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Proceedings ArticleDOI

Synchronization protocols in distributed real-time systems

27 May 1996-pp 38-45
TL;DR: This paper considers distributed real-time systems with independent, periodic tasks and fixed-priority scheduling algorithms, and proposes three synchronization protocols and conducts simulation to compare their performance with respect to the two timing aspects.
Abstract: In many distributed real-time systems, the workload can be modeled as a set of periodic tasks, each of which consists of a chain of subtasks executing on different processors. Synchronization protocols are used to govern the release of subtasks so that the precedence constraints among subtasks are satisfied and the schedulability of the resultant system is analyzable. Tasks have different worst-case and average end-to-end response times when different protocols are used. In this paper, we consider distributed real-time systems with independent, periodic tasks and fixed-priority scheduling algorithms. We propose three synchronization protocols and conduct simulation to compare their performance with respect to the two timing aspects.
Citations
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Journal ArticleDOI
TL;DR: This paper presents the end-to-end utilization control (EUCON) algorithm that adaptively maintains desired CPU utilization through performance feedbacks loops based on a model predictive control approach that models utilization control on a distributed platform as a multivariable constrained optimization problem.
Abstract: An increasing number of distributed real-time systems face the critical challenge of providing quality of service guarantees in open and unpredictable environments. In particular, such systems often need to enforce utilization bounds on multiple processors in order to avoid overload and meet end-to-end deadlines even when task execution times are unpredictable. While recent feedback control real-time scheduling algorithms have shown promise, they cannot handle the common end-to-end task model where each task is comprised of a chain of subtasks distributed on multiple processors. This paper presents the end-to-end utilization control (EUCON) algorithm that adaptively maintains desired CPU utilization through performance feedbacks loops. EUCON is based on a model predictive control approach that models utilization control on a distributed platform as a multivariable constrained optimization problem. A multi-input-multi-output model predictive controller is designed based on a difference equation model that describes the dynamic behavior of distributed real-time systems. Both control theoretic analysis and simulations demonstrate that EUCON can provide robust utilization guarantees when task execution times deviate from estimation or vary significantly at runtime.

164 citations


Cites background or methods from "Synchronization protocols in distri..."

  • ...In the end-to-end scheduling approach [22], the deadline of an end-to-end task is divided into subdeadlines of its subtasks, and the problem of meeting the deadline is transformed to the problem of meeting the subdeadline of each subtask....

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  • ...We now formulate the utilization control problem in DRE systems....

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  • ...Network delay may be handled by treating each network link as a processor [22], or by considering the impact of worst-case network delay in subdeadline assignment....

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  • ...…Control in Distributed Real-Time Systems with End-to-End Tasks Chenyang Lu, Xiaorui Wang, and Xenofon Koutsoukos Complete Abstract: An increasing number of distributed real-time systems face the critical challenge of provid-ing quality of service guarantees in open and unpredictable environments....

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Proceedings ArticleDOI
23 Jun 2013
TL;DR: This paper aims to demonstrate the efforts towards in-situ applicability of EMMARM, which aims to provide real-time information about the physical properties of EMT and its applications in the field of regenerative medicine.
Abstract: National Science Foundation (U.S.). Graduate Research Fellowship Program (grant number 2388357)

123 citations


Cites methods or result from "Synchronization protocols in distri..."

  • ...Our approach is similar in spirit to prior work [23], [30] that restricts the behavior to reduce anomalies that inherently arise when applying uniprocessor scheduling methods to self-suspending task sets [18], [26]....

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  • ...1) Guiding the Behavior of the Scheduler: Our approach to scheduling tasks bears resemblance to prior art that uses heuristic methods to alter the behavior of self-suspending systems to tightly bound the makespan for the task set [19], [23], [30]....

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Proceedings ArticleDOI
11 Jul 2012
TL;DR: In this paper, the authors proposed techniques to optimize the number of processors needed to schedule hard real-time multi-threaded tasks on multiprocessor platforms with constrained deadlines.
Abstract: These last years, we have witnessed a dramatic increase in the number of cores available in computational platforms. Concurrently, a new coding paradigm dividing tasks into smaller execution instances called threads, was developed to take advantage of the inherent parallelism of multiprocessor platforms. However, only few methods were proposed to efficiently schedule hard real-time multi-threaded tasks on multiprocessor. In this paper, we propose techniques optimizing the number of processors needed to schedule such sporadic parallel tasks with constrained deadlines. We first define an optimization problem determining, for each thread, an intermediate (artificial) deadline minimizing the number of processors needed to schedule the whole task set. The scheduling algorithm can then schedule threads as if they were independent sequential sporadic tasks. The second contribution is an efficient and nevertheless optimal algorithm that can be executed online to determine the thread's deadlines. Hence, it can be used in dynamic systems were all tasks and their characteristics are not known a priori. We finally prove that our techniques achieve a resource augmentation bound of 2 when the threads are scheduled with algorithms such as U-EDF, PD^2, LLREF, DP-Wrap, etc.

