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Summary: Pfair Scheduling: Beyond Periodic Task Systems
James H. Anderson and Anand Srinivasan
Department of Computer Science
University of North Carolina
Chapel Hill, NC 27599-3175
Phone: (919) 962-1757
Fax: (919) 962-1799
E-mail: fanderson,anandsg@cs.unc.edu
July 2000
Abstract
Prior work on multiprocessor Pfair scheduling algorithms has almost exclusively focused on synchronous,
periodic task systems. Under Pfair scheduling, each task is broken into quantum-length subtasks, each of
which must execute within a \window" of time slots. These windows divide each period of a task into
subintervals of approximately equal length. \Early-release" fair (ERfair) scheduling was recently proposed
as a work-conserving variant of Pfair scheduling in which subtasks within the same job are allowed to execute
before their Pfair windows.
In this paper, we consider variants of Pfair and ERfair scheduling in which subtasks may be released late,
i.e., there may be separation between consecutive windows of the same task. We call such tasks intra-sporadic
tasks. The notion of an intra-sporadic task generalizes that of a sporadic task (which in turn generalizes the
notion of an asynchronous task). If early releases are allowed, then the intra-sporadic task model provides
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