Results 1  10
of
17
A Parametrized BranchandBound Strategy for Scheduling PrecedenceConstrained Tasks on a Multiprocessor System
 Proc. of the Int'l Conf. on Parallel Processing
, 1997
"... In this paper we experimentally evaluate the performance of a parametrized branchandbound (B&B) algorithm for scheduling realtime tasks on a multiprocessor system. The objective of the B&B algorithm is to minimize the maximum task lateness in the system. We show that a lastinfirstout (LIFO) ve ..."
Abstract

Cited by 20 (7 self)
 Add to MetaCart
In this paper we experimentally evaluate the performance of a parametrized branchandbound (B&B) algorithm for scheduling realtime tasks on a multiprocessor system. The objective of the B&B algorithm is to minimize the maximum task lateness in the system. We show that a lastinfirstout (LIFO) vertex selection rule clearly outperforms the commonly used leastlowerbound (LLB) rule for the scheduling problem. We also present a new adaptive lowerbound cost function that greatly improves the performance of the B&B algorithm when parallelism in the application cannot be fully exploited on the multiprocessor architecture. Finally, we evaluate a set of heuristic strategies, one of which generates nearoptimal results with performance guarantees and another of which generates approximate results without performance guarantees. 1 Introduction Since its introduction in the field of artificial intelligence, the branchandbound (B&B) strategy has been successfully used for finding optimal ...
Identical Parallel Machines Vs UnitTime Shops And Preemptions Vs Chains In Scheduling Complexity
 European Journal of Operational Research
, 2000
"... . This paper surveys, analyses and establishes new polynomialtime reductions among scheduling problems that connect identical parallel machines with unittime shops and the preemption facility with chainlike precedence constraints in equal machine environments. The reductions turn out to be une ..."
Abstract

Cited by 14 (7 self)
 Add to MetaCart
. This paper surveys, analyses and establishes new polynomialtime reductions among scheduling problems that connect identical parallel machines with unittime shops and the preemption facility with chainlike precedence constraints in equal machine environments. The reductions turn out to be unexpectedly fruitful in clarifying the complexity status of many scheduling problems that were open before. New complexity results in the paper are devoted to identical parallel machines, ow shops and open shops. 1. Introduction Recently found mass polynomialtime reductions between scheduling problems on identical parallel machines and shop scheduling problems with nonpreemptive unit processing time operations proved to be very eective in studying their complexity. The latter problems we simply call unittime shops. Reductions of unittime shops to identical parallel machines we call parallelizings, and the inverse reductions, i.e., of identical parallel machines to unittime shops, we c...
Complexity Results for SingleMachine Problems with Positive FinishStart TimeLags
 Computing
, 1998
"... In a singlemachine problem with timelags a set of jobs has to be processed on a single machine in such a way that certain timing restrictions between the finishing and starting times of the jobs are satisfied and a given objective function is minimized. We consider the case of positive finishstart ..."
Abstract

Cited by 12 (0 self)
 Add to MetaCart
In a singlemachine problem with timelags a set of jobs has to be processed on a single machine in such a way that certain timing restrictions between the finishing and starting times of the jobs are satisfied and a given objective function is minimized. We consider the case of positive finishstart timelags l ij which mean that between the finishing time of job i and the starting time of job j the minimal distance l ij has to be respected. New complexity results are derived for singlemachine problems with constant positive timelags l ij = l which also lead to new results for flowshop problems with unit processing times and job precedences. Key words: complexity results, timelags, single machine, flowshop problem Supported by the Deutsche Forschungsgemeinschaft, Project `Komplexe MaschinenSchedulingprobleme ' 1 Introduction In a singlemachine problem a set of jobs j = 1; : : : ; n has to be processed without preemption on a single machine in such a way that at most one jo...
GAST: A Flexible and Extensible Tool for Evaluating Multiprocessor Assignment and Scheduling Techniques
 Proc. of the Int'l Conf. on Parallel Processing
, 1998
"... Automatic tool support for scheduling applications on multiprocessor platforms is of paramount importance both to guarantee critical application demands and to keep development costs down. In this paper, we present GAST, an objectoriented evaluation environment for multiprocessor assignment and sche ..."
Abstract

