A. Kassler, B. Reiterer, and J. Kaiser (Germany)
CPU Scheduling, Quality of Service, Multimedia
Distributed multimedia applications have scheduling require ments which substantially differ from those in hard real-time sys tems. The system load in a multimedia system is widely varying and scheduling schemes based on the worst-case execution time assumption are infeasible from the costs point of view. Although QoS requirements strongly demand that deadlines are not missed, this point can be treated in a probabilistic way in contrast to the hard real-time safety critical field. As a consequence, problems of transient overload occur and have to be an intrinsic element of a scheduling scheme. Flexible mechanisms to monitor the system and to adapt to changing load requirements have to be incorpo rated. This paper presents a general architectural framework to schedule soft real-time multimedia tasks and guarantee a negoti ated amount of processor share in the presence of competing ap plications. It comprises the necessary components for admittance test, resource controlling and on-line system monitoring which form the basis for an adaptive scheduling approach. We provide preliminary results and analyze different adaptation policies for multiple adaptive threads in our Windows NT implementation.
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