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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
Abstract
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
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