Application of real-time monitoring to scheduling tasks with random execution times

A real-time monitor is employed to aid in scheduling tasks with random execution times in a real-time computing system. The real-time monitor is composed of dedicated hardware called test and measurement processors (TMPs). It is used to measure accurately and with minimal interference the true execution time, which consists of pure execution time and resource sharing delay. The monitor is a permanent and transparent part of a real-time system. It degrades system performance by less than 0.1% and does not interfere with the host system´s execution. The measured pure execution time and resource sharing delay for each task have been used to develop a mechanism that reduces the discrepancy between the worst-case execution time (WET) and the estimated execution time. This result is used to decide at the earliest possible time whether or not a task can meet its deadline. A set of example tasks are experimentally measured in a simulated environment while their characteristics are varied. The measured data are analyzed, demonstrating the utility and power of the proposed real-time monitor