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Guaranteeing Pfair Supertasks by Reweighting Philip Holman and James H. Anderson

Summary: Guaranteeing Pfair Supertasks by Reweighting 
Philip Holman and James H. Anderson
Department of Computer Science
University of North Carolina
Chapel Hill, NC 27599-3175
Phone: (919) 962-1757
Fax: (919) 962-1799
E-mail: fholman,andersong@cs.unc.edu
May 2001
We consider the \supertask" approach, proposed by Moir and Ramamurthy at RTSS '99 as means for
supporting non-migratory tasks in Pfair-scheduled systems. In this approach, tasks bound to the same pro-
cessor are combined into a single supertask, which is scheduled as an ordinary Pfair task; when a supertask
is scheduled, one of its component tasks is selected for execution. Unfortunately, while Moir and Rama-
murthy's paper suggests that supertasking is a promising approach, counterexamples presented by them
show that non-migratory tasks can actually miss their deadlines when supertasking is used in conjunction
with all known Pfair scheduling algorithms.
In this paper, we show that such deadline misses can be prevented by in ating each supertask's utilization.
We present experimental evidence that shows that the required in ation factors should be small in practice.
We also show that these in ation factors usually can be reduced if, instead of being scheduled in a Pfair


Source: Anderson, James - Department of Computer Science, University of North Carolina at Chapel Hill


Collections: Computer Technologies and Information Sciences