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318
Resource partitioning among real-time applications
- IN PROCEEDINGS OF EUROMICRO CONFERENCE ON REAL-TIME SYSTEMS
, 2003
"... When executing different real-time applications on a single processor system, one problem is how to compose these applications and guarantee at the same time that their timing requirements are not violated. A possible way of composing applications is through the resource reservation approach. Each a ..."
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Cited by 104 (17 self)
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When executing different real-time applications on a single processor system, one problem is how to compose these applications and guarantee at the same time that their timing requirements are not violated. A possible way of composing applications is through the resource reservation approach. Each application is handled by a dedicated server that is assigned a fraction of the processor. Using this approach, the system can be seen as a two-level hierarchical scheduler. A considerable amount of work has been recently addressed to the analysis of this kind of hierarchical systems. However, a question is still unanswered: given a set of real-time tasks to be handled by a server, how to assign the server parameters so that the task set is feasible? In this paper, we answer to the previous question for the case of fixed priority local scheduler by presenting a methodology for computing the class of server parameters that make the task set feasible.
HLS: A framework for composing soft real-time schedulers
- In Proceedings of the 22nd IEEE Real-Time Systems Symposium (RTSS 2001
, 2001
"... Hierarchical CPU scheduling has emerged as a way to (1) support applications with diverse scheduling requirements in open systems, and (2) provide load isolation between applications, users, and other resource principals. Most existing work on hierarchical scheduling has focused on systems that prov ..."
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Cited by 90 (9 self)
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Hierarchical CPU scheduling has emerged as a way to (1) support applications with diverse scheduling requirements in open systems, and (2) provide load isolation between applications, users, and other resource principals. Most existing work on hierarchical scheduling has focused on systems that provide a fixed scheduling model: the schedulers in part or all of the hierarchy are specified in advance. In this paper we describe a system of guarantees that permits a general hierarchy of soft real-time schedulers—one that contains arbitrary scheduling algorithms at all points within the hierarchy—to be analyzed. This analysis results in deterministic guarantees for threads at the leaves of the hierarchy. We also describe the design, implementation, and performance evaluation of a system for supporting such a hierarchy in the Windows 2000 kernel. Finally, we show that complex scheduling behaviors can be created using small schedulers as components and describe the HLS programming environment. 1.
Optimal Rate-based Scheduling on Multiprocessors
- In Proceedings of the 34th ACM Symposium on Theory of Computing
, 2001
"... We consider the intra-sporadic task model, which is a generalization of the sporadic task model motivated by recent work on Pfair scheduling. The intra-sporadic model is essentially a quantum-based, multiprocessor variant of the uniprocessor rate-based execution model of Jeffay and Goddard. In the i ..."
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Cited by 81 (41 self)
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We consider the intra-sporadic task model, which is a generalization of the sporadic task model motivated by recent work on Pfair scheduling. The intra-sporadic model is essentially a quantum-based, multiprocessor variant of the uniprocessor rate-based execution model of Jeffay and Goddard. In the intra-sporadic model, a task is specified by an average rate of execution, and there is no restriction on instantaneous execution rates. Such exibility is useful in applications in which some processing steps may be highly jittered. In previous work, we showed that an intra-sporadic task system is feasible on M processors i its total utilization is at most M . We also gave an optimal algorithm for scheduling intra-sporadic tasks on two processors. In this paper, we show that the PD² Pfair algorithm can be used to schedule any intra-sporadic task system that is feasible on M processors. Because the sporadic model is a special case of the intrasporadic model, our work shows that PD² is also optimal for scheduling sporadic tasks on a multiprocessor. This paper is the first to show that sporadic or intra-sporadic tasks can be optimally scheduled on systems of more than two processors.
Analysis of a reservation-based feedback scheduler
- in IEEE RTSS
, 2002
"... When executing soft real-time tasks in a shared processor, it is important to properly allocate the computational resources such that the quality of service requirements of each task are satisfied. In this paper we propose Adaptive Reservations, based on applying a feedback scheme to a reservation b ..."
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Cited by 78 (17 self)
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When executing soft real-time tasks in a shared processor, it is important to properly allocate the computational resources such that the quality of service requirements of each task are satisfied. In this paper we propose Adaptive Reservations, based on applying a feedback scheme to a reservation based scheduler. After providing a precise mathematical model of the scheduler, we describe how this model can be used for synthesising the controller by applying results from control theory. Finally, we show the effectiveness of our method by simulation and by experiments with an MPEG player running on a modified Linux kernel. 1.
Capacity Sharing for Overrun Control
- IEEE Real-Time Systems Symposium
, 2000
"... In this paper, we present a general scheduling methodology for managing overruns in a real-time environment, where tasks may have different criticality and flexible timing constraints. The proposed method achieves isolation among tasks through a resource reservation mechanism which bounds the effect ..."
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Cited by 65 (8 self)
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In this paper, we present a general scheduling methodology for managing overruns in a real-time environment, where tasks may have different criticality and flexible timing constraints. The proposed method achieves isolation among tasks through a resource reservation mechanism which bounds the effects of task interference, but also performs efficient reclaiming of the unused computation times to relax the utilization constraints imposed by isolation. The enhancements achieved by the proposed approach resulted to be very effective with respect to classical reservation schemes. The performance has been evaluated by implementing the algorithm on a real-time kernel. The runtime overhead introduced by the scheduling mechanism has also been investigated with specific experiments, in order to be taken into account in the schedulability analysis. However, it resulted to be negligible in most practical cases.
