Exact Response Time Research Articles

Exact Response Time Analysis of Preemptive Priority Scheduling with Switching Overhead

The study of preemptive scheduling is essential to computer systems [15, 12, 3, 4]. Motivated by this, decades of queueing theory research have been done on the subject [19, 18, 16, 13, 21, 8, 17, 2, 11, 20, 10, 1]. However, almost all queuing theoretic literature on preemptive scheduling concerns systems without switching overhead - pausing or resuming a job is assumed to be instant. Practically speaking, switching in computer systems incurs some overhead [14], which causes a divide between models in research and the real world.

Efficient Exact Response Time Analysis for Fixed Priority Scheduling in Lowest Priority First-Based Feasibility Tests

The exact response time analysis for fixed priority scheduling (FPS) in the lowest priority first-based feasibility tests is commonly required as a part of system design tools. This letter proposes an efficient method for this, which we named incremental lower bound (ILB) calculation method. Compared to the best algorithm that has been known so far, which is the incremental calculation method, ILB reduces the feasibility test iterations/run times by more than 38% and 20% regardless of varying utilization and the number of tasks in task sets.

Machine learning analysis to automatically measure response time of pharyngeal swallowing reflex in videofluoroscopic swallowing study

To evaluate clinical features and determine rehabilitation strategies of dysphagia, it is crucial to measure the exact response time of the pharyngeal swallowing reflex in a videofluoroscopic swallowing study (VFSS). However, measuring the response time of the pharyngeal swallowing reflex is labor-intensive and particularly for inexperienced clinicians, it can be difficult to measure the brief instance of the pharyngeal swallowing reflex by VFSS. To accurately measure the response time of the swallowing reflex, we present a novel framework, able to detect quick events. In this study, we evaluated the usefulness of machine learning analysis of a VFSS video for automatic measurement of the response time of a swallowing reflex in a pharyngeal phase. In total, 207 pharyngeal swallowing event clips, extracted from raw VFSS videos, were annotated at the starting point and end point of the pharyngeal swallowing reflex by expert clinicians as ground-truth. To evaluate the performance and generalization ability of our model, fivefold cross-validation was performed. The average success rates of detection of the class “during the swallowing reflex” for the training and validation datasets were 98.2% and 97.5%, respectively. The average difference between the predicted detection and the ground-truth at the starting point and end point of the swallowing reflex was 0.210 and 0.056 s, respectively. Therefore, the response times during pharyngeal swallowing reflex are automatically detected by our novel framework. This framework can be a clinically useful tool for estimating the absence or delayed response time of the swallowing reflex in patients with dysphagia and improving poor inter-rater reliability of evaluation of response time of pharyngeal swallowing reflex between expert and unskilled clinicians.

Exact response time analysis of fixed priority systems based on sporadic servers

Abstract Real-time servers have been widely explored in the scheduling literature to predictably execute aperiodic activities, as well as to allow hierarchical scheduling settings. As they facilitate timing isolation between different software components, there is a renewed interest for the adoption of fixed priority real-time servers in the automotive domain, as a way to implement more efficient reservation mechanisms than TDMA-based methods. In this paper, we focus on the Sporadic Server, which is the only fixed priority server supported by the POSIX standard. Despite its popularity, we realized that only sufficient schedulability conditions exist for real-time systems scheduled with a Sporadic Server. Thus, we develop a formal characterization of an exact response time analysis for fixed priority systems based on Sporadic Servers in a multi-level scheduling setting under preemptive scheduling. We then provide an experimental characterization of the schedulabilty improvement that can be obtained with respect to existing sufficient schedulability tests, proving the effectiveness of the proposed exact analysis.

Exact WCRT Analysis for Message-Processing Tasks on Gateway-Integrated In-Vehicle CAN Clusters

A typical automotive integrated architecture is a controller area network (CAN) cluster integrated by a central gateway. This study proposes a novel and exact worst-case response time (WCRT) analysis method for message-processing tasks in the gateway. We first propose a round search method to obtain lower bound on response time (LBRT) and upper bound on response time (UBRT), respectively. We then obtain the exact WCRT belonging to the scope of the LBRT and UBRT with an effective non-exhaustive exploration. Experimental results on a real CAN message set reveal that the proposed exact analysis method can reduce 99.99999% combinations on large-scale CAN clusters.

