System virtualization's integration of multiple software stacks with maintained isolation on multi-core architectures has the potential to meet high functionality and reliability requirements in a resource efficient manner. Paravirtualization is the prevailing approach in the embedded domain. Its applicability is however limited, since not all operating systems can be ported to the paravirtualization application programming interface. Proteus is a multi-core hypervisor for PowerPCbased embedded systems, which supports both full virtualization and paravirtualization without relying on special hardware support. The hypervisor ensures spatial and temporal separation of the guest systems. The evaluation indicates a low memory footprint of 15 kilobytes and the configurability allows for an application-specific inclusion of components. The interrupt latencies and the execution times for hypercall handlers, emulation routines, and virtual machine context switches are analyzed.
Virtualization's architectural abstraction and encapsulation of guest systems in virtual machines facilitate migration, but existing real-time virtualization solutions are characterized by a static mapping of virtual machines to processors. This work studies migration of virtual machines with realtime constraints on homogeneous multiprocessor architectures as a service restoration in response to hardware faults. The migration policy respects real-time requirements and minimizes and predicts deadline misses based on a preceding comparison of downtime caused by the migration and slack-based computation of the virtual machine's maximum affordable downtime. The distributed design is characterized by a communication between the paravirtualized operating system and the hypervisor in order to provide the required scheduling information. The overhead regarding memory footprint, execution times, and paravirtualization effort is analyzed. The evaluation identifies ranges for virtual machine size and timing characteristics for which the approach is feasible. A reliability analysis based on a combinatorial model is used to quantify the impact of migration on reliability.
System virtualization is a powerful approach for the creation of integrated systems, which meet the high functionality and reliability requirements of complex embedded applications. It is in particular well-suited for mixed-criticality systems, since the often applied pessimistic manner of critical system engineering leads to heavily under-utilized resources. Existing static resource management approaches for virtualized systems are inappropriate for the dynamically varying resource requirements of upcoming adaptive systems. In this paper, we propose a dynamic resource management protocol for system virtualization that factors criticality levels in and allows the addition of subsystems at runtime. The two-level architecture offers flexibility across virtual machine borders and has the potential to improve the resource utilization. In addition, it provides the capability to adapt at runtime according to defects or changes of the environment.
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