Hierarchical scheduling of real-time tasks over Linux-based virtual machines

Virtualization has made feasible the full isolation of virtual machines (VMs) among each other. When applications running within VMs have real-time constraints, threads implementing the virtual cores must be scheduled in a predictable manner over the physical cores. In this paper, we propose a possible implementation of such a predictable VM scheduling based on Linux and kvm (a hosted hypervisor). The proposed implementation is based on vanilla Linux kernels and standard qemu/kvm, and does not require to apply any patch or to use custom software. We also show that previous work makes some assumptions that are unrealistic in practical situations. Motivated by these considerations, we finally propose a principled methodology to practically implement hierarchical scheduling with Linux. Finally, an extensive set of experiments based on Linux and kvm illustrates how the VMs and host scheduler can be set-up to match theoretical results with experiments.