Response-Time Analysis of Engine Control Applications Under Fixed-Priority Scheduling

Engine control systems include computational activities that are triggered at predetermined angular values of the crankshaft, and therefore generate a workload that tends to increase with the engine speed. To cope with overload conditions, a common practice adopted by the automotive industry is to design such angular tasks with a set of modes that switch at given rotation speeds to adapt the computational demand. This paper presents an exact response time analysis for engine control applications consisting of periodic and engine-triggered tasks scheduled by fixed priority. The proposed analysis explicitly takes into account the physical constraints of the considered systems and is based on the derivation of dominant speeds, which are particular engine speeds that are proved to determine the worst-case behavior of engine-triggered tasks from a timing perspective. Experimental results are finally reported to validate the proposed approach and compare it against an existing sufficient test.

Efficient exact Boolean schedulability tests for fixed priority preemption threshold scheduling

Abstract Fixed priority preemption threshold scheduling (PTS) is effective in scalable real-time system design, which requires system tuning processes, where the performance of schedulability tests for PTS matters much. This paper proposes five methods for efficient exact Boolean schedulability tests for PTS, which returns the Boolean result that tells whether the given task is schedulable or not. We regard the sufficient test for fully preemptive fixed priority scheduling (FPS) and the early exit in the response time calculations as the conventional approach. We propose (1) a new sufficient test, (2) new initial values for the start/finish times, (3) pre-calculation of the interference time within the start time, (4) incremental start/finish time calculation, and (5) early exits in start/finish time calculations. These are based on some previous work for FPS. The new initial start time, pre-calculation, and the incremental calculations also can be used for the exact response time analysis for PTS. Our empirical results show that the overall proposed methods reduce the iteration count/run time of the conventional test by about 60%/40%, regardless of the number of tasks and the total utilization.

An exact schedulability test for fixed-priority preemptive mixed-criticality real-time systems

The current literature of fixed-priority scheduling algorithms relies on sufficient tests to determine if a set of mixed-criticality sporadic tasks is schedulable on a single processor. The drawback of these safe tests is their pessimism, a matter that could be solved if an exact schedulability analysis is used. However, because of the non-deterministic behavior of tasks in the mentioned setups, exact quantification of worst-case response times, needed for the test, is a difficult problem; more precisely, such a quantification needs evaluation of enormous sequences of job executions. The core problem is thus to merge such sequences to make the analysis practical. This paper, for the first time, gives an algorithm for exact worst-case response time characterization of mixed-criticality sporadic real-time tasks executing according to a given fixed-priority scheduler. We use a set of techniques which carefully consider the task properties and their relation to the worst scenarios to prune the analysis state space. We also show an interesting result that if an exact schedulability test is used, the Audsley's optimal priority assignment algorithm is not applicable to the mixed-criticality case. Accordingly, we need new priority assignment algorithms to work with the exact test; we give a simple task priority assignment algorithm to this aim. The performance of the proposed exact test (in terms of time complexity) is examined and the effectiveness of some heuristic priority assignment algorithms using the test (in terms of the ratio of task sets which are deemed schedulable) are compared.

Exact Response Time Analysis for Fixed Priority Memory-Processor Co-Scheduling

Recent technological advances have led to an increasing gap between memory and processor performance, since memory bandwidth is progressing at a much slower pace than processor bandwidth. Pre-fetching techniques are traditionally used to bridge this gap and achieve high processor utilization while tolerating high memory latencies. Following this trend, new computational models have been proposed to split task execution in two consecutive phases: a memory phase in which the required instructions and data are pre-fetched to local memory (M-phase), and an execution phase in which the task is executed with no memory contention (C-phase). Decoupling memory and execution phases not only simplifies the timing analysis, but also allows a more efficient (and predictable) pipelining of memory and execution phases through proper co-scheduling algorithms. This paper takes a further step towards the design of smart co-scheduling algorithms for sporadic real-time tasks complying with the memory-computation (M/C) model, by proposing a theoretical framework aimed at tightly characterizing the schedulability improvement obtainable with the adopted M/C task model on single-core systems. In particular, a critical instant is identified for M/C tasks scheduled with fixed priority and an exact response time analysis with pseudo-polynomial complexity is provided. Then, we investigate the problem of priority assignment for M/C tasks, showing that a necessary condition to achieve optimality is to allow different priorities for the two phases. Our experiments show that the proposed techniques provide a significant schedulability improvement with respect to classic execution models, placing an important building block towards the design of more efficient partitioned multi-core systems.

