Queue-based scheduling for soft real time applications

Modern multitasking multimedia streaming applications impose tight timing requirements that demand specific scheduling policies. General purpose operating systems such as Linux (widely diffused even in embedded systems) are not specifically designed for such applications as they must ensure an overall performance level for a wide range of user processes. Realtime versions of general purpose kernels can be used, however since they are designed for hard real-time applications, they impose explicit knowledge of deadlines for all tasks composing the application to set their priorities. In this work a novel streaming-oriented scheduling algorithm is proposed, that relies on a standard interprocess communication support for applications composed by multiple pipelined stages communicating by means of message queues. It determines the scheduling order depending on the queue occupancy, for this reason does not require explicit deadline information. It has been developed in Linux OS as a new real time policy, showing that it is relatively easy to integrate in it and, worthily, it does not require modifications of existing applications.