Parametric Scheduler Characterization

Abstract

Schedulers assign starting times to events in a system such that a set of constraints is met and system productivity is maximized. We characterize the scheduler behaviour for the case where decisions are made by comparing affine expressions of design parameters such as task workload, processing speed, robot travelling speed, or a controller’s rise and settling time. Deterministic schedulers can be extended with symbolic execution, to keep track of the affine conditions on the parameters for which the scheduling decisions are made. We introduce a divide-and-conquer algorithm that uses this information to determine parameter regions for which the same sequence of decisions is taken given a particular scenario. The results provide designers insight in the impact of parameter changes on the performance of their system. The exploration can also be executed with the KLEE symbolic execution engine of the LLVM tool chain to extract the same results. We show that the divide-and-conquer approach provides the results much faster than the generic symbolic execution engine of KLEE. The results allow visualization of the sensitivity to all parameter combinations. The results of our approach therefore provide more insight in the sensitivity to parameters.