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,firstname.lastname@example.org
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