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Implications of Classical Scheduling Results For RealTime Systems
 IEEE COMPUTER
, 1995
"... Important classical scheduling theory results for realtime computing are identified. Implications of these results from the perspective of a realtime systems designer are discussed. Uniprocessor and multiprocessor results are addressed as well as important issues such as future release times, pre ..."
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Cited by 121 (1 self)
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Important classical scheduling theory results for realtime computing are identified. Implications of these results from the perspective of a realtime systems designer are discussed. Uniprocessor and multiprocessor results are addressed as well as important issues such as future release times, precedence constraints, shared resources, task value, overloads, static versus dynamic scheduling, preemption versus nonpreemption, multiprocessing anomalies, and metrics. Examples of what scheduling algorithms are used in actual applications are given.
NonClairvoyant Scheduling
, 1993
"... Virtually all research in scheduling theory has been concerned with clairvoyant scheduling where it is assumed that the characteristics of a job (in particular, its execution time, release time and dependence on other jobs) are known a priori. This assumption is invalid for scheduling problems t ..."
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Cited by 87 (7 self)
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Virtually all research in scheduling theory has been concerned with clairvoyant scheduling where it is assumed that the characteristics of a job (in particular, its execution time, release time and dependence on other jobs) are known a priori. This assumption is invalid for scheduling problems that arise in timesharing operating systems where the scheduler must provide fast turnaround for processes being generated by the users without any knowledge of the future behavior of these processes. We study preemptive, nonclairvoyant scheduling schemes where the scheduler has no knowledge of the jobs' characteristics. We develop a model for evaluating scheduling strategies for single and multiprocessor systems. This model compares the nonclairvoyant scheduler against the optimal clairvoyant scheduler, and it takes into account various issues such as release times, execution time, preemption cost, and the interdependence between jobs. Within this model we study some standard sc...
Models of Machines and Computation for Mapping in Multicomputers
, 1993
"... It is now more than a quarter of a century since researchers started publishing papers on mapping strategies for distributing computation across the computation resource of multiprocessor systems. There exists a large body of literature on the subject, but there is no commonlyaccepted framework ..."
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Cited by 79 (1 self)
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It is now more than a quarter of a century since researchers started publishing papers on mapping strategies for distributing computation across the computation resource of multiprocessor systems. There exists a large body of literature on the subject, but there is no commonlyaccepted framework whereby results in the field can be compared. Nor is it always easy to assess the relevance of a new result to a particular problem. Furthermore, changes in parallel computing technology have made some of the earlier work of less relevance to current multiprocessor systems. Versions of the mapping problem are classified, and research in the field is considered in terms of its relevance to the problem of programming currently available hardware in the form of a distributed memory multiple instruction stream multiple data stream computer: a multicomputer.
EndtoEnd Scheduling to Meet Deadlines in Distributed Systems
, 1994
"... In a distributed system or communication network tasks may need to be executed on more than one processor. For timecritical tasks, the timing constraints are typically given as endtoend releasetimes and deadlines. This paper describes algorithms to schedule a class of systems where all the tasks ..."
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Cited by 68 (3 self)
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In a distributed system or communication network tasks may need to be executed on more than one processor. For timecritical tasks, the timing constraints are typically given as endtoend releasetimes and deadlines. This paper describes algorithms to schedule a class of systems where all the tasks execute on different processors in turn in the same order. This endtoend scheduling problem is known as the flowshop problem. We present two cases where the problem is tractable and evaluate a heuristic for the N Phard general case. We generalize the traditional flowshop model in two directions. First, we present an algorithm for scheduling flow shops where tasks can be serviced more than once by some processors. Second, we describe a heuristic algorithm to schedule flow shops that consist of periodic tasks. Some considerations are made about scheduling systems with more than one flow shop. 1
Scheduling Algorithms
, 1997
"... Introduction Scheduling theory is concerned with the optimal allocation of scarce resources to activities over time. The practice of this field dates to the first time two humans contended for a shared resource and developed a plan to share it without bloodshed. The theory of the design of algorith ..."
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Cited by 64 (1 self)
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Introduction Scheduling theory is concerned with the optimal allocation of scarce resources to activities over time. The practice of this field dates to the first time two humans contended for a shared resource and developed a plan to share it without bloodshed. The theory of the design of algorithms for scheduling is younger, but still has a significant historythe earliest papers in the field were published more than forty years ago. Scheduling problems arise in a variety of settings, as is illustrated by the following examples: Example 1: Consider the central processing unit of a computer that must process a sequence of jobs that arrive over time. In what order should the jobs be processed in order to minimize, on average, the time that a job is in the system from arrival to completion? Example 2: Consider a team of five astronauts preparing for the reentry of their space shuttle into the at
Approximation Schemes for Minimizing Average Weighted Completion Time with Release Dates
 IN PROCEEDINGS OF THE 40TH ANNUAL IEEE SYMPOSIUM ON FOUNDATIONS OF COMPUTER SCIENCE
, 1999
"... We consider the problem of scheduling n jobs with release dates on m machines so as to minimize their average weighted completion time. We present the first known polynomial time approximation schemes for several variants of this problem. Our results include PTASs for the case of identical parallel ..."
