Admission Control for Independently-authored Realtime Applications

This thesis presents the LiquiMedia operating system architecture. LiquiMedia is specialized to schedule multimedia applications. Because they generate output for a human observer, multimedia applications such as video games, video conferencing and video players have both unique scheduling requirements and unique allowances: a multimedia stream must synchronize sub-streams generated for different sensory modalities within 20 milliseconds, it is not successfully segregated until it has existed for over 200 milliseconds and tolerates occasional scheduling failures. LiquiMedia is specialized around these requirements and allowances. First, LiquiMedia synchronizes multimedia tasks by invoking them from a shared realtime timer interrupt. Second, owing to multimedia’s tolerance of scheduling failures, LiquiMedia schedules tasks based on a probabilistic model of their running times. Third, LiquiMedia can infer per-task models while a user is segregating the streams that the tasks generate. These specializations provide novel capabilities: up to 2.5 times higher utilization than RMS scheduling, use of an atomic task primitive 9.5 times more efficient than preemptive threading, and most importantly, the ability to schedule arbitrary tasks to a known probability of realtime execution without a priori knowledge of their running times.