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63
Quickrelease Fair Scheduling
 In Proceedings of the 12th Euromicro Conference on RealTime Systems
, 2003
"... In prior work on multiprocessor fairness, efficient techniques with provable properties for reallocating spare processing capacity have been elusive. In this paper, we address this shortcoming by proposing a new notion of multiprocessor fairness, called quickrelease fair (QRfair) scheduling, which ..."
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Cited by 95 (36 self)
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In prior work on multiprocessor fairness, efficient techniques with provable properties for reallocating spare processing capacity have been elusive. In this paper, we address this shortcoming by proposing a new notion of multiprocessor fairness, called quickrelease fair (QRfair) scheduling, which is a derivative of Pfair scheduling that allows efficient allocation of spare capacity. Under QRfair scheduling, each task is specified by giving both a minimum and a maximum weight (i.e., processor share). The goal is to schedule each task (as the available spare capacity changes) at a rate that is (i) at least that implied by its minimum weight and (ii) at most that implied by its maximum weight. Our contributions are fourfold. First, we present a quickrelease variant of the PD Pfair scheduling algorithm called PD . Second, we formally prove that the allocations of PD always satisfy (i) and (ii). Third, we consider the problem of defining maximum weights in a way that encourages a fair distribution of spare capacity. Fourth, we present results from extensive simulation experiments that show the efficacy of PD in allocating spare capacity.
Optimal Ratebased Scheduling on Multiprocessors
 In Proceedings of the 34th ACM Symposium on Theory of Computing
, 2001
"... We consider the intrasporadic task model, which is a generalization of the sporadic task model motivated by recent work on Pfair scheduling. The intrasporadic model is essentially a quantumbased, multiprocessor variant of the uniprocessor ratebased execution model of Jeffay and Goddard. In the i ..."
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Cited by 83 (41 self)
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We consider the intrasporadic task model, which is a generalization of the sporadic task model motivated by recent work on Pfair scheduling. The intrasporadic model is essentially a quantumbased, multiprocessor variant of the uniprocessor ratebased execution model of Jeffay and Goddard. In the intrasporadic 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 intrasporadic task system is feasible on M processors i its total utilization is at most M . We also gave an optimal algorithm for scheduling intrasporadic tasks on two processors. In this paper, we show that the PD&sup2; Pfair algorithm can be used to schedule any intrasporadic task system that is feasible on M processors. Because the sporadic model is a special case of the intrasporadic model, our work shows that PD&sup2; is also optimal for scheduling sporadic tasks on a multiprocessor. This paper is the first to show that sporadic or intrasporadic tasks can be optimally scheduled on systems of more than two processors.
Vsched: Mixing batch and interactive virtual machines using periodic realtime scheduling
 In Proceedings of ACM/IEEE SC 2005 (Supercomputing
, 2005
"... We are developing Virtuoso, a system for distributed computing using virtual machines (VMs). Virtuoso must be able to mix batch and interactive VMs on the same physical hardware, while satisfying constraints on responsiveness and compute rates for each workload. VSched is the component of Virtuoso t ..."
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Cited by 55 (15 self)
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We are developing Virtuoso, a system for distributed computing using virtual machines (VMs). Virtuoso must be able to mix batch and interactive VMs on the same physical hardware, while satisfying constraints on responsiveness and compute rates for each workload. VSched is the component of Virtuoso that provides this capability. VSched is an entirely userlevel tool that interacts with the stock Linux kernel running below any typeII virtual machine monitor to schedule all VMs (indeed, any process) using a periodic realtime scheduling model. This abstraction allows compute rate and responsiveness constraints to be straightforwardly described using a period and a slice within the period, and it allows for fast and simple admission control. This paper makes the case for periodic realtime scheduling for VMbased computing environments, and then describes and evaluates VSched. It also applies VSched to scheduling parallel workloads, showing that it can help a BSP application maintain a fixed stable performance despite externally caused load imbalance.
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 50 (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.
Efficient scheduling of soft realtime applications on multiprocessors
 In Proceedings of the 15th Euromicro Conference on Realtime Systems
, 2003
"... In soft realtime applications, tasks are allowed to miss their deadlines. Thus, lesscostly scheduling algorithms can be used at the price of occasional violations of timing constraints. This may be acceptable if reasonable tardiness bounds (i.e., bounds on the extent to which deadlines may be miss ..."