Cited by 11 (7 self)
 Add to MetaCart
Automatic tool support for scheduling applications on multiprocessor platforms is of paramount importance both to guarantee critical application demands and to keep development costs down. In this paper, we present GAST, an objectoriented evaluation environment for multiprocessor assignment and scheduling techniques. GAST is based on a decomposition approach where existing assignment and scheduling techniques have been broken down into a set of common operations. By combining these operations into a complete scheduling process, GAST offers a powerful toolbox of existing assignment and scheduling techniques. GAST has been implemented on several popular operating systems and is accompanied by a graphic visualization tool that allows for flexible interaction with the application scheduling process. 1 Introduction For economical reasons, singleprocessor computers have traditionally been the only viable option for many computer system designers. This has, in turn, limited the sphere of f...
Preemptive Scheduling with Variable Profile, Precedence Constraints and Due Dates
 Discrete Applied Mathematics
, 1993
"... This paper is concerned with the problem of scheduling preemptive tasks subject to precedence constraints in order to minimize the maximum lateness and the makespan. The number of available parallel processors is allowed to vary in time. It is shown that when an Earliest Due Date first algorithm pro ..."
Abstract

Cited by 9 (2 self)
 Add to MetaCart
This paper is concerned with the problem of scheduling preemptive tasks subject to precedence constraints in order to minimize the maximum lateness and the makespan. The number of available parallel processors is allowed to vary in time. It is shown that when an Earliest Due Date first algorithm provides an optimal nonpreemptive schedule for unitexecution time (UET) tasks, then the preemptive priority scheduling algorithm, referred to as Smallest Laxity First, provides an optimal preemptive schedule for realexecutiontime (RET) tasks. When the objective is to minimize the makespan, we get the same kind of result between Highest Level First schedules solving nonpreemptive tasks with UET and the Longest Remaining Path first schedule for the corresponding preemptive scheduling problem with RET tasks. These results are applied to four specific profile scheduling problems and new optimality results are obtained. Keywords: Preemptive Scheduling, List Schedule, Priority Schedule, Variable P...
Effective Complexity Reduction for Optimal Scheduling of Distributed RealTime Applications
 Proc. of the IEEE Int'l Conf. on Distributed Computing Systems
, 1999
"... The application of optimal search strategies to scheduling for distributed realtime systems is, in general, plagued by an inherent computational complexity. This has effectively prevented the integration of strategies such as branchandbound (B&B) in scheduling frameworks and tools used in practice ..."
Abstract

Cited by 8 (6 self)
 Add to MetaCart
The application of optimal search strategies to scheduling for distributed realtime systems is, in general, plagued by an inherent computational complexity. This has effectively prevented the integration of strategies such as branchandbound (B&B) in scheduling frameworks and tools used in practice today. To show that optimal scheduling is, in fact, a viable alternative for many realtime scheduling scenarios, we propose an approach that can reduce the average search complexity to levels comparable with that of a polynomialtime heuristic. Our approach is based on making intelligent choices in the selection of strategies for search tree vertex traversal and task deadline assignment. More specifically, we conjecture that effective complexity reduction is achieved by (i) traversing vertices in the search tree in a depthfirst fashion and (ii) assigning local task deadlines that are nonoverlapping fractions of the application endtoend deadline. Through an extensive experimental study, w...
Scheduling UET, UCT dags with release dates and deadlines
, 1995
"... The problem of scheduling precedence graphs for which every task has to be executed in a nonuniform interval is considered, with interprocessor communication delays. For the following classes of graphs we will present a polynomial time algorithm that finds minimumlateness schedules. 1. Outforests o ..."
Abstract

