Flattening Hierarchical Scheduling.

ABSTRACT Recently, the application of virtual-machine technology to integrate real-time systems into a single host has received significant attention and caused controversy. Drawing two examples from mixed-criticality systems, we demonstrate that current virtualization technology, which handles guest scheduling as a black box, is incompatible with this modern scheduling discipline. However, there is a simple solution by exporting sufficient information for the host scheduler to overcome this problem. We describe the problem, the modification required on the guest and show on the example of two practical real-time operating systems how flattening the hierarchical scheduling problem resolves the issue. We conclude by showing the limitations of our technique at the current state of our research

Towards runtime monitoring in real-time systems

In this paper we present the state of our work on runtime monitoring for real-time systems: a way to observe system behavior online without unpredictably disturbing real-time properties. We discuss generic requirements to achieve these properties wherefrom we deduce our monitoring framework architecture. We describe this architecture in detail and discuss several challenges for our implementation called Ferret. We also explain why common operating system primitives, such as message passing or system calls, should not be used for monitoring in the general case and propose a very low-intrusive alternative. We also propose a way of measuring the intrusiveness caused by monitoring. We applied our technique in different scenarios ranging from simple temporal debugging, resource requirement estimation, gaining behavioral information of peripheral hardware devices to build timing models for providing real-time capable service on top of them, up to whole-system views, such as the interaction between concurrently running system threads. Our research platform also contains a para-virtualized version of Linux that we use to run legacy applications. We discuss how to apply our framework to these components with real-time requirements being only one of several important aspects. We also show how to compare the behavior of our para-virtualized Linux kernel with the behavior of the native variant. In this work, we demonstrate how to gain a continuous whole-system view by using only Ferret sensors in all layers of our system, starting from the underlying microkernel, basic microkernel programs, real-time applications, and the para-virtualized Linux kernel, as well as Linux user-space applications.