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Cited by 43 (20 self)
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In soft realtime applications, tasks are allowed to miss their deadlines. Thus, lesscostly scheduling algorithms can be used at the price of occasional violations of timing constraints. This may be acceptable if reasonable tardiness bounds (i.e., bounds on the extent to which deadlines may be missed) can be guaranteed. In this paper, we consider soft realtime applications implemented on multiprocessors. Pfair scheduling algorithms are the only known means of optimally scheduling hard realtime applications on multiprocessors. For this reason, we consider the use of such algorithms here. In the design of Pfair scheduling algorithms, devising schemes to correctly break ties when several tasks have the same deadline is a critical issue. Such tiebreaking schemes entail overhead that may be unacceptable or unnecessary in soft realtime applications. In this paper, we consider the earliest pseudodeadline first (EPDF) Pfair algorithm, which avoids this overhead by using no tiebreaking information. Our main contributions are twofold. First, we establish a condition for ensuring a tardiness of at most one quantum under EPDF. This condition is very liberal and should often hold in practice. Second, we present simulation results involving randomlygenerated task sets, including those that do not satisfy our condition. In these experiments, deadline misses rarely occurred, and no misses by more than one quantum ever occurred. ∗ Work supported by NSF grants CCR 9972211, CCR 9988327, ITR 0082866, and CCR 0204312. 1
The Case for Fair Multiprocessor Scheduling
 In Proceedings of the 11th International Workshop on Parallel and Distributed Realtime Systems
, 2002
"... Partitioning and global scheduling are two approaches for scheduling realtime tasks on multiprocessors. Though partitioning is suboptimal it has traditionally been preferred; this is mainly due to the fact that wellunderstood uniprocessor scheduling algorithms can be used on each processor. In re ..."
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Cited by 35 (8 self)
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Partitioning and global scheduling are two approaches for scheduling realtime tasks on multiprocessors. Though partitioning is suboptimal it has traditionally been preferred; this is mainly due to the fact that wellunderstood uniprocessor scheduling algorithms can be used on each processor. In recent years, global scheduling algorithms based on the concept of "proportionate fairness" (Pfairness)have received considerabl attention. Pfairal)[[2#3) are of interest because they are currentl the onl known method for optimal) schedul13 periodic, sporadic, and "ratebased" task systems on mul6[]2 cessors. In addition, there has been growing practical interest in schedul32 with fairness guarantees. However, the frequency of context switching and migration in Pfairscheduls systems has l) to some questions concerning the practicalR y of Pfair schedul#6) In this paper, we investigate this issue by comparing the PD Pfairalir)2B1 to the EDFFF partitioning scheme, which uses "first fit" (FF)as a partitioning heuristic and theearlBB):[B2B1)l first (EDF)al):R3R# for perprocessor schedul1): We present experimental resul) that show that is competitive with, and in some cases outperforms, EDFFF. These resulL suggest that Pfair schedulR) is aviabl all1):R] e to partitioning. Furthermore, as discussed herein, Pfair scheduling provides many additional benefits, such assimpl and efficient synchronization, temporal isolL1]): faul tol1]):R6 and support for dynamic tasks.
Scheduling of Dynamic Task Systems on Multiprocessors
 In Proceedings of the International Workshop on Parallel and Distributed RealTime Systems
, 2003
"... In dynamic realtime task systems, tasks that are subject to deadlines are allowed to join and leave the system. In previous work, Stoica et al. and Baruah et al. presented conditions under which such joins and leaves may occur in fairscheduled uniprocessor systems without causing missed deadlines. ..."
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Cited by 32 (17 self)
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In dynamic realtime task systems, tasks that are subject to deadlines are allowed to join and leave the system. In previous work, Stoica et al. and Baruah et al. presented conditions under which such joins and leaves may occur in fairscheduled uniprocessor systems without causing missed deadlines. In this paper, we extend their work by considering fairscheduled multiprocessors. We show that their conditions are sufficient on M processors, under any deadlinebased Pfair scheduling algorithm, if the utilization of every subset of M − 1 tasks is at most one. Further, for the general case in which task utilizations are not restricted in this way, we derive sufficient join/leave conditions for the PD 2 Pfair algorithm. We also show that, in general, these conditions cannot be improved upon without causing missed deadlines.
On the Implementation of Pfairscheduled Multiprocessor Systems
, 2004
"... The goal of this dissertation is to extend the Pfair scheduling approach in order to enable its efficient implementation on a realtime multiprocessor. At present, Pfair scheduling is the only known means for optimally scheduling recurrent realtime tasks on multiprocessors. In
addition, there has b ..."
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Cited by 30 (12 self)
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The goal of this dissertation is to extend the Pfair scheduling approach in order to enable its efficient implementation on a realtime multiprocessor. At present, Pfair scheduling is the only known means for optimally scheduling recurrent realtime tasks on multiprocessors. In
addition, there has been growing practical interest in such approaches due to their fairness
guarantees. Unfortunately, prior work in this area has considered only the scheduling of
independent tasks, which do not communicate with each other or share resources. The work
presented herein focuses both on adding support for these actions and also on developing
techniques for reducing various forms of implementation overhead, including that produced
by task migrations and context switches. The thesis of this dissertation is:
tasks can be efficiently synchronized in Pfairscheduled systems and overhead due
to common system events, such as context switches and migrations, can be reduced.
This thesis is established through research in three areas. First, the preexisting Pfair schedul
ing theory is extended to support the scheduling of groups of tasks as a single entity. Second,
mechanisms for supporting both lockbased and lockfree synchronization are presented. Lock
based synchronization coordinates access to shared resources through the use of semaphores.
On the other hand, lockfree operations are optimistically attempted and then retried if the
operation fails. Last, the deployment of Pfair scheduling on a symmetric multiprocessor is
considered.
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 28 (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.
Efficient and Flexible Fair Scheduling of Realtime Tasks on Multiprocessors
 University
, 2003
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