Workstation support for time-critical applications [chapter]

James G. Hanko, Eugene M. Kuerner, J. Duane Northcutt, Gerard A. Wall
1992 Lecture Notes in Computer Science  
The first workshop session was dedicated to the issue of real-time support for multimedia applications. Audio and video are commonly referred to as time-dependent continuous media. Their timing dependencies need proper support by the computer system. This calls for the use of classical techniques from real-time computing. Yet, audio and video have slightly different requirements than traditional real-time applications. During the first talk, Jim Hanko from SUN Microsystems presented a paper co:
more » ... authored with Eugene Kuerner, Duane Northcutt, and Gerald Wall on "Workstation Support for Time-Critical Applications," introducing the topic. The initial thesis of the talk was that while today's workstations have a great deal of computational power, this power cannot be effectively delivered to support multimedia applications because system resources are not organized and managed in the necessary manner. Existing workstations provide abundant CPU capacity, but poor I/O support. While in traditional computing the lack of I/O power can be masked by caching, continuous-media applications that do not reuse data cannot benefit from it. Workstations do not dedicate resources to I/O processing as mainframes do. The single CPU has to help out to perform I/O, constituting a performance bottleneck. That the CPU is scheduled based on "fairness" rather than urgency worsens the problem. The authors point out that existing real-time systems cannot be used to overcome this problem because they rely on deterministic behavior and known load, assumptions not well suited for a workstation environment. Their statement that existing real-time scheduling techniques such as rate-monotonic scheduling are not appropriate for multimedia has, however, generated opposition from the audience. A new resource management technique, Time-Driven Resource Management (TDRM), is proposed. The technique bases its decisions on the requester's deadline, importance, and expected resource requirements. The technique does not provide sharp guarantees for a certain quality of service, it rather encourages "graceful degradation." The matter of how a resource management technique should affect system behavior was subject to major discussion. Many reservation schemes proposed (e.g., those from Anderson or Ferrari of the University of California at Berkeley) provide a fixed quality of service and reject new service requests when the provision of the service would endanger previously given guarantees. To a user, this may mean that his request for retrieving a video is turned down. Such a system can be compared to the telephone system: If a busy signal is received, the user will have to wait and dial again. Adaptive policies provide more flexibility, but cannot guarantee f'bxed quality levels. It was mainly agreed that an ideal resource management technique should be a combination of both cases. Some fictitious "costs" can be chosen to decide which ap-Current workstations have a great deal of computational power. However, this power cannot be effectively delivered to support time-critical applications because the system resources are not organized nor managed in the necessary manner. What is needed is hardware and software platform technology that manages (i.e., acquires, processes, transfers, coordinates, and delivers) these time-critical data streams. This research into properly constructing, organizing, and managing system resourcea (according to principles of time-driven resource management) will enable workstations to solve many problems currently handled by dedicated-function embedded systems or point-solution add-on devices, while retaining the essential characteristics of the distributed workstation system environment.
doi:10.1007/3-540-55639-7_1 fatcat:guq3tfp4gveajlkq34gh2p7wr4