Fast detection of blood gases by solution gated organic field effect transistors

We characterize the electrochemical stability of the organic semiconductor Dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) in aqueous solutions. Electrochemical stability of DNTT in solution is validated by cyclic voltammetry and demonstrated by solution gating of DNTT organic field effect transistors (OFETs). Then, we investigate the response time of DNTT OFETs to ammonia, a common blood gas. For bare OFETs, the response time to ammonia is 1–2s only. The exact response time depends on the DNTT film morphology; the fastest response is obtained for pronounced 3D (Volmer-Weber) growth. By comparing OFETs with and without a semipermeable parylene-C encapsulation layer, the influence of the capping on the response time is investigated. An encapsulation layer of 86 nm prolongs the response time to 100s, indicating that parylene-C acts as an efficient diffusion barrier for ammonia.

An <sc>fptas</sc> for Response Time Analysis of Fixed Priority Real-Time Tasks with Resource Augmentation

Response time analysis is required both for on-line admission of applications in dynamic systems and as an integral part of design tools for complex distributed real-time systems. We consider sporadic tasks with fixed-priorities and arbitrary deadlines to be executed upon a uniprocessor platform. Pseudo-polynomial time algorithms are known for computing exact worst-case response times for this task model. Nevertheless, the problem is known NP-hard and there cannot exist a constant approximation algorithm for response time computation, unless P=NP. We propose a fully polynomial time approximation scheme (FPTAS) for computing response time upper bounds under resource augmentation. The resource augmentation is defined as the processor speedup factor bounded by (1 + 1/k), where k <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">def</sup> [1 = ε]-1 for any constant ε ∈ (0;1), the FPTAS accuracy parameter. This algorithm is best possible in the sense that resource augmentation is indeed necessary for an efficient response time calculation.

Feasibility analysis under fixed priority scheduling with limited preemptions

Preemptive scheduling often generates a significant runtime overhead that may increase task worst-case execution times up to 40%, with respect to a fully non-preemptive execution. In small embedded systems, such an extra cost results in longer and more variable response times that can significantly affect the overall energy consumption, as well as the system predictability. Limiting preemptions is often possible without jeopardizing schedulability. Although several authors addressed schedulability analysis under different forms of limited preemptive scheduling, current results exhibit two major deficiencies: (i) The maximum lengths of the non-preemptive regions for each task are still unknown under fixed priorities; (i) The exact response time analysis for tasks with fixed preemption points is too complex. This paper presents the schedulability analysis of real-time tasks with non-preemptive regions, under fixed priority assignments. In particular, two different preemption models are considered: the floating and the fixed preemption point model. Under each model, the feasibility analysis is addressed by deriving simple and effective schedulability tests, as well as an algorithm for computing the maximum length of the non-preemptive regions for each task. Finally, simulation experiments are presented to compare the two models in terms of schedulability.

Approximation techniques for response-time analysis of static-priority tasks

We consider sporadic tasks with static priorities and constrained deadlines to be executed upon a uniprocessor platform. Pseudo-polynomial time algorithms are known for computing worst-case response times for this task model. Some applications require to evaluate efficiently upper bounds of response times. For this purpose, we propose parametric algorithms that allow to make a tradeoff between quality of results and computational effort according to an input accuracy parameter. In this paper, we present a parametric polynomial-time algorithm for computing upper bounds of worst-case response times, that is based on an improved fptas (Fully Polynomial Time Approximation Scheme). Then, we show that our bound does not achieve constant error bound in comparison with the exact worst-case response time. However, using the resource augmentation technique, we obtain a performance guarantee that allows to define a compromise between our response-time bound and processor capacity requirements. The algorithm average behavior is then analyzed through numerical experimentations.

