Responsive and Enforced Interrupt Handling for Real-Time System Virtualization

The increasing performance of modern processors makes virtualization a viable solution for consolidating real-time systems into a single hardware platform. Although real-time task scheduling in a virtual machine can benefit from hierarchical scheduling, unbounded interrupt handling time and vulnerability to interrupt storms make practitioners hesitant to virtualize interrupt-driven real-time applications. In this paper, we propose vINT, an interrupt handling scheme designed for real-time system virtualization. vINT provides a pseudo-VCPU abstraction dedicated for interrupt handling, which overcomes the limits imposed by the timing parameters of virtual CPUs in an analyzable way. vINT also accounts for and enforces interrupt handling and resulting execution flows within a guest virtual machine. vINT does not require any change to the guest OS code, so it can be used for virtualizing proprietary, closed-source OSs. We analyze interrupt handling time as well as VCPU and task schedulability, with and without vINT. Our experimental results indicate that vINT achieves timely interrupt handling while providing as good task schedulability as when it is not used. Our case study based on a prototype implementation on the KVM hyper visor shows that vINT yields significant benefits in reducing interrupt handling time and in protecting real-time tasks against interrupt storms permeating into the virtual machine.