Totally Clairvoyant Scheduling with Relative Timing Constraints

Abstract

Public reporting burden for tbis collection of informetion is estimated to overage 1 hour per response, including tlie time for reviewing instructions, si the collection of information. Send comments regerding this burden estimate or any other aspect of this collection of information, including su Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, PB|. AFRL-SR-AR-TR-03-reviewing iformalian MmVl\mmV1 (Leave blank) REPORT DATE REPORT TYPE AND DATES COVERED01 JAN 02-31 DEC 02 TITLE AND SUBTITLE TOALY CLAIRVOYANT SCHEDULING WITH RELATIVE TIMING CONSTRAINTS AUTHOR(S)K. SUBRAMANI PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)WEST VIRGINIA UNIVERSITY MORGANTOWN, WV SPONSORINGIMONITORING AGENCY NAMEIS) AND ADDRESS(ES)AFOSR ABSTRACT IMaximum 200 words)Traditional scheduling models assume that the execution time of a job in a periodic job-set is constant in every instance of its execution. This assumption does not hold m real-time systems wherein job execution time is known to vary. A second feature of traditional models is their lack of expressiveness, in that constraints more complex than precedence constraints (for instance, relative timing constraints) cannot be modeled. Thirdly, the schedulability of a real-time system depends upon the degree of clairvoyance afforded to the dispatcher. In this paper, we shall discuss Totally Clairvoyant Scheduling, as modeled within the E-T-C scheduling framework. We show that instantiation of the scheduling framework capmres the central issues in a real-time flow-shop scheduling problem and design a polynomial time sequential algorithm for the same. We also introduce an error-minimizing performance metric called Violation Degree and establish that optimizing this metric in a Totally Clairvoyant Scheduling System in NP-Hard. . We provide polynomial time algorithms for the case in which the constraints between jobs are strict diff'erence constraints, also called "standard constraints". We also show that a Performance Metric Optimization problem is NP-Hard.[Suba] represents an off'shoot of the main thrust of our work. While working on short refutations for Totally Clairvoyant Scheduling systems, it occurred to us that tree-like resolution refutations of 2SAT formulas could be determined in polynomial time.We have recently proposed the addition of optimization functions to Clairvoyant Scheduling, as well as parallel strategies for large scale problems. This proposal is currently under consideration for funding by AFOSR. AcknowledgementsWe thank Major Juan Vasquez for his encouragement and willingness to explore new ideas in basic research. We hope that the attached papers will vindicate his faith in us. Traditional scheduling models assume that the execution time of a job in a periodic job-set is constant in every instance of its execution. This assumption does not hold in real-time systems wherein job execution time is known to vary. A second feature of traditional models is their lack of expressiven...

On-Line Algorithms, Real Time, the Virtue of Laziness, and the Power of Clairvoyance

“…The latter situation typically arises in interactive systems, while clairvoyance can be used to model batched systems. See, for example, [10,11,37,42], and [38] for a survey on scheduling.…”