Empirical Differences between COTS Middleware Scheduling Strategies Christopher D. Gill, Fred Kuhns, Douglas C. Schmidt, and Ron Cytron   View Paper (PDF)   Return to Real-Time Scheduling and Performance Abstract The proportion of complex distributed real-time embedded (DRE) systems made up of commercial-off-the-shelf (COTS) hardware and software is increasing significantly in response to the difficulty and expense of building DRE systems entirely from scratch. In previous work, we showed how applying different scheduling strategies in middleware can allow COTS-based solutions to provide both assurance and optimization of real-time constraints for important classes of mission-critical DRE systems. There are few empirical studies, however, that help developers of COTS-based DRE systems to make crucial distinctions between strategies that appear similar in policy, but whose run-time effects may differ in practice. This paper provides two contributions to the study of real-time quality of service (QoS) assurance and performance in COTS-based DRE systems. First, we examine in detail two hybrid static/dynamic scheduling strategies that should behave similarly according to policy alone, but that in fact produce different results under the same conditions, both in utilization and in meeting real-time assurances. Second, we offer recommendations based on these results for developers of mission-critical DRE systems, such as the Boeing Bold Stroke platform used in the Adaptive Software Flight Demonstration (ASFD) program under which our experiments were conducted. These contributions address and highlight the importance of the following issues to real-time scheduling in COTS environments: (1) careful mapping of scheduling policies into implementation mechanisms and (2) benchmarking and analysis of actual systems in representative operational environments. DiSC'03 © 2003 Association for Computing Machinery