The Design of a Meta-System for Measurement and Simulation of Time-Sharing Computers
This report presents the results of a study of a measurement-simulation technique for evaluating modifications to time-sharing systems. The technique consists of using raw data, obtained by measurement of an operational system, as the input to a simulation model of the variant version of the system. The results of the research are reported in the form of a detailed design of a system that will perform this evaluation. It is called the Meta-System. The Meta-System consists of three parts: event-recording mechanisms in the time sharing system that record a 'system event trace', a pre-processor of the system event trace that decomposes it into independent 'task event traces' and the simulator that accepts these as input. The significant problem in the design of such a system is that of ensuring that the representations of the systems operation (the task event traces) are valid for use by the simulation model. Various solutions for the particular cases of timesharing system operation are provided in the design of each of the three stages of the Meta-System. It is shown that the Meta-System may be designed to extract representations of the time-sharing systems' operation at any one of several levels. These are called the 'levels of Meta-System awareness of system operation'. The extent of the simulation model is specified by the level, as well as the class of modifications that may be evaluated in the model. The particular Meta-System designed in this study was developed to operate with a model time-sharing system, whose features have been abstracted from those of several modern systems. These features include demand paging, multi-tasking, dynamic loading, and a virtual access method. The description of the model system is included in the report.