New schedulability analysis for MrsP

In this paper we consider a spin-based multi-processor locking protocol, named the Multiprocessor resource sharing Protocol (MrsP). MrsP adopts a helping-mechanism where the preempted resource holder can migrate. The original schedulability analysis of MrsP carries considerable pessimism as it has been developed assuming limited knowledge of the resource usage for each remote task. In this paper new MrsP schedulability analysis is developed that takes into account such knowledge to provide a less pessimistic analysis than that of the original analysis. Our experiments show that, theoretically, the new analysis offers better (at least identical) schedulability than the FIFO non-preemptive protocol, and can outperform FIFO preemptive spin locks under systems with either intensive resource contention or long critical sections. The paper also develops analysis to include the overhead of MrsP's helping mechanism. Although MrsP's helping mechanism theoretically increases schedulability, our evaluation shows that this increase may be negated when the overheads of migrations are taken into account. To mitigate this, we have modified the MrsP protocol to introduce a short non-preemptive section following migration. Our experiments demonstrate that with migration cost, MrsP may not be favourable for short critical sections but provides a better schedulability than other FIFO spin-based protocols when long critical sections are applied.