An efficient response-time analysis for real-time transactions with fixed priority assignment

In the general context of tasks with offsets (general transactions), only exponential methods are known to calculate the exact worst-case response time (WCRT) of a task. The known pseudo-polynomial techniques give an upper bound of the WCRT. In this paper, we present a new worst-case response-time analysis technique (mixed method) for transactions scheduled by fixed priorities, and executing on a uniprocessor system. This new analysis technique gives a better (i.e. lower) pseudo-polynomial upper bound of the WCRT. The main idea is to combine the principle of exact calculation and the principle of approximation calculation, in order to decrease the pessimism of WCRT analysis, thus allowing improving the upper bound of the response time provided while preserving a pseudo-polynomial complexity. Then we define the Accumulative Monotonic property on which a necessary condition of feasibility is discussed. We also propose, to speed up the exact and mixed analysis, the dominated candidate task concept that allows reducing significantly the number of critical instants to study in an analysis.

A Response-Time Bound in Fixed-Priority Scheduling with Arbitrary Deadlines

Since worst case response times must be determined repeatedly during the interactive design of real-time application systems, repeated exact computation of such response times would slow down the design process considerably. In this research, we identify three desirable properties of estimates of the exact response times: continuity with respect to system parameters, efficient computability, and approximability. We derive a technique possessing these properties for estimating the worst-case response time of sporadic task systems that are scheduled using fixed priorities upon a preemptive uniprocessor.

Spacecraft Task Hierarchical Scheduling Analysis Within Fixed Priorities

在航天器自主控制结构中, 采用分层结构构建系统, 实现不同分组的软件互不影响执行. 针对固定优先级调度模型, 通过对分区可调度性和分区设计问题进行研究, 仔细考察了任务最大响应时间迭代计算过程, 提出了一种更为精确的求解算法; 在固定优先级任务利用率上限的基础上, 给出了分区任务可设计的判定条件; 通过利用价值函数, 给出了分区参数解析模型, 在此基础上, 提出了一种局部最优的设计方法来实现整个处理器的分区设计, 通过具体实例对所提出的分区分析和设计方法进行了验证.

Efficient Exact Schedulability Tests for Fixed Priority Real-Time Systems

Efficient exact schedulability tests are required both for on-line admission of applications to dynamic systems and as an integral part of design tools for complex distributed real-time systems. This paper addresses performance issues with exact response time analysis (RTA) for fixed priority preemptive systems. Initial values are introduced that improve the efficiency of the standard RTA algorithm (i) when exact response times are required, and (ii) when only exact schedulability need be determined. The paper also explores modifications to the standard RTA algorithm, including; the use of a response time upper bound to determine when exact analysis is needed, incremental computation aimed at faster convergence, and checking tasks in reverse priority order to identify unschedulable task sets early. The various initial values and algorithm implementations are compared by means of experiments on a PC recording the number of iterations required, and execution time measurements on a real-time embedded microprocessor. Recommendations are provided for engineers tasked with the problem of implementing exact schedulability tests, as part of on-line acceptance tests and spare capacity allocation algorithms, or as part of off-line system design tools.

Rate monotonic analysis: the hyperbolic bound

We propose a novel schedulability analysis for verifying the feasibility of large periodic task sets under the rate monotonic algorithm when the exact test cannot be applied on line due to prohibitively long execution times. The proposed test has the same complexity as the original Liu and Layland (1973) bound, but it is less pessimistic, thus allowing it to accept task sets that would be rejected using the original approach. The performance of the proposed approach is evaluated with respect to the classical Liu and Layland method and theoretical bounds are derived as a function of n (the number of tasks) and for the limit case of n tending to infinity. The analysis is also extended to include aperiodic servers and blocking times due to concurrency control protocols. Extensive simulations on synthetic tasks sets are presented to compare the effectiveness of the proposed test with respect to the Liu and Layland method and the exact response time analysis.

Note on the Maxnet Dynamics

A simple method is presented to derive the complete solution of the Maxnet network dynamics. Besides, the exact response time of the network is deduced.

Sample Size Determination for Cohort Studies under an Exponential Covariate Model with Grouped Data

Assuming that the exact response times of studied subjects are known, Taulbee and Symons 1983 used an exponential covariate model due to Feigl and Zelen 1965 for the hazard and derived a general sample size formula for more than two dose groups. It is very common, however, in practice that we examine the responses only periodically and therefore, we know only whether these responses occur or not during an interval. We call this type of data grouped data. On the basis of the same model assumption as that of Taulbee and Symons, this paper extends Taulbee and Symons' sample size formula to accomodate more than two dose groups with grouped data.