Evaluating MSRP and MrsP with the Multiprocessor Ravenscar Profile

One of the main challenges of developing real-time systems with Ada on multiprocessor platforms is finding an appropriate scheduling policy and locking policy for shared objects. Some modifications of the standard Ceiling_Locking policy have been proposed for multiprocessor architectures, among which MSRP and MrsP have raised most interest. In this paper the possible uses of both policies in full Ada and Ravenscar programs are explored. To this purpose, classical response time analysis is extended in the paper to deal with heterogeneous access costs in multiprocessor systems. A case study has been used to validate the approach, and an extensive test bench for comparing MSRP and MrsP has been run in order to compare the schedulability properties of both methods. The conclusion is that, although MrsP provides a better overall performance, in many practical situations the simpler MSRP protocol provides comparable results when considering heterogeneous access costs, while being compatible with the Ravenscar restrictions.