Scheduling Issues Arising from Automated Real-Time System Design

We have developed CIRCA, the Cooperative Intelligent Real-time Control Architecture, as a mechanism for automating the on-line, adaptive design of real-time systems. The real-time control tasks generated by CIRCA do not meet many of the simplifying assumptions made to develop traditional scheduling algorithms. We examine several problematic issues that arise in scheduling these automatically-generated real-time monitoring tasks, and describe two solution approaches. In the rst approach, a drastic reformulation of the scheduling problem leads to a new, highly eeective scheduling algorithm, at the cost of synchronous periodic behavior in scheduled tasks. In the second approach, measured alterations are made to task periods by a band-limited search algorithm, seeking to nd nearby periods with a tractable LCM, so that traditional schedulers may be applied. We compare and contrast these approaches using experimental results from both randomly-generated task sets and task sets generated automatically by CIRCA. Our results reveal signiicant advantages for the modiied scheduling algorithm, which is based on specifying invocation separations (or \distance constraints") rather than periods. The opinions, ndings, and recommendations expressed in this publication are those of the author, and do not necessarily reeect the views of the funding agencies. David Musliner is also aaliated with the UM Institute for Systems Research (NSF Grant NSFD CDR-88003012).