Deadline Monotonic Scheduling

Deadline Monotonic Scheduling ( DMS) referred to in the computer science a scheduling method for hard real- time systems, which is used to manage processes fixed priorities. Among the scheduling method with fixed priorities, it is optimal for arbitrary deadlines.

Assumptions

Basic restrictions

The theoretical analysis of real-time scheduling method requires some basic constraints, in order to handle the complexity of the analysis.

• Processes can be interrupted at any time
• The overhead for process change is accepted with 0 time units
• Necessary resources (other than CPU time ) are available in unlimited amounts
• All processes are independent ( intuitively: The processes can be performed in any order )
• The burden of all processes together must be ≤ 1

Assumptions for periodic processes

• All processes have deadlines less than or equal to their periods

Assumptions for sporadic processes

• All processes have deadlines less than or equal to its minimum inter -arrival times ( minimum between two arrivals of the same process )

Method

Analogous to rate monotonic scheduling (RMS ) is performed at DMS always the process of highest priority. The priorities are thereby assigned the reciprocal of the relative period length. The method is preemptively - when a new process with a higher priority of the current process is interrupted in favor of the new. To be able to handle aperiodic jobs, a fictitious periodic process is assumed to be the minimum inter -arrival time as the period for this.

Cardinality

DMS is the most powerful method under the scheduling method with fixed priorities. It is a generalization of rate monotonic scheduling, with RMS with only one scheduling a subset of executable with DMS process quantities is possible. In the special case that relative deadline and period lengths are the same for all processes, DMS applies = RMS.