Schwiegelshohn - University Dortmund Robotics Research...

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University Dortmund Robotics Research Institute Information Technology Job Scheduling Uwe Schwiegelshohn EPIT 2007, June 5 Ordonnancement
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2 Content of the Lecture Q What is job scheduling? Q Single machine problems and results Q Makespan problems on parallel machines Q Utilization problems on parallel machines Q Completion time problems on parallel machines Q Exemplary workload problem
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3 Examples of Job Scheduling Q Processor scheduling · Jobs are executed on a CPU in a multitasking operating system. · Users submit jobs to web servers and receive results after some time. · Users submit batch computing jobs to a parallel processor. Q Bandwidth scheduling · Users call other persons and need bandwidth for some period of time. Q Airport gate scheduling · Airlines require gates for their flights at an airport. Q Repair crew scheduling · Customer request the repair of their devices.
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4 Job Properties Q Independent jobs · No known precedence constraints O Difference to task scheduling Q Atomic jobs · No job stages O Difference to job shop scheduling Q Batch jobs · No deadlines or due dates O Difference to deadline scheduling p j processing time of job j r j release date of job j earliest starting time importance of the job parallelism of the job w j weight of job j m j size of job j
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5 Machine Environments Q 1: single machine · Many job scheduling problems are easy. Q P m : m parallel identical machines · Every job requires the same processing time on each machine. · Use of machine eligibility constraints M j if job j can only be executed on a subset of machines O Airport gate scheduling: wide and narrow body airplanes Q Q m : m uniformly related machines · The machines have different speeds v i that are valid for all jobs. · In deterministic scheduling, results for P m and Q m are related. · In online scheduling, there are significant differences between P m and Q m . Q R m : m unrelated machines · Each job has a different processing time on each machine.
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6 Restrictions and Constraints Q Release dates r j Q Parallelism m j · Fixed parallelism: m j machines must be available during the whole processing of the job. · Malleable jobs: The number of allocated machines can change before or during the processing of the job. Q Preemption · The processing of a job can be interrupted and continued on another machine. · Gang scheduling: The processing of a job must be continued on the same machines. Q Machine eligibility constraints M j Q Breakdown of machines · m(t): time dependent availability rarely discussed in the literature
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7 Objective Functions Q Completion time of job j: C j Q Owner oriented: · Makespan: C max =max (C 1 ,...,C n ) O completion time of the last job in the system · Utilization U t : Average ratio of busy machines to all machines in the interval (0,t] for some time t.
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Schwiegelshohn - University Dortmund Robotics Research...

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