On the Feasibility of Response Time Predictions

| An Experimental Evaluation?

Alexander Vrchoticky,

Peter Puschner

Institut f?ur Technische Informatik

Technische Universit?at Wien

falex, [email protected]

January 21, 1991

Abstract

In real-time systems guarantees about the response times of tasks are of crucial importance. It has to be strictly assured, that each critical task delivers its results in time, i.e. before its deadline.

Experiments have been performed to investigate the feasibility of realistic response time predictions in practical systems, i.e. taking into account system overheads for clock synchronization, scheduling, and communication. Tasks with a simple sequential structure were executed on a state-of-the-art target system, and their execution times and response times, as well as the system overhead were measured. The observed values were then evaluated. Firstly the measured execution times of tasks and system routines were compared with computed execution times, thereby evaluating the quality of source code based execution time analysis. Secondly, we investigated the time consumption of operating system routines and DMA activities.

The results of the experiments show that response time predictions are feasible. However, in current architectures the overhead for system activities is high, thus extending the bounds unreasonably. Changes in hardware and software architectures will be a necessity for future real-time systems.

?This work has been supported in part by the ESPRIT Basic Research Project 3092 Predictably Dependable Computing Systems (PDCS)"