After defining the model of periodic task with multiple QoS grades for weakly hard real-time system

this paper presents DRM weakly hard real-time scheduling algorithm based on RM scheduling policy.DRM

Which has inequation for schedulablity test

not only supports task with any QoS parameter

but also changes the scheduling priority of task during scheduling to reflect its pressure.When system is overloaded

DRM can adopt QoS degradation mechanism

which enhances the flexibility of system to load by reducing service grade of tasks properly with the guarantee of important tasks scheduling with lowest QoS

so as to make more tasks running validly.At the end of this paper

simulated data is presented to show the efficiency of DRM and QoS degradation mechanism.