Summary: E#cient Scheduling of Soft Realtime Applications on
Anand Srinivasan and James H. Anderson
Department of Computer Science
University of North Carolina at Chapel Hill
In soft realtime applications, tasks are allowed to miss their deadlines. Thus, lesscostly scheduling
algorithms can be used at the price of occasional violations of timing constraints. This may be acceptable if
reasonable tardiness bounds (i.e., bounds on the extent to which deadlines may be missed) can be guaranteed.
In this paper, we consider soft realtime applications implemented on multiprocessors. Pfair scheduling
algorithms are the only known means of optimally scheduling hard realtime applications on multiprocessors.
For this reason, we consider the use of such algorithms here. In the design of Pfair scheduling algorithms,
devising schemes to correctly break ties when several tasks have the same deadline is a critical issue. Such
tiebreaking schemes entail overhead that may be unacceptable or unnecessary in soft realtime applications.
In this paper, we consider the earliest pseudodeadline first (EPDF) Pfair algorithm, which avoids this
overhead by using no tiebreaking information. Our main contributions are twofold. First, we establish a
condition for ensuring a tardiness of at most one quantum under EPDF. This condition is very liberal and
should often hold in practice. Second, we present simulation results involving randomlygenerated task sets,