Section: Software and Platforms

SAS

Participants : Daniel de Rauglaudre [correspondant] , Yves Sorel.

The SAS (Simulation and Analysis of Scheduling) software allows the user to perform the schedulability analysis of periodic task systems in the monoprocessor case.

The main contribution of SAS, when compared to other commercial and academic softwares of the same kind, is that it takes into account the exact preemption cost between tasks during the schedulability analysis. Beside usual real-time constraints (precedence, strict periodicity, latency, etc.) and fixed-priority scheduling policies (Rate Monotonic, Deadline Monotonic, Audsley${}^{++}$, User priorities), SAS additionaly allows to select dynamic scheduling policy algorithms such as Earliest Deadline First (EDF). The resulting schedule is displayed as a typical Gantt chart with a transient and a permanent phase, or as a disk shape called "dameid", which clearly highlights the idle slots of the processor in the permanent phase.

For a schedulable task system under EDF, when the exact preemption cost is considered, the period of the permanent phase may be much longer than the least commun multiple (LCM) of the periods of all tasks, as often found in traditional scheduling theory. Specific effort has been made to improve display in this case. The classical utilization factor, the permanent exact utilization factor, the preemption cost in the permanent phase, and the worst response time for each task are all displayed when the system is schedulable. Response times of each task relative time can also be displayed (separately).

SAS is written in OCaML, using CAMLP5 (syntactic preprocessor) and OLIBRT (a graphic toolkit under X). Both are written by Daniel de Rauglaudre. It can be downloaded from the site http://pauillac.inria.fr/~ddr/sas-dameid/ .