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An optimal realtime scheduling algorithm for multiprocessors
 In Proc. 27th IEEE International RealTime Systems Symposium, Rio de Janeiro
, 2006
"... Abstract — We consider several object sharing synchronization mechanisms including lockbased, lockfree, and waitfree sharing for LNREF [1], an optimal realtime scheduling algorithm on multiprocessors. We derive LNREF’s minimumrequired space cost for waitfree synchronization using the spaceopt ..."
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Cited by 67 (0 self)
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Abstract — We consider several object sharing synchronization mechanisms including lockbased, lockfree, and waitfree sharing for LNREF [1], an optimal realtime scheduling algorithm on multiprocessors. We derive LNREF’s minimumrequired space cost for waitfree synchronization using the spaceoptimal waitfree algorithm. We then establish the feasibility conditions for lockfree and lockbased sharing under LNREF, and the concomitant tradeoffs. While the tradeoff between waitfree versus the other sharing is obvious, i.e., space and time costs, we show that the tradeoff between lockfree and lockbased sharing for LNREF hinges on the cost of the lockfree retry, blocking time under lockbased. Finally, we numerically evaluate lockfree and lockbased sharing for LNREF. I.
Tardiness bounds under global edf scheduling on a multiprocessor
 In RTSS ’05: Proceedings of the 26th IEEE International RealTime Systems Symposium
, 2005
"... This paper considers the scheduling of soft realtime sporadic task systems under global EDF on an identical multiprocessor. Though Pfair scheduling is theoretically optimal for hard realtime task systems on multiprocessors, it can incur signicant runtime 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 realtime sporadic task systems under global EDF on an identical multiprocessor. Though Pfair scheduling is theoretically optimal for hard realtime task systems on multiprocessors, it can incur signicant runtime 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 realtime systems, where, to ensure that all deadlines are met, approximately 50 % of the available processing capacity will have to be sacriced in the worst case. This may be overkill for soft realtime systems that can tolerate deadline misses by bounded amounts (i.e., bounded tardiness). In this paper, we derive tardiness bounds under preemptive and nonpreemptive global EDF on multiprocessors when the total utilization of a task system is not restricted and may equal the number of processors. Our tardiness bounds depend on pertask 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 multiprocessorbased soft realtime 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.
Efficient synchronization under global EDF scheduling on multiprocessors
 In proceedings of the Euromicro conference on RealTime Systems
, 2006
"... We consider coordinating accesses to shared data structures in multiprocessor realtime systems scheduled under preemptive global EDF. To our knowledge, prior work on global EDF has focused only on systems of independent tasks. We take an initial step here towards a generic resourcesharing framewor ..."
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Cited by 31 (10 self)
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We consider coordinating accesses to shared data structures in multiprocessor realtime systems scheduled under preemptive global EDF. To our knowledge, prior work on global EDF has focused only on systems of independent tasks. We take an initial step here towards a generic resourcesharing framework by considering simple shared objects, such as queues, stacks, and linked lists. In many applications, the predominate use of synchronization constructs is for sharing such simple objects. We analyze two synchronization methods for such objects, one based on queuebased spin locks and a second based on lockfree algorithms. 1
Efficient realtime scheduling algorithms for multiprocessor systems
 IEICE Trans. Communications
, 2002
"... We present an optimal realtime scheduling algorithm for multiprocessors — one that satisfies all task deadlines, when the total utilization demand does not exceed the utilization capacity of the processors. The algorithm called LLREF, is designed based on a novel abstraction for reasoning about tas ..."
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Cited by 29 (0 self)
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We present an optimal realtime scheduling algorithm for multiprocessors — one that satisfies all task deadlines, when the total utilization demand does not exceed the utilization capacity of the processors. The algorithm called LLREF, is designed based on a novel abstraction for reasoning about task execution behavior on multiprocessors: the Time and Local Execution Time Domain Plane (or TL plane). LLREF is based on the fluid scheduling model and the fairness notion, and uses the TL plane to describe fluid schedules without using time quanta, unlike the optimal Pfair algorithm (which uses time quanta). We show that scheduling for multiprocessors can be viewed as repeatedly occurring TL planes, and feasibly scheduling on a single TL plane results in the optimal schedule. We analytically establish the optimality of LLREF. Further, we establish that the algorithm has bounded overhead, and this bound is independent of time quanta (unlike Pfair). Our simulation results validate our analysis on the algorithm overhead.
On multiprocessor utility accrual realtime scheduling with statistical timing assurances
 In IFIP Embedded and Ubiquitous Computing (EUC
, 2006
"... We present the first Utility Accrual (or UA) realtime scheduling algorithm for multiprocessors, called gMUA. The algorithm considers an application model where realtime activities are subject to time/utility function time constraints, variable execution time demands, and resource overloads where t ..."
