CPU Service Classes for Multimedia Applications

We present the design, implementation, and experimental results of our soft real time (SRT) system for multimedia applications in a general purpose UNIX environment. The SRT system supports several service classes for the real time processes based on their processor usage time pattern: periodic constant processing time(PCPT) class, aperiodic constant processing time(ACPT) class, variable processing time (VPT) class, and one-time constant processing time(OCPT) class. It also provides the following features: (1) reservation and timing guarantees for the service classes, (2) overrun protection among real time processes, (3) dynamic earliest deadline rst (EDF) algorithm for scheduling of multiple real time (RT) processes,(4) overrun scheduling algorithm, (5) system-initiated adaptation strategies, (6) probing service to estimate the amount of processing time needed prior to a reservation, (7) pro ling service to record and retrieve the processing time needed for a reservation, (8) synchronization support among concurrent and cooperating real time processes, and (9) guaranteed allocation for traditional time sharing (TS) processes. Another unique feature of the SRT system is its easy portability to any operating systems with real time extensions because it is implemented purely in the user space without any modi cations to the kernel. We have implemented the SRT system on top of the Solaris 2.6 operating system with scheduling overhead under 400us and with good performance guarantees.