Existing real-time research focuses on how to formulate. model and enforce timeliness guarantees for task sets whose correctness has a temporal aspect. However; the resulting systems often exhibit poor resource utilization due to the resource scheduler reserving more resources than required in order to ensure that admitted schedules can be satisfied under worst case conditions. Weakening the guarantees leads to the known concepts of firm and soft real-time tasks, butt we think the paradigm needs to be shifted further,: reifying efficient utilization. With Quality-Assuring Scheduling (QAS) we presented such an algorithm. However: its practical applicability is restricted to uniform and harmonic periods, due to its complexity for arbitrary periods. To overcome this limitation, we introduce Quality-Rate-Monotonic Scheduling (QRMS), which, although slightly more pessimistic, is less complex compared to QAS. Thee admission control is again based on a probabilistic model to ensure that a requested fraction of jobs is successfully executed. Thus the amount of missed deadlines can be externally controlled, even in sustained overload situations.

Scheduling disk requests with service guarantees has to bring the demand to meet guarantees in line with the need to optimize disk utilization. This paper presents the design, implementation, and experimental evaluation of a disk-scheduling framework which optimizes the disk utilization under the constraints of both hard and statistical service guarantees. The framework is based on two principles: 1) upon each scheduling decision, the calculation of a subset of the outstanding disk requests such that all service guarantees can be enforced under worst-case assumptions; and 2) the scheduling of this subset based on the rotational position of requests in order to improve the disk utilization. Results are presented through an implementation of the scheduling framework in DROPS, the Dresden real-time operating system.

Timely transfer of long, continuous data streams and handling data omission are stringent requirements of multimedia applications. To cope with these requirements, we extend well known mechanisms for inter-address-space data transmission, such as zero-copy and fast IPC, by the notion of time. Therefore, we add a time track to data streams and add mechanisms to limit the validity of data. For cases of overload we add notification and revocation techniques.

We present a unified model for admission and scheduling, applicable for various active resources such as CPU or disk to assure a requested quality in situations of temporary overload. The model allows us to predict and control the behavior of applications based on given quality requirements. It uses the variations in the execution time, i.e., the time any active resource is needed We split resource requirements into a mandatory part which must be available and an optional part which should be available as often as possible but at least with a certain percentage. In combination with a given distribution for the execution time we can move away from worst-case reservations and drastically reduce the amount of reserved resources for applications which can tolerate occasional deadline misses. This increases the number of admittable applications. For example, with negligible loss of quality our system can admit more than two times the disk bandwidth than a system based on the worst-case. Finally, we validated the predictions of our model by measurements using a prototype real-time system and observed a high accuracy between predicted and measured values.

This paper describes a technique to effectively isolate mobile objects or processes that execute downloaded, potentially suspicious programs. It relies on wish lists, trust lists and capability lists. Wish lists are carried along with programs or mobile objects and denote the resources requested by the program to do what it claims to do. Wish lists are transformed into capability lists when downloaded programs are started. Trust lists reside on stations and are used to determine which members of wish lists are taken over into capability lists. The capability lists are enforced during the execution of programs. All lists are symbolic to enable their interpretation in heterogeneous environments. The paper describes the technique, its integration in a Linux environment and first experiences.