers (mandatory and optional) for each low criticality task. Our analysis revealed efficiency of the first approach by achieving 100% schedulability at a 1.1 target utilization, scheduling 20% and 50% more task sets than the second and third approaches, respectively. Moreover, the effectiveness of the proposed approach over existing imprecise mixed criticality approaches were demonstrated through comprehensive experimentation.

关键词： Task analysis Real-time systems Servers Processor scheduling Job shop scheduling Multicore processing Schedules Greedy algorithms Resource management Greedy reclamation imprecise computation imprecise mixed criticality (IMC) systems mixed criticality systems real-time systems resource reservation reward-based scheduling servers

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Resource-Constrained Scheduling Algorithms for Stochastic Independent Tasks With Unknown Probability Distribution

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ALGORITHMICA 2023年第8期85卷 2363-2394页

作者： Gao, Yiqin Robert, Yves Vivien, Frederic Shanghai Jiao Tong Univ Shanghai Peoples R China ENS Lyon & Inria Lab LIP Lyon France Univ Tennessee Knoxville Knoxville TN 37996 USA

This work introduces scheduling algorithms to maximize the expected number of independent tasks that can be executed on a parallel platform within a given budget and under a deadline constraint. The main motivation for this problem comes from imprecise computations, where each job has a mandatory part and an optional part, and the objective is to maximize the number of optional parts that are successfully executed, in order to improve the accuracy of the results. The optional parts of the jobs represent the independent tasks of our problem. Task execution times are not known before execution;instead, the only information available to the scheduler is that they obey some (unknown) probability distribution. The scheduler needs to acquire some information before deciding for a cutting threshold: instead of allowing all tasks to run until completion, one may want to interrupt long-running tasks at some point. In addition, the cutting threshold may be reevaluated as new information is acquired when the execution progresses further. This work presents several algorithms to determine a good cutting threshold, and to decide when to re-evaluate it. In particular, we use the Kaplan-Meier estimator to account for tasks that are still running when making a decision. The efficiency of our algorithms is assessed through an extensive set of simulations with various budget and deadline values, and ranging over 13 probability distributions. In particular, the AutoPerSurvival(40%,0.005) strategy is proved to have a performance of 77% compared to the upper bound even in the worst case. This shows the robustness of our strategy.

关键词： Stochastic tasks Independent tasks imprecise computation Resource allocation Scheduling Kaplan-Meier estimator

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Designing energy-efficient imprecise adders with multi-bit approximation

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MICROELECTRONICS JOURNAL 2019年 89卷 41-55页

作者： Tajasob, Sarvenaz Rezaalipour, Morteza Dehyadegari, Masoud KN Toosi Univ Technol Fac Comp Engn Tehran Iran

Since early 2000s, achieving significant energy-efficiency for CMOS VLSI circuit design has become more difficult. Approximate computing is a hopeful solution for enhancing power-efficiency in error-tolerant applications. In such systems, adders play an essential role and mainly contribute to the system's total power and area consumption. Many proposals have been introduced in the literature that build large adders while using novel low power full adder structure as its building blocks. However, single-bit structure approximation, only limits the design space of approximate adders. And leads to a poor trade-off between accuracy and power dissipation. This paper proposes a novel approach for design of multi-bit adders, based on three novel approximate 2-bit adder circuits. Simulation results demonstrates that the proposed adders consume less area and power than the state-of-the-art approximate adders. Up to 80% power improvements are attainable for the proposed designs as compared with the baseline adders.

关键词： imprecise computation Multi-bit approximate adders

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Scheduling parallel and distributed processing for automotive data stream management system

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JOURNAL OF PARALLEL AND DISTRIBUTED COMPUTING 2017年 109卷 286-300页

作者： Rho, Jaeyong Azumi, Takuya Nakagawa, Mayo Sato, Kenya Nishio, Nobuhiko Ritsumeikan Univ Grad Sch Informat Sci & Engn Shiga 5258577 Japan Ritsumeikan Univ Coll Informat Sci & Engn Shiga 5258577 Japan Osaka Univ Grad Sch Engn Sci Toyonaka Osaka 5608531 Japan Doshisha Univ Mobil Res Ctr Kyoto 6028580 Japan

In this paper, to analyze end-to-end timing behavior in heterogeneous processor and network environments accurately, we adopt and modify a heterogeneous selection value on communication contention (HSV_CC) algorithm, which can synchronize tasks and messages simultaneously, for stream processing distribution. In order to adapt the concepts of a static algorithm like HSV_CC to automotive data stream management system (DSMSs), one must first address three issues: (i) previous task and message schedules might lead to less efficient resource usages in this scenario;(ii) the conventional method to determine the task scheduling order may not be best suited to deal with stream processing graphs, and;(iii) there is a need to be able to schedule tasks with time-varying computational requirements efficiently. To address (i), we propose the heterogeneous value with load balancing and communication contention (HVLB_CC) (A) algorithm, which considers load balancing in addition to the parameters considered by the HSV_CC algorithm. We propose HVLB_CC (B) to address issue (ii). HVLB_CC (B) can deal with stream processing task graphs and more various directed acyclic graphs to prevent assigning a higher priority to successor tasks. In addition, to address issue (iii), we propose HVLB_CC_IC. To schedule tasks more efficiently with various computation times, HVLB_CC_IC utilizes schedule holes left in processors. These idle time slots can be used for the execution of an optional part to generate more precise data results by applying imprecise computation models. Experimental results demonstrate that the proposed algorithms improve minimum schedule length, accuracy, and load balancing significantly compared to the HSV_CC algorithm. In addition, the proposed HVLB_CC (B) algorithm can schedule more varied task graphs without reducing performance, and, using imprecise computation models, HVLB_CC_IC yields higher precision data than HVLB_CC without imprecise computation models. (C) 2017 Else

关键词： Automotive data stream management system Heterogeneous processor and network Load balancing List scheduling imprecise computation

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