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Using Supertasks to Improve Processor Utilization in Multiprocessor Real-time Systems

Summary: Using Supertasks to Improve Processor Utilization in
Multiprocessor Real-time Systems
Philip Holman and James H. Anderson
Department of Computer Science
University of North Carolina
Chapel Hill, NC 27599-3175
E-mail: {holman,anderson}@cs.unc.edu
December 2002
We revisit the problem of supertasking in Pfair-scheduled multiprocessor systems. In this approach, a set
of tasks, called component tasks, is assigned to a server task, called a supertask, which is then scheduled as an
ordinary Pfair task. Whenever a supertask is scheduled, its processor time is allocated to its component tasks
according to an internal scheduling algorithm. Hence, supertasking is an example of hierarchal scheduling.
In this paper, we present a generalized "reweighting" algorithm. The goal of reweighting is to assign
a fraction of a processor to a given supertask so that all timing requirements of its component tasks are
met. The generalized reweighting algorithm we present breaks new ground in three important ways. First,
component tasks are permitted to have non-integer execution costs. Consequently, supertasking can now be
used to ameliorate schedulability loss due to the integer-cost assumption of Pfair scheduling. To the best of
our knowledge, no other techniques have been proposed to address this problem. Second, blocking terms are
included in the analysis. Since blocking terms are used to account for a wide range of behaviors commonly


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


Collections: Computer Technologies and Information Sciences