On Latency Management in Time-Shared Operating Systems

The design of general purpose operating systems impose constraints on the way one can structure real-time applications. This paper addresses the problem of minimizing the end-to-end latency of applications that are structured as a set of cooperating (real-time) tasks. When applications are structured as a set of cooperating tasks the time required for data to progress from an input task to an output task is a function of the number of the tasks that handle the data and the deadlines of individual tasks. We present an integrated inter-process communication and scheduling scheme that can be used to minimize the end-to-end latency of multi-threaded applications. Our approach is to provide the scheduler with information on the inter-process communication interconnections between tasks and to use this information to guarantee an end-to-latency to applications that is simply a function of the timing properties of the application and not its task structure. This scheme has been implemented within the YARTOS kernel and is presently being ported to the Real-Time Mach kernel.