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Desynchronized Pfair Scheduling on Multiprocessors UmaMaheswari C. Devi and James H. Anderson

Summary: Desynchronized Pfair Scheduling on Multiprocessors
UmaMaheswari C. Devi and James H. Anderson
Department of Computer Science, The University of North Carolina, Chapel Hill, NC
Pfair scheduling, currently the only known way of optimally scheduling recurrent real-time tasks
on multiprocessors, imposes certain requirements that may limit its practical implementation. In this
paper, we address one such limitation -- which requires processor time to always be allocated in units
of fixed-sized quanta that are synchronized across processors -- and determine the impact of relaxing
it. We show that if this requirement is relaxed, then under an otherwise-optimal Pfair scheduling algo-
rithm, deadlines are missed by at most one quantum only, which is sufficient to provide soft real-time
guarantees. This result can be shown to extend to most prior work on Pfair scheduling: In general,
tardiness bounds guaranteed by previously-proposed suboptimal Pfair algorithms are worsened by at
most one quantum only.

Work supported by NSF grants CCR 0204312, CCR 0309825, and CCR 0408996.
1 Introduction
A real-time system, unlike a non-real-time sys-
tem, has to meet certain timing constraints to
be correct. Such timing constraints are typically
specified as deadline requirements. Tasks in a


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


Collections: Computer Technologies and Information Sciences