The Challenges of Real-Time AI

The research agendas of two major areas of computer science are converging: Artificial Intelligence (AI) methods are moving towards more realistic domains requiring real-time responses, and real-time systems are moving towards more complex applications requiring intelligent behavior. Together, they meet at the crossroads of interest in "real-time intelligent control," or "real-time AI." This subfield is still being defined by the common interests of researchers from both real-time and AI systems. As a result, the precise goals for various real-time AI systems are still in flux. This paper describes an organizing conceptual structure for current real-time AI research, clarifying the different meanings this term has acquired for various researchers. Having identified the various goals of real-time AI research, we then specify some of the necessary steps towards reaching those goals. This in turn enables us to identify promising areas for future research in both AI and real-time systems techniques. (Also cross-referenced as UMIACS-TR-94-69

A Dynamic Programming Algorithm for Cache/Memory . . .

This correspondence presents an algorithm for optimally partitioning two-level memory systems for deterministic, real-time performance. Further, the algorithm finds the optimal solution in polynomial time, which supports on-line reconfiguration of memory resources in response to changing requirements. Index Terms - Real-Time, Multi-Level Memories, Schedulability, Utilization, Dynamic programming. I INTRODUCTION Many computing systems have multi-level memory hierarchies with small, fast memory close to the processing engine backed by a larger, slower memory. The purpose for such hierarchies is to balance the trade-offs between the cost of faster memories and the performance gains which they provide. The faster memories usually take the form of caches or local RAM, while the slower memories are typically system memory, ROM, or disk. For example, systems such as the Intel i960CA or digital signal processors like the AT&T DSP3210 or the Texas Instruments TMS320XX use high speed on-chip R..

ARTIFACT: An Experimental Real-Time Window System

: Multimedia and advanced real-time systems integrate a variety of applications and media types in one environment, many of which have timing properties which are not supported by current window systems running in multitasking environments. This paper discusses several key aspects to designing window systems which support continuous media and other real-time applications. These design considerations were used to construct ARTIFACT, a window system designed to investigate issues in building real-time window systems. Several of the behaviors of a prototype implementation of ARTIFACT are described, along with preliminary scheduling models and avenues for further research. Keywords: real-time systems, operating system support, window systems, multimedia support, scheduling theory 1. Introduction Multimedia systems integrate a variety of media types into a unified display environment. Some media types, such as text and static graphics, have been in use for quite some time. Other types, su..

An Evaluation of the Graceful Degradation Properties of Real-Time Schedulers

Real-time, fault-tolerant systems require schedulers that provide graceful degradation during transient overloads resulting from fault recovery workloads or other system uncertainties. We initially hypothesize that a scheduler ideally suited to this environment should dispatch tasks using only response time criterion as long as all deadlines can be met, and that in the presence of overload the best a scheduler can do is semantic-driven load shedding. By temporarily eliminating less important tasks, the more intelligent scheduling algorithms were expected to service the more important tasks well without harming the non-critical tasks unnecessarily. Experimentally we then show this hypothesis to be false. On-line tracking of system load does not provide enough information about future load to effectively trigger semantic-driven load shedding. Simpler algorithms can insure predictable behavior, but sacrifice fault-free schedulability to do so. We show that a compromise can be reached by d..

Supporting Embedded System Design Capture, Analysis and Navigation

This paper presents a COTS- (Commercial-Off-TheShelf) oriented view of the embedded systems design space. It summarizes a set of frameworks capturing a significant portion of this design space along with a selected set of methods. These methods enable engineers to easily generate and quantitatively evaluate points within the design space. This paper also briefly discusses the design space navigation problem. The frameworks and methods are restricted to address performance/resource management issues. This paper shows how the design capture frameworks can establish and maintain performance baselines for large-scale, longlife, embedded systems. 1 Introduction Large-scale, complex, embedded systems were traditionally in the domain of defense systems, transportation systems and industrial systems. These systems were generally constructed using application software hosted upon custom operating systems, and custom hardware. The time lag and costs associated with custom design solutions are n..

Conventional Early Token Release Scheduling Models for the IEEE 802.5 Token Ring

We develop analytical scheduling models for both the original IEEE 802.5 token ring protocol and a recent extension to the original protocol that allows early token release (ETR). A scheduling model is an abstraction that supports reasoning about the timing correctness of a given set of real-time messages scheduled on the network. Scheduling analysis of the original IEEE 802.5 token ring protocol has previously been discussed in [SM89] and [Ple92] in the context of improving responsiveness of soft deadline aperiodic messages. In contrast, this paper develops schedulability conditions for arbitrary periodic message sets. The main contributions of this work are: Scheduling models for both the original protocol and ETR protocol; comparison for maximum achievable utilizations for the two protocols; comparison between the original protocol and ETR from a schedulability viewpoint. We also demonstrate the utility of our scheduling models to select network operating parameters such as of maxim..

Disk Scheduling for Multimedia Data Streams

This paper presents a framework for reasoning about the timing correctness of multimedia data streams supported on a shared, serially-reusable server. A real-time scheduling approach is used to guarantee the timing requirements for multimedia applications such as video-on-demand and multimedia presentations. This framework incorporates the use of scheduling models, which are defined as abstractions that can be used to reason about timing correctness on physical resources. The scheduling models in this paper can be applied to multimedia systems which use periodic tasks to retrieve data from a disk. With their use, the multimedia system designer can reason a priori about the throughput, capacity, and schedulability of a system. The models enable the real-time system architect to quickly explore the system design space, to establish and maintain a firm performance baseline, to optimize system configuration parameters, and to explore the impact of new technologies. As an example of the app..

Engineering and Analysis of Fixed Priority Schedulers

Scheduling theory holds great promise as a means to a priori validate timing correctness of real-time applications. However, there currently exists a wide gap between scheduling theory and its implementation in operating system kernels running on specific hardware platforms. The implementation of any particular scheduling algorithm introduces overheadand blocking components which must be accounted for in the timing correctness validation process. This paper presents a methodology for incorporating the costs of scheduler implementation within the context of fixed priority scheduling algorithms. Both event-driven and timerdriven scheduling implementations are analyzed. We show that for the timer-driven scheduling implementations the selection of the timer interrupt rate can dramatically affect the schedulability of a task set, and we present a method for determining the optimal timer rate. We analyzed both randomly generated and two well defined task sets and found that their schedulabil..

A Modeling Methodology for Real-Time/Multimedia Operating Systems

Real-time scheduling theory attempts to guarantee that a real-time task set will always meet its deadlines. Historically, there has existed a wide gap between real-time scheduling theory and the reality of applying the theory to task sets implemented via real-time operating systems (RTOSs). This paper provides a framework to account for implementation costs in real-time scheduling theory. In addition, an engineering methodology that allows users and developers to accurately model and evaluate RTOSs is presented. We use this methodology to model three different commercial real-time operating systems that are being used in multimedia applications. We show how to use the RTOS scheduling models to evaluate the performance and design of RTOSs. 1.0 Introduction Real-time scheduling theory attempts to guarantee that a set of real-time tasks can meet their timing requirements under worst case conditions [LIU73]. However, this idealized scheduling theory has generally ignored the implementati..