Editorial: Resource allocation in Real-Time Systems

Abstract

Large real-time systems are complex. In these systems there are usually many periodic and aperiodic tasks, a high degree of concurrency, and significant asynchronous behavior. Requirements often demand careful design and analysis so that the system is predictable. Unfortunately, much of the analysis has focused on a too simplistic model. For example, the basic rate monotonic result requires many simplistic assumptions which are not met in practice. Consequently, for a complex system it does not matter that you have a beautiful theorem with precise analysis because the coverage of the assumptions compared to the real system is low. While the basic approach may still be useful for an approximate analysis, it must be noted that any approximate analysis is more limited for a real-time system than for a general purpose timesharing system because designers require precise analysis with respect to deadlines of specific tasks. Another example of simplistic analysis is earliest deadline scheduling. Simple formulas can again provide precise results based on assumptions such as all tasks are preemptable at any point, there is no sharing of resources, and no overloads will ever exist. Again, if the manner in which these assumptions match the real system is poor then the precise analysis is not precise at all for the system in question! One key problem with the basic rate monotonic and earliest deadline policies and their analyses is that they fail to recognize that all resources must be addressed by the analysis and not just the CPU. In other words, what is required is an integrated resource allocation model for real-time where