92 citations

Patent
Pamela A. Binns1, Aaron Larson1
29 Dec 2000
TL;DR: In this article, slack is stolen from both timeline and reclaimed slack to enable the execution of high priority non-essential tasks on a best efforts basis, and idle time is calculated by priority level.
Abstract: In a multitasking system executing real-time harmonic and dynamic tasks having various priority levels, slack is stolen from both timeline and reclaimed slack to enable the execution of high priority non-essential tasks on a best efforts basis. Counts of the amount of slack consumed, slack reclaimed, and periodic compute time consumed are maintained by individual priority level and dynamically updated at certain times. Idle time is calculated by priority level. Available slack is calculated, and slack is allocated and consumed by rate, with the highest rate first and the lowest rate last. Slack is made available to tasks in more than one time partition. All slack belongs to a common system-wide pool of slack obtained from any one or more of the time partitions. Common slack can also be time-shared by static, non-harmonic tasks residing in different time partitions. Also described are a computer system and various methods that perform slack scheduling in a time-partitioned system.

85 citations

Journal ArticleDOI
TL;DR: Both control-theoretic analysis and simulations show that DEUCON can provide robust utilization guarantees and maintain global system stability despite severe variations in task execution times.
Abstract: Many real-time systems must control their CPU utilizations in order to meet end-to-end deadlines and prevent overload. Utilization control is particularly challenging in distributed real-time systems with highly unpredictable workloads and a large number of end-to-end tasks and processors. This paper presents the decentralized end-to-end utilization control (DEUCON) algorithm, which can dynamically enforce the desired utilizations on multiple processors in such systems. In contrast to centralized control schemes adopted in earlier works, DEUCON features a novel decentralized control structure that requires only localized coordination among neighbor processors. DEUCON is systematically designed based on advances in distributed model predictive control theory. Both control-theoretic analysis and simulations show that DEUCON can provide robust utilization guarantees and maintain global system stability despite severe variations in task execution times. Furthermore, DEUCON can effectively distribute the computation and communication cost to different processors and tolerate considerable communication delay between local controllers. Our results indicate that DEUCON can provide a scalable and robust utilization control for large-scale distributed real-time systems executing in unpredictable environments.

82 citations


Cites background or methods from "Synchronization protocols in distri..."

  • ...If a nongreedy synchronization protocol is used (for example, release guard [33]), every subtask is released periodically without jitter....

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  • ...Traditional approaches for handling end-to-end tasks such as end-to-end scheduling [33] and distributed priority ceiling [27] rely on schedulability analysis, which requires a priori knowledge of worst-case execution times....

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  • ...In an end-to-end scheduling approach [33], the deadline of an end-to-end task is divided into subdeadlines of its subtasks [14], [26]....

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References
More filters
Journal ArticleDOI
TL;DR: The problem of multiprogram scheduling on a single processor is studied from the viewpoint of the characteristics peculiar to the program functions that need guaranteed service and it is shown that an optimum fixed priority scheduler possesses an upper bound to processor utilization.
Abstract: The problem of multiprogram scheduling on a single processor is studied from the viewpoint of the characteristics peculiar to the program functions that need guaranteed service. It is shown that an optimum fixed priority scheduler possesses an upper bound to processor utilization which may be as low as 70 percent for large task sets. It is also shown that full processor utilization can be achieved by dynamically assigning priorities on the basis of their current deadlines. A combination of these two scheduling techniques is also discussed.

7,067 citations

Book
03 Jan 1989
TL;DR: In this paper, the problem of multiprogram scheduling on a single processor is studied from the viewpoint of the characteristics peculiar to the program functions that need guaranteed service, and it is shown that an optimum fixed priority scheduler possesses an upper bound to processor utilization which may be as low as 70 percent for large task sets.
Abstract: The problem of multiprogram scheduling on a single processor is studied from the viewpoint of the characteristics peculiar to the program functions that need guaranteed service. It is shown that an optimum fixed priority scheduler possesses an upper bound to processor utilization which may be as low as 70 percent for large task sets. It is also shown that full processor utilization can be achieved by dynamically assigning priorities on the basis of their current deadlines. A combination of these two scheduling techniques is also discussed.

5,397 citations

Proceedings ArticleDOI
05 Dec 1989
TL;DR: An exact characterization of the ability of the rate monotonic scheduling algorithm to meet the deadlines of a periodic task set and a stochastic analysis which gives the probability distribution of the breakdown utilization of randomly generated task sets are represented.
Abstract: An exact characterization of the ability of the rate monotonic scheduling algorithm to meet the deadlines of a periodic task set is represented. In addition, a stochastic analysis which gives the probability distribution of the breakdown utilization of randomly generated task sets is presented. It is shown that as the task set size increases, the task computation times become of little importance, and the breakdown utilization converges to a constant determined by the task periods. For uniformly distributed tasks, a breakdown utilization of 88% is a reasonable characterization. A case is shown in which the average-case breakdown utilization reaches the worst-case lower bound of C.L. Liu and J.W. Layland (1973). >

1,582 citations


"Synchronization protocols in distri..." refers methods in this paper

  • ...technique, which was first proposed by Lehoczky [ 16 , 2] and later extended by Audsley [3], Tindell [17, 18], and Burns [19],...

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Journal ArticleDOI
TL;DR: It is shown that the problem is NP-hard in all but one special case and the complexity of optimal fixed-priority scheduling algorithm is discussed.

1,230 citations


"Synchronization protocols in distri..." refers background in this paper

  • ...A great deal of work has been done on how to assign the priorities [1, 5, 6] and how to bound the response times of tasks [1, 7, 2] for single processor systems....

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Journal ArticleDOI

1,203 citations


"Synchronization protocols in distri..." refers background in this paper

  • ...A great deal of work has been done on how to assign the priorities [1, 5, 6] and how to bound the response times of tasks [1, 7 , 2] for single processor systems....

    [...]