Addressing cache related preemption delay in fixed priority assignment

Abstract

Handling cache related preemption delay (CRPD) in preemptive scheduling context for real-time embedded systems still stays an open issue despite of its practical importance. Indeed, classical priority assignment algorithms are only optimal when preemption costs are neglected. For example, with Audsley's Optimal Priority Assignment (OPA), as the original algorithm does not take CRPD into account, it fails frequently in identifying the schedulable task sets as it happens that the algorithm qualifies a task set to be schedulable, while it is practically not because of CRPD. In this article, we propose an approach to adapt fixed priority assignment algorithms to real-time embedded systems with cache memory. For such a purpose, we propose three extensions of the original OPA algorithm that have different degrees of pessimism, different complexities, and give different results in terms of schedulable task sets coverage. Exhaustive experimentations were achieved to evaluate the proposed approaches in terms of complexity and efficiency. The result shows that our approach provides a mean to guarantee the schedulability of the real-time embedded system while taking into account CRPD.