Multi Sloth: An Efficient Multi-core RTOS Using Hardware-Based Scheduling

Multi-core operating systems inherently face the problem of concurrent access to internal kernel state held in shared memory. Previous work on the Sloth real-time kernel proposed to offload the scheduling decisions to the interrupt hardware, thus removing the need for a software scheduler, no state has to be managed in software. While our existing design covers single-core platforms only, we now present Multi Sloth, a multi-core AUTOSAR OS implementation. In this paper, we show that our hardware-centric approach enables us to easily make the transition to multi-core platforms without the need for explicitly synchronizing kernel data. Even in the case of cross-core interactions, Multi Sloth keeps the unique Sloth properties of strict priority obedience and complete prevention of rate-monotonic priority inversions. AUTOSAR OS mandates only unordered spin locks, which do not guarantee predictable timing. We show the advantages of the Multi Sloth design by additionally providing a wait-free and efficient implementation of the priority-aware Multiprocessor Priority Ceiling Protocol (MPCP). On our reference platform, we achieve overheads as low as 1.1 μs for acquiring a globally shared resource using the MPCP and round-trip times of 1.4 μs for cross-core task activations.