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Cited by 9 (1 self)
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We present the first Utility Accrual (or UA) realtime scheduling algorithm for multiprocessors, called gMUA. The algorithm considers an application model where realtime activities are subject to time/utility function time constraints, variable execution time demands, and resource overloads where the total activity utilization demand exceeds the total capacity of all processors. We consider the scheduling objective of (1) probabilistically satisfying lower bounds on each activity’s maximum utility and (2) maximizing the systemwide, total accrued utility. We establish several properties of gMUA including optimal total utility (for a special case), conditions under which individual activity utility lower bounds are satisfied, a lower bound on systemwide total accrued utility, and bounded sensitivity for assurances to variations in execution time demand estimates. Our simulation experiments validate our analytical results and confirm the algorithm’s effectiveness and superiority.
Flexible tardiness bounds for sporadic realtime task systems on multiprocessors (extended version). Available at http://www.cs.unc.edu/˜anderson/papers.html
, 2005
"... The earliestdeadlinefirst (EDF) scheduling of a sporadic realtime task system on a multiprocessor may require that the total utilization of the task system, Usum, not exceed (m +1)/2on m processors if every deadline needs to be met. In recent work, we considered the alleviation of this underutili ..."
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Cited by 7 (5 self)
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The earliestdeadlinefirst (EDF) scheduling of a sporadic realtime task system on a multiprocessor may require that the total utilization of the task system, Usum, not exceed (m +1)/2on m processors if every deadline needs to be met. In recent work, we considered the alleviation of this underutilization for task systems that can tolerate deadline misses by bounded amounts (i.e., bounded tardiness). We showed that if Usum ≤ m and tasks are not pinned to processors, then the tardiness of each task is bounded under both preemptive and nonpreemptive EDF. However, the tardiness bounds derived are applicable to every task in the task system, i.e., any task may incur maximum tardiness. In this paper, we consider supporting tasks whose tolerances to tardiness are less than that known to be possible under EDF. We propose a new scheduling policy, called EDFhl, which is a variant of EDF, and show that under EDFhl, any tardiness, including zero tardiness, can be ensured for a limited number of privileged tasks, and that bounded tardiness can be guaranteed to the remaining tasks if their utilizations are restricted. EDFhl reduces to EDF in the absence of privileged tasks. The tardiness bound that we derive is a function of Usum, in addition to individual task parameters. Hence, tardiness for all tasks can be lowered by lowering Usum. A simulationbased evaluation of the tardiness bounds that are possible is provided. 1
Utility Accrual RealTime Scheduling and Synchronization on Single and Multiprocessors: Models, Algorithms, and Tradeoffs
, 2006
"... This dissertation presents a class of utility accrual scheduling and synchronization algorithms for dynamic, single and multiprocessor realtime systems. Dynamic realtime systems operate in environments with runtime uncertainties including those on activity execution times and arrival behaviors. ..."
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This dissertation presents a class of utility accrual scheduling and synchronization algorithms for dynamic, single and multiprocessor realtime systems. Dynamic realtime systems operate in environments with runtime uncertainties including those on activity execution times and arrival behaviors. We consider the time/utility function (or TUF) timing model for specifying application time constraints, and the utility accrual (or UA) timeliness optimality criteria of satisfying lower bounds on accrued activity utility, and maximizing the total accrued utility. Efficient TUF/UA scheduling algorithms exist for single processors—e.g., the Resourceconstrained Utility Accrual scheduling algorithm (RUA), and the Dependent Activity Scheduling Algorithm (DASA). However, they all use lockbased synchronization. To overcome shortcomings of lockbased (e.g., serialized object access, increased runtime overhead, deadlocks), we consider nonblocking synchronization including waitfree and lockfree synchronization. We present a bufferoptimal, schedulerindependent waitfree synchronization protocol (the first such), and develop waitfree versions of RUA and DASA. We also develop their lockfree versions, and upper bound their retries under the unimodal arbitrary arrival model. The tradeoff between waitfree, lockfree, and lockbased is fundamentally about their space and
A Variant of FPZL Algorithm
"... Fixed priority until Zero Laxity (FPZL) algorithm is the minimally dynamic scheduling algorithm. In FPZL, fixed priorities are assigned to the jobs and are scheduled accordingly until the state of zero laxity is reached and it does not follow any priority order. FPZL concentrates on scheduling more ..."
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Fixed priority until Zero Laxity (FPZL) algorithm is the minimally dynamic scheduling algorithm. In FPZL, fixed priorities are assigned to the jobs and are scheduled accordingly until the state of zero laxity is reached and it does not follow any priority order. FPZL concentrates on scheduling more jobs as far as possible. The algorithm which is proposed in this paper is the variant of FPZL which employs the priority order. Instead of giving up processing of some tasks completely, this algorithm completes some portion of the tasks and at the same time if any zero laxity task arrives it takes that task also into consideration and schedules accordingly. In this way, this algorithm tries to process more jobs as compared to the FPZL algorithm and increases the CPU Utilization.