The application of software monitor data to simulation
Authors: James O. Mulford
Venue: Proceedings of the 1st symposium on Simulation of computer systems (1973)

The use of software and hardware monitors in computer performance evaluation has increased rapidly in recent months. These tools have been able to provide much information which was previously unavailable. The application of software monitor data to simulation is one such example. A software monitor was developed at the Air Force Data Systems Design Center for the collection of data which could be used in the analysis of a new online system, the Air Force Online Data System (AFOLDS). In order to evaluate this new system, a detailed simulation analysis was conducted. Simulation models were developed using both the General Purpose Simulation System (GPSS) and the Computer Oriented Machine Evaluation Technique (COMET). These models were developed for a comparative evaluation of AFOLDS with the current Air Force online system as well as for usage in system design. The software monitor data was applied to both simulation models during various phases of the project. The software monitor was developed at the Air Force Data Systems Design Center over a period of four months. This development included definition of statistics to be gathered, programming, testing, and modification, as necessary. The definition of statistics was initially based on the needs dictated by the AFOLDS simulation. A monitor was needed which could collect timings on various MCP (Master Control Program - B5500 operating system) routines and online functions. In general, the three areas monitored were MCP overlay usage, Input/Output (I/O) control usage, and usage of predefined checkpoints within the MCP. The COMET simulations were used in evaluating the impact of AFOLDS on the entire online session. The average changes in response times, processing times, and message capacity were evaluated with these simulations. Software monitor data was used in defining processing ratios, I/O peripheral usage, and MCP overhead time costs. It was also used in the validation of the model as well as some of its' results. The GPSS simulations were used in the analysis o f queue stability, growth potential, and peak period processing during the on line session. This analysis involved a detailed simulation of a small portion of the online session. The software monitor was able to provide detailed timings, arrival rates, and queue lengths for this model. Flowcharts of the MCP and on line programs along with queueing theory techniques were used in the development of a valid model. The software monitor data was then used to provide the needed timing and queueing characteristics of the model. This monitored data was also used during all phases of the GPSS simulation model validation. The software monitor data was a necessary element of the simulation analysis of the Air Force Online Data System. It was this collected data which provided the required timings and message rates needed for a valid simulation. Not only could a more detailed model be developed with these accurate timings, but many approximations could be replaced by actual computer characteristics. The added model confidence provided through the use of monitor data gives this tool a definite place in the computer simulation process.