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Many application specific operating systems based on system on chip are composed of lots of tasks that can generate multi-tasking using preemptive scheduling. Preemptive multi-tasking incurs high preemption switching overheads, and these costs may jeopardize the system schedulability. In this paper, a novel scheduling, named dynamic preemption threshold, is proposed. The scheduling can reduce preemption costs by thread assignment and changing task dynamic preemption threshold at runtime. Because dynamic preemption threshold is based on dynamic algorithm, it can achieve higher processor utilization with relative low costs in context switching and memory requirement. The scheduling perfectly integrates preemption threshold scheduling into EDF algorithm, and accomplishes to transform static model to dynamic algorithm seamlessly.