Next generation real-time systems will require greater flexibility and predictability than is commonly found in today's systems. These future systems include the space sta-tion, integrated vision/robotics/AI systems, collections of humans/robots coordinating to achieve common objectives (usually in hazardous environments such as undersea explo-ration or chemical plants), and various command and control applications. The Spring kernel is a research oriented kernel designed to form the basis of a flexible, hard real-time operating system for such applications. Our approach challenges several basic assump-tions upon which most current real-time operating systems are built and subsequently advocates a new paradigm based on the notion of predictability and a method for on-line dynamic guarantees of deadlines. The Spring kernel is being implemented on a network of (68020 based) multiprocessors called SpringNet. 1

Quality of service (QoS) has been receiving wide attention in recent years in many research communities including networking, multimedia systems, real-time systems and distributed systems. In large distributed systems such as those used in defense systems, on-demand service and inter-networked systems, applications contending for system resources must satisfy timing, reliability and security constraints as well as application-specific quality requirements. Allocating sufficient resources to different applications in order to satisfy various requirements is a fundamental problem in these situations. A basic yet flexible model for performance-driven resourceallocations can thereforebe useful in making appropriate tradeoffs. In this paper, we present an analytical model for QoS management in systems which must satisfy application needs along multiple dimensions such as timeliness, reliable delivery schemes, cryptographic security and data quality. We refer to this model as Q-RAM (QoS-based Res...

Design-to-time is an approach to problem-solving in resource-constrained domains where: multiple solution methods are available for tasks, those solution methods make tradeoffs in solution quality versus time, and satisficing solutions are acceptable. Design-to-time involves designing a solution to a problem that uses all available resources to maximize the solution quality within the available time. This paper defines the design-to-time approach in detail, contrasting it to the anytime algorithm approach, and presents a heuristic algorithm for designto -time real-time scheduling. Our blackboard architecture that implements the design-to-time approach is discussed and an example problem and solution from the Distributed Vehicle Monitoring Testbed (DVMT) is described in detail. Experimental results, generated using a simulation, show the effects of various parameters on scheduler performance. Finally we discuss future research goals and plans. 1 This work was partly supported by the Of...

RAM) proposed in [20] presented an analytical approach for satisfying multiple quality-of-service dimensions in a resource-constrained environment. Using this model, available system resources can be apportioned across multiple applications such that the net utility that accrues to the end-users of those applications is maximized. In this paper, we present several practical solutions to allocation problems that were beyond the limited scope of [20]. First, we show that the Q-RAM problem of finding the optimal resource allocation to satisfy multiple QoS dimensions (at least one of which is dependent on another) is NP-hard. We then present a polynomial solution for this resource allocation problem which yields a solution within a provably fixed and short distance from the optimal allocation. Secondly, [20] dealt mainly with the problem of apportioning a single resource to satisfy multiple QoS dimensions. In this paper, we study the converse problem of apportioning multiple resources to satisfy a single QoS dimension. In practice, this problem becomes complicated, since a single QoS dimension perceived by the user can be satisfied using different combinations of available resources. We show that this problem can be formulated as a mixed integer programming problem that can be solved efficiently to yield an optimal resource allocation. Finally, we also present the run-times of these optimizations to illustrate how these solutions can be applied in practice. We expect that a good understanding of these solutions will yield insights into the general problem of apportioning multiple resources to satisfy simultaneously multiple QoS dimensions of multiple concurrent applications. 1.

Coordination, as the act of managing interdependencies between activities, is one of the central research issues in Distributed Artificial Intelligence. Many researchers have shown that there is no single best organization or coordination mechanism for all environments. Problems in coordinating the activities of distributed intelligent agents appear in many domains: the control of distributed sensor networks; multi-agent scheduling of people and/or machines; distributed diagnosis of errors in local-area or telephone networks; concurrent engineering; `software agents' for information gathering. The design of coordination mechanisms for group...

Abstract: This paper describes the Chimera II Real-time Operating System, which has been developed for advanced sensor-based control applications. It has been designed as a local operating system, to be used in conjunction with a global operating system. It executes on one or more single board computers in a VMEbus-based system. Advanced sensor-based control systems are both statically and dynamically reconfigurable. As a result, they require many special features, which are currently not found in commercial real-time operating systems. In this paper, we present several design issues for such systems, and we also present the features we have developed and implemented as part of Chimera II. These features include a real-time kernel with dynamic scheduling, global error handling, user signals, and two levels of device drivers; an enhanced collection of interprocessor communication mechanisms, including global shared memory, spin-locks, remote semaphores, priority message passing, global state variable tables, multiprocessor servo task control, and host workstation integration; and several support utilities, including a UNIX C and math libraries, a matrix library, a command interpreter library, and a configuration file library. Chimera II is currently being used with a variety of systems, including the CMU Direct Drive Arm II, the CMU Reconfigurable Modular Manipulator System, the Troikabot System for Rapid Assembly, and the Self-Mobile Space Manipulator. I.

Recent results in the application of... this paper. The review takes the form of an analysis of the problems presented by different application requirements and characteristics. Issues covered include uniprocessor and multiprocessor systems, periodic and aperiodic processes, static and dynamic algorithms, transient overloads and resource usage. Protocols that limit and reduce blocking are discussed. Considerations are also given to scheduling Ada tasks.

The advent of QoS-sensitive Internet applications such as multimedia, the inception of priced online services, and the proliferation of performance-critical applications such as online trading raise a need for building server systems with guaranteed performance. Unlike embedded software systems designed for a particular special-purpose platform, the new applications should be designed to run on different heterogeneous platforms, provide soft performance guarantees commensurate with platform capacity, and adapt efficiently to upgrades in platform resources over the system's lifetime. The problem of profiling the application for the purposes of providing QoS guarantees on each new platform becomes a significant undertaking. Automated profiling mechanisms must be built to enable efficient computing of QoS guarantees tailored to platform capacity and facilitate wide deployment of soft performance-guaranteed systems on heterogeneous platforms.

The proliferation of high-volume time-critical web services such as online trading calls for a scalable server design that allows meeting individual response-time guarantees of real-time transactions. A main challenge is to honor these guarantees despite unpredictability in incoming server load. The extremely high volume of real-time service requests mandates constant-time scheduling and schedulability analysis algorithms (as opposed to polynomial or logarithmic ones in the number of current requests).

The Kernel Tool Kit (KTK) is an object-based operating system kernel and parallel programming library that offers explicit support for on- and off-line program configuration. Specifically, KTK allows the specification of attributes for object classes, object instances, state variables, operations and object invocations. Attributes are interpreted by policy classes that may be varied separately from the abstractions with which they are associated. They can be used to vary object internal implementation and semantics without affecting the methods being invoked. In this paper, the runtime configuration of KTK attributes is shown to improve the runtime performance of multiprocessor applications. KTK is layered on a portable and configurable parallel programming substrate, a Mach Cthreads compatible runtime library. College of Computing Georgia Institute of Technology Atlanta, Georgia 30332--0280 1 Configuring parallel systems for performance It is well-known that the performance of a p...