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Cited by 58 (16 self)
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We consider the problem of scheduling n jobs with release dates on m machines so as to minimize their average weighted completion time. We present the first known polynomial time approximation schemes for several variants of this problem. Our results include PTASs for the case of identical parallel machines and a constant number of unrelated machines with and without preemption allowed. Our schemes are efficient: for all variants the running time for a (1 + ffl) approximation is of the form f(1=ffl; m)poly(n).
Value vs. Deadline Scheduling in Overload Conditions
 IN PROCEEDINGS OF THE 16TH REALTIME SYSTEMS SYMPOSIUM
, 1995
"... In this paper we present a comparative study among scheduling algorithms which use different priority assignments and different guarantee mechanisms to improve the performance of a realtime system during overload conditions. In order to increase the information available to the system for enhancing ..."
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Cited by 52 (0 self)
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In this paper we present a comparative study among scheduling algorithms which use different priority assignments and different guarantee mechanisms to improve the performance of a realtime system during overload conditions. In order to increase the information available to the system for enhancing the quality of service, we assume that tasks are characterized not only by a deadline, but also by an importance value. The performance of the scheduling algorithm is then evaluated by computing the cumulative value gained on a task set, i.e. the sum of the values of those tasks that completed by their deadline. The purpose of this simulation study was twofold. Firstly, we wanted to discover which priority assignment is able to achieve the best performance in overload conditions. Secondly, we were interested in understanding how the pessimistic assumptions made in the guarantee test affect the performance of the scheduling algorithms, and how much a reclaiming mechanism can compensate this ...
Minimizing Average Completion Time in the Presence of Release Dates
, 1995
"... A natural and basic problem in scheduling theory is to provide good average quality of service to a stream of jobs that arrive over time. In this paper we consider the problem of scheduling n jobs that are released over time in order to minimize the average completion time of the set of jobs. In con ..."
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Cited by 42 (7 self)
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A natural and basic problem in scheduling theory is to provide good average quality of service to a stream of jobs that arrive over time. In this paper we consider the problem of scheduling n jobs that are released over time in order to minimize the average completion time of the set of jobs. In contrast to the problem of minimizing average completion time when all jobs are available at time 0, all the problems that we consider are NPhard, and essentially nothing was known about constructing good approximations in polynomial time. We give the first constantfactor approximation algorithms for several variants of the single and parallel machine model. Many of the algorithms are based on interesting algorithmic and structural relationships between preemptive and nonpreemptive schedules and linear programming relaxations of both. Many of the algorithms generalize to the minimization of average weighted completion time as well. 1 Introduction Two important characteristics of many realw...
Preemptive Multiprocessor Scheduling with Rejection
 Theoretical Computer Science
, 1999
"... The problem of online multiprocessor scheduling with rejection was introduced by Bartal, Leonardi, MarchettiSpaccamela, Sgall and Stougie [4]. They show that for this problem the competitive ratio is 1+ OE ß 2:61803, where OE is the golden ratio. A modified model of multiprocessor scheduling with r ..."
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Cited by 27 (3 self)
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The problem of online multiprocessor scheduling with rejection was introduced by Bartal, Leonardi, MarchettiSpaccamela, Sgall and Stougie [4]. They show that for this problem the competitive ratio is 1+ OE ß 2:61803, where OE is the golden ratio. A modified model of multiprocessor scheduling with rejection is presented where preemption is allowed. For this model, it is shown that better performance is possible. An online algorithm which is (4+ p 10)=3 ! 2:38743competitive is presented. We prove that the competitive ratio of any online algorithm is at least 2.12457. We say that an algorithm schedules obliviously if the accepted jobs are scheduled without knowledge of the rejection penalties. We also show a lower bound of 2.33246 on the competitive ratio of any online algorithm which schedules obliviously. As a subroutine in our algorithm, we use a new optimal online algorithm for preemptive scheduling without rejection. This algorithm never acheives a larger makespan than that of the...
Scheduling Unrelated Machines by Randomized Rounding
 SIAM Journal on Discrete Mathematics
, 1999
"... In this paper, we provide a new class of randomized approximation algorithms for parallel machine scheduling problems. The most general model we consider is scheduling unrelated machines with release dates (or even network scheduling) so as to minimize the average weighted completion time. We introd ..."
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Cited by 24 (3 self)
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In this paper, we provide a new class of randomized approximation algorithms for parallel machine scheduling problems. The most general model we consider is scheduling unrelated machines with release dates (or even network scheduling) so as to minimize the average weighted completion time. We introduce an LP relaxation in timeindexed variables for this problem. The crucial idea to derive approximation results is not to use standard list scheduling, but rather to assign jobs randomly to machines (by interpreting LP solutions as probabilities), and to perform list scheduling on each of them. Our main result is a (2 + e)approximation algorithm for this general model which improves upon performance guarantee 16=3 due to Hall, Shmoys, and Wein. In the absence of nontrivial release dates, we get a (3=2 + e)approximation. At the same time we prove corresponding bounds on the quality of the LP relaxation. A perhaps surprising implication for identical parallel machines is that jobs are ra...