The most well-known DPS is the earliest deadline first (EDF) scheduling policy []. Using EDF, the task with the nearest (earliest) deadline among all tasks ready for execution gets the highest priority.
Therefore, the priority is not fixed; it changes dynamically over time.
Schedulability is in the simple scenario guaranteed as long as the total load in the scheduled system is ≤%, whereas a FPS in these simple cases has a schedulability bound of about %.
For a good comparison between RM and EDF interested readers are referred to [].