Section: New Results

Dependable Distributed Real-time Embedded Systems

Participants : Gwenaël Delaval, Pascal Fradet, Alain Girault [contact person] , Emil Dumitrescu.

Tradeoff exploration between reliability, power consumption, and execution time

For autonomous critical real-time embedded systems (e.g., satellite), guaranteeing a very high level of reliability is as important as keeping the power consumption as low as possible. We have designed an off-line ready list scheduling heuristics which, from a given software application graph and a given multiprocessor architecture (homogeneous and fully connected), produces a static multiprocessor schedule that optimizes three criteria: its length (crucial for real-time systems), its reliability (crucial for dependable systems), and its power consumption (crucial for autonomous systems). Our tricriteria scheduling heuristics, TSH, uses the active replication of the operations and the data-dependencies to increase the reliability, and uses dynamic voltage and frequency scaling to lower the power consumption [17] , [11] . By running TSH on a single problem instance, we are able to provide the Pareto front for this instance in 3D, therefore exposing the user to several tradeoffs between the power consumption, the reliability and the execution time. The new contribution for 2012 has been the formulation of a new multi-criteria cost function for our ready list scheduling heuristics, such that we are able to prove rigorously that the static schedules we generate meet both the reliability constraint and the power consumption constraint.

Thanks to extensive simulation results, we have shown how TSH behaves in practice. Firstly, we have compared TSH versus an optimal Mixed Linear Integer Program on small instances; the experimental results show that TSH behaves very well compared to the the ILP. Secondly, we have compared TSH versus the ECS heuristic (Energy-Conscious Scheduling [68] ); the experimental results show that TSH performs systematically better than ECS.

This is a joint work with Ismail Assayad (U. Casablanca, Morocco) and Hamoudi Kalla (U. Batna, Algeria), who both visit the team regularly.