Real-time scheduling support in Ultrix-4.2 for multimedia communication

Abstract

Advanced workstations are now being equipped to handle various types of multimedia applications such as audio and video. The quality of these images and sounds depends highly on the timely management of multimedia data. In order to provide such management, support for real-time process scheduling must exist. In this paper we describe the fundamental mechanisms implemented in the Ultrix4.2 kernel that provide the real-time scheduling support needed for multimedia applications. Our primary goal is to reduce and bound the overall delay in the response times to both internal as well as external events. To achieve this goal we have modified the Ultrix4.2 kernel to be preemptible at highly specific locations and have added a small subset of data structure locks to maintain data consistency. Work has also been done towards reducing and bounding the time spent resolving lock conflicts. The end result is that we have a kernel capable of the real-time processing necessary for multimedia applications. Finally, we demonstrate and validate through experimentation that the above claim is true.

This research was supported by the National Science Foundation and the Defense Advanced Research Projects Agency (DARPA) under Cooperative Agreement NCR-8919038 with the Corporation for National Research Initiatives, by AT&T Bell Laboratories, Hitachi, Ltd., Hitachi America, Ltd., Pacific Bell, the University of California under a MICRO grant, and the International Computer Science Institute. The views and conclusions contained in this document are those of the authors, and should not be interpreted as representing official policies, either expressed or implied, of the U.S. Government or any of the sponsoring organizations.