Cited by 5 (2 self)
 Add to MetaCart
The problem of scheduling precedence graphs for which every task has to be executed in a nonuniform interval is considered, with interprocessor communication delays. For the following classes of graphs we will present a polynomial time algorithm that finds minimumlateness schedules. 1. Outforests on two processors. 2. Seriesparallel graphs and opposing forests with the least urgent parent property (to be defined) on two processors. 3. Inforests with the least urgent parent property on m processors.
Scheduling Superblocks with BoundBased Branch Tradeoffs
 n. 8
, 2001
"... AbstractÐSince instruction level parallelism in basic blocks is often limited, compilers increase performance by creating superblocks that allow operations to be issued speculatively. This is difficult in general because each branch competes for the processor's limited resources. Previous work manag ..."
Abstract

Cited by 4 (0 self)
 Add to MetaCart
AbstractÐSince instruction level parallelism in basic blocks is often limited, compilers increase performance by creating superblocks that allow operations to be issued speculatively. This is difficult in general because each branch competes for the processor's limited resources. Previous work manages the performance tradeoffs that exist between branches only indirectly. We show here that dependence and resource constraints can be used to gather explicit knowledge about scheduling tradeoffs between branches. This paper's first contribution is a set of new, tighter lower bounds on the execution times of superblocks that specifically account for the dependence and resource conflicts between pairs of branches. This paper's second contribution is a novel superblock scheduling heuristic that finds high performance schedules by determining the operations that each branch needs to be scheduled early and selecting branches with compatible needs that favor beneficial branch tradeoffs. Performance evaluations for superblocks from SPECint95 indicate that our bounds are very tight and that our scheduling heuristic outperforms wellknown superblock scheduling algorithms. Index TermsÐSuperblock, scheduling heuristic, lower bound, ILP compiler technique. 1
On Scheduling Cycle Shops: Classification, Complexity And Approximation
"... . This paper considers problems of finding nonperiodic and periodic schedules in a cycle shop which is a special case of a job shop but an extension of a flow shop. The cycle shop means the machine environment where all jobs have to pass the machines over the same route like in a flow shop but so ..."
Abstract

Cited by 4 (0 self)
 Add to MetaCart
. This paper considers problems of finding nonperiodic and periodic schedules in a cycle shop which is a special case of a job shop but an extension of a flow shop. The cycle shop means the machine environment where all jobs have to pass the machines over the same route like in a flow shop but some of the machines in the route can be met more than once. We propose a classification of cycle shops and show that recently studied reentrant flow shops, robotic flow shops, loop reentrant flowshops and V shops are special cases of cycle shops. Problems solvable in polynomial time, pseudopolynomial time, NPhard problems and performance guarantee approximations are presented. Related earlier results are surveyed. 1.
Lower Bounds on PrecedenceConstrained Scheduling for Parallel Processors
 Proc. the 29th Int’l Conf. Parallel Processing
, 2000
"... We consider two general precedenceconstrained scheduling problems that have wide applicability in the areas of parallel processing, high performance compiling, and digital system synthesis. These problems are intractable so it is important to be able to compute tight bounds on their solutions. A ti ..."
Abstract

Cited by 2 (0 self)
 Add to MetaCart
We consider two general precedenceconstrained scheduling problems that have wide applicability in the areas of parallel processing, high performance compiling, and digital system synthesis. These problems are intractable so it is important to be able to compute tight bounds on their solutions. A tight lower bound on makespan scheduling can be obtained by replacing precedence constraints with release and due dates, giving a problem that can be efficiently solved. We demonstrate that recursively applying this approach yields a bound that is provably tighter than other known bounds, and experimentally shown to achieve the optimal value at least 86.5% of the time over a synthetic benchmark. We compute the best known lower bound on weighted completion time scheduling by applying the recent discovery of a new algorithm for solving a related scheduling problem. Experiments show that this bound significantly outperforms the linear programmingbased bound. We have therefore demonstrated that combinatorial algorithms can be a valuable alternative to linear programming for computing tight bounds on large scheduling problems.