Tardiness bounds under global edf scheduling on a multiprocessor
- In RTSS ’05: Proceedings of the 26th IEEE International Real-Time Systems Symposium
, 2005
"... This paper considers the scheduling of soft real-time sporadic task systems under global EDF on an iden-tical multiprocessor. Though Pfair scheduling is theoretically optimal for hard real-time task systems on multiprocessors, it can incur signicant run-time overhead. Hence, other scheduling algorit ..."
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Cited by 63 (37 self)
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This paper considers the scheduling of soft real-time sporadic task systems under global EDF on an iden-tical multiprocessor. Though Pfair scheduling is theoretically optimal for hard real-time task systems on multiprocessors, it can incur signicant run-time overhead. Hence, other scheduling algorithms that are not optimal, including EDF, have continued to receive considerable attention. However, prior research on such algorithms has focussed mostly on hard real-time systems, where, to ensure that all deadlines are met, ap-proximately 50 % of the available processing capacity will have to be sacriced in the worst case. This may be overkill for soft real-time systems that can tolerate deadline misses by bounded amounts (i.e., bounded tardiness). In this paper, we derive tardiness bounds under preemptive and non-preemptive global EDF on multiprocessors when the total utilization of a task system is not restricted and may equal the number of pro-cessors. Our tardiness bounds depend on per-task utilizations and execution costs the lower these values, the lower the tardiness bounds. As a nal remark, we note that global EDF may be superior to partitioned EDF for multiprocessor-based soft real-time systems in that the latter does not offer any scope to improve system utilization even if bounded tardiness can be tolerated. ¤Work supported by NSF grants CCR 0204312, CCR 0309825, and CCR 0408996. The rst author was also supported by an IBM Ph.D. fellowship.
Improving soft real-time performance through better slack reclaiming
- IN PROC. OF REAL-TIME SYSTEMS SYMPOSIUM (RTSS
, 2005
"... Modern operating systems frequently support applications with a variety of timing constraints including hard real-time, soft real-time, and best-effort. To guarantee performance, critical applications typically over-reserve resources based on worst-case resource usage estimates, while others may res ..."
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Cited by 51 (3 self)
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Modern operating systems frequently support applications with a variety of timing constraints including hard real-time, soft real-time, and best-effort. To guarantee performance, critical applications typically over-reserve resources based on worst-case resource usage estimates, while others may reserve based on average-case or other estimates. When resources are fully subscribed, the performance of soft- and non-real-time applications depends upon the effective distribution of dynamic slack—reserved, but unused resources—from other tasks. Motivated by several representative examples, we derive four general principles for the effective management of slack. We have implemented these principles in four progressively better slack schedulers that demonstrate their effectiveness. BACKSLASH, which employs all four principles, misses fewer soft realtime deadlines than all of the other slack schedulers we examined.
Rate Monotonic vs. EDF: Judgment Day
, 2005
"... Since the first results published in 1973 by Liu and Layland on the Rate Monotonic (RM) and Earliest Deadline First (EDF) algorithms, a lot of progress has been made in the schedulability analysis of periodic task sets. Unfortunately, many misconceptions still exist about the properties of these two ..."
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Cited by 51 (3 self)
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Since the first results published in 1973 by Liu and Layland on the Rate Monotonic (RM) and Earliest Deadline First (EDF) algorithms, a lot of progress has been made in the schedulability analysis of periodic task sets. Unfortunately, many misconceptions still exist about the properties of these two scheduling methods, which usually tend to favor RM more than EDF. Typical wrong statements often heard in technical conferences and even in research papers claim that RM is easier to analyze than EDF, it introduces less runtime overhead, it is more predictable in overload conditions, and causes less jitter in task execution. Since the above statements are either wrong, or not precise, it is time to clarify these issues in a systematic fashion, because the use of EDF allows a better exploitation of the available resources and significantly improves system’s performance. This paper compares RM against EDF under several aspects, using existing theoretical results, specific simulation experiments, or simple counterexamples to show that many common beliefs are either false or only restricted to specific situations.
Implementing a General Real-Time Scheduling Framework in the RED-Linux Real-Time Kernel
- in IEEE Real-Time Systems Symposium
, 1999
"... Many scheduling paradigms have been studied for realtime applications and real-time communication network. Among them, the most commonly used paradigms include priority-driven, time-driven and share-driven paradigms. In this paper, we present a general scheduling framework which is designed to integ ..."
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Cited by 49 (1 self)
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Many scheduling paradigms have been studied for realtime applications and real-time communication network. Among them, the most commonly used paradigms include priority-driven, time-driven and share-driven paradigms. In this paper, we present a general scheduling framework which is designed to integrate these paradigms in one framework. The framework is implemented in our real-time extension of the Linux kernel, RED-Linux. Two scheduler components are used in the framework: Allocator and Dispatcher. For each job, the framework identifies four scheduling attributes: priority, start_time, finish_time and budget. We show that the framework can be used to efficiently implement many well-known scheduling algorithms. We also measure and analyze the performance of the framework implemented in RED-Linux. 1
