Summary: Efficient Scheduling of Soft Real-time Applications on
Anand Srinivasan and James H. Anderson
Department of Computer Science
University of North Carolina at Chapel Hill
In soft real-time applications, tasks are allowed to miss their deadlines. Thus, less-costly 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 real-time applications implemented on multiprocessors. Pfair scheduling
algorithms are the only known means of optimally scheduling hard real-time 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
tie-breaking schemes entail overhead that may be unacceptable or unnecessary in soft real-time applications.
In this paper, we consider the earliest pseudo-deadline first (EPDF) Pfair algorithm, which avoids this
overhead by using no tie-breaking 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 randomly-generated task sets,