Towards a user-mode approach to partitioned scheduling in the seL4 microkernel

This paper presents a preliminary study of applying partitioned scheduling in the seL4 microkernel. This microkernel is the first operating system kernel ever to be formally proven for its functional correctness. Even though the kernel is completely verified it still delivers high performance comparable to other L4 kernels. The seL4 kernel implements isolation of components in terms of the memory resource and security. However, there is still a missing part when it comes to isolation and that is time partitioning. Time partitioning can be implemented inside the kernel (privileged mode) or in user space (user mode). The latter is done using regular user-space thread(s) and can easily be modified while the other approach requires re-verification of the kernel whenever modifications to the time-partitioning policy is done. On the other hand, having the time-partitioning mechanism in privileged mode would yield better performance. We have implemented time partitioning (partitioned scheduling) in the seL4 user space and we elaborate on its performance in terms of overhead costs.