Modeling and validation of the real-time Mach scheduler

Abstract

Real-time scheduling theory is designed to provide a priori verification that all real-time tasks meet their timing requirements. However, this body of theory generally assumes that resources are instantaneously pre-emptable and ignores the costs of systems services. In previous work [1, 2] we provided a theoretical foundation for including the costs of the operating system scheduler in the real-time scheduling framework. In this paper, we apply that theory to the Real-Time (RT) Mach scheduler. We describe a methodology for measuring the components of the RT Mach scheduler in user space. We analyze the predicted performance of different real-time task sets on the target system using the scheduling model and the measured characteristics. We then verify the model experimentally by measuring the performance of the real-time task sets, consisting of RT Mach threads, on the target system, The experimental measurements verify the analytical model to within a small percentage of error. Thus, using the model we have successfully predicted the performance of real-time task sets using system services, and developed consistent methodologies to accomplish that prediction.