Techniques for hardware virtualization have been successfully used to provide hardware-independent services and increase isolation between applications in the desktop domain. However, these characteristics make hardware virtualization also interesting for other domains like those involving control tasks.
Since these techniques were initially not conceived for this kind of environments where, in particular, timing constraints must be guaranteed, it is necessary to analyze their behavior and investigate the viability of possible solutions based on them.
In this paper, we are concerned with using VMs (Virtual Machines) to provide real-time services in the context of automotive control applications. For this purpose, we make use of the Xen hypervisor to design a real-time control loop on the top of a virtualization layer.
We first analyze a typical Xen configuration andidentify problems that arise when it is used for real-time applications. We show that the worst-case performance of Xen’s standard SEDF scheduler (Simple Earliest Deadline First) can be improved by incorporating some minimal modifications.
In addition, in order to reduce latency and jitter in a real-time control loop, we propose a new scheduler for the Xen hypervisor that uses the concept of a real-time VM. Real-time VMs are then scheduled before any other VM and under a fixed-priority policy.
Such a VM is scheduled separately with a fixed-priority scheme, which leads to a better worst-case behavior. Since the Xen hypervisor schedules multiple VMs and isolates them from one another, we can run safety-/time-critical applications (e.g., those related to airbag control and brake system ) on the same hardware with general-purpose applications (e.g., navigation and multimedia). This allows more design flexibility and supports merging multiple functionalities onto fewer processors to reduce the cost and the weight of a vehicle.
The proposed VM-based solution is shown to guarantee timing constraints typically encountered in automotive control applications.
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