A real-time monitor is employed to aid in scheduling tasks with random execution times in a real-time computing system. The real-time monitor is composed of dedicated hardware called test and measurement processors (TMPs). It is used to measure accurately and with minimal interference the true execution time, which consists of pure execution time and resource sharing delay. The monitor is a permanent and transparent part of a real-time system. It degrades system performance by less than 0.1% and does not interfere with the host system's execution. The measured pure execution time and resource sharing delay for each task have been used to develop a mechanism that reduces the discrepancy between the worst-case execution time (WET) and the estimated execution time. This result is used to decide at the earliest possible time whether or not a task can meet its deadline. A set of example tasks are experimentally measured in a simulated environment while their characteristics are varied. The measured data are analyzed, demonstrating the utility and power of the proposed real-time monitor.>

The authors describe a hybrid monitor for measuring the performance and observing the behavior of distributed systems during execution. They emphasize data collection, analysis and presentation of execution data. A special hardware support, which consists of a test and measurement processor (TMP), was designed and has been implemented in the nodes of experimental multicomputer system consisting of eleven nodes. The operations of the TMP are completely transparent with a minimal, less than 0.1%, overhead to the measured system. In the experimental system, all the TMPs were connected with a central monitoring station, using an independent communication network, in order to provide a global view of the monitored system. The central monitoring station displayed the resulting information in easy-to-read charts and graphs. Experience with the TMP shows that it promotes an improved understanding of run-time behavior and performance measurements, which aids in deriving qualitative and quantitative assessments of distributed systems.>

A real-time monitor is employed to aid in scheduling tasks with random execution times in a real-time computing system. Scheduling algorithms are usually based on the worst-case execution time (WET) of each task. Due to data-dependent loops and conditional branches in each program and resource-sharing delay during execution, this WET is usually difficult to obtain and could be several orders of magnitude larger than the true execution time. Thus, scheduling tasks based on WET could result in a severe underutilization of CPU cycles and underestimation of the system's schedulability. To alleviate this problem, a real-time monitor is proposed for use as a scheduling aid. The real-time monitor is composed of dedicated hardware, called test and measurement processors (TMPs), used to measure with minimal interference the true execution time, which consists of the pure execution time and resource-sharing delay. The monitor, a permanent and transparent part of a real-time system, degrades system performance by less than 0.1% and does not interfere with the host system's execution. Using the measured pure execution time and resource-sharing delay for each task, a mechanism which reduces the discrepancy between the WET and the estimated execution time has been developed. This result is then used to decide at the earliest possible time whether a task can meet its deadline.>

This paper describes an integrated tool for monitoring distributed systems continuously during operation. A hybrid monitoring approach is used. As special hardware support a test and measurement processor (TMP) was designed, which is part of each node in an experimental multicomputer system. Each TMP runs local parts of the monitoring software for its node, while all the TMPs are connected to a central test station via a separate TMP interconnection network. The monitoring system is transparent to users. It permanently observes system behavior, measures system performance and records system information. The immense amount of information is graphically displayed in easy-to-read-charts and graphs in an application-oriented manner. The tools promote an improved understanding of run time behavior and performance measurements to derive qualitative and even quantitative assessments about distributed systems. A prototype of the monitoring facility is operational and currently experiments are being conducted in our distributed system consisting of several MC68000 microcomputers.

This paper gives an overview of the INCAS (INCremental Architecture for distributed Systems) multicomputer project, which aims at the development of a comprehensive methodology for the design and implementation of locally distributed systems. A structuring concept for distributed operating systems has been developed and integrated into the system implementation language LADY. The concurrent high-level programming language CSSA, based on the actor model, has been designed for the implementation of distributed applications. A substantial effort in the INCAS project is directed towards the development of a distributed test methodology. An experimental system has been implemented on a network of ten MC68000 microcomputers. Preliminary experience with the methodology has been gained from a small number of prototype applications.