Summary: Early­Release Fair Scheduling \Lambda
James H. Anderson and Anand Srinivasan
Department of Computer Science, University of North Carolina, Chapel Hill, NC 27599­3175
Phone: (919) 962­1757 Fax: (919) 962­1799 E­mail: fanderson,anandsg@cs.unc.edu
December 1999
Abstract
We present a variant of Pfair scheduling, which we call early­release fair (ERfair) scheduling. Like con­
ventional Pfair scheduling, ERfair scheduling algorithms can be applied to optimally schedule periodic tasks
on a multiprocessor system in polynomial time. However, ERfair scheduling differs from Pfair scheduling in
that it is work conserving. As a result, average job response times may be much lower under ERfair schedul­
ing than under Pfair scheduling, particularly in lightly­loaded systems. In addition, runtime costs are lower
under ERfair scheduling. This is because, in Pfair­scheduled systems, significant bookkeeping information
is required to determine when a job of a task is and is not eligible for execution. In an ERfair system,
this bookkeeping information is not required because, once released, a job continues to be eligible until it
completes. To the best of our knowledge, ERfair scheduling is the first truly work­conserving scheduling
discipline for periodic task systems that is optimal for multiprocessors.
Keyword: fairness, multiprocessors, optimality, Pfair, real­time scheduling, work­conserving schedulers.
\Lambda Work supported by NSF grants CCR 9732916 and CCR 9972211. The first author was also supported by an Alfred P. Sloan
Research Fellowship.


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

Collections: Computer Technologies and Information Sciences