Paravirtualizing Linux in a real-time hypervisor

International audienceThis paper describes a new hypervisor built to run Linux in a virtual machine. This hypervisor is built inside Anaxagoros, a real-time microkernel designed to execute safely hard real-time and non real-time tasks. This allows the execution of hard real-time tasks in parallel with Linux virtual machines without interfering with the execution of the real-time tasks. We implemented this hypervisor and compared performances with other virtualization techniques. Our hypervisor does not yet provide high performance but gives correct results and we believe the design is solid enough to guarantee solid performances with its future implementation

Real time control in Linux

In this thesis, the approaches to achieving real time control under Linux operating platform are presented and four different real time control applications are discussed. The driver of the ADS 12 data acquisition card is programmed to enhance hardware supported by COMEDI through which the connection between computer and DAQ boards are built up. A simple project combining RTAI (Real Time Application Interface) with COMEDI is introduced together with the discussion of one SISO (Single-Input Single-Output) control project and two SIMO (Single-Inputs Multi- Output) control projects based on different controllers, and RTLab is selected to provide us with real time functionalities as it combines COMEDI with RTAI or RTLinx very well in Linux. Further more, to enhance the observability and maneuverability of RTLab, additional custom plugin graphic windows have also been made for every application in the project

Hard Real-Time Networking on Firewire

This paper investigates the possibility of using standard, low-cost, widely used FireWire as a new generation fieldbus medium for real-time distributed control applications. A real-time software subsystem, RT-FireWire was designed that can, in combination with Linux-based real-time operating system, provide hard real-time communication over FireWire. In addition, a high-level module that can emulate Ethernet over RT-FireWire was implemented. This additional module enables existing IP-based real-time communication frameworks to work on top of FireWire. The real-time behavior of RT-FireWire was demonstrated with a simple control setup. Furthermore, an outlook of the future development on RT-FireWire is given

Challenges Using Linux as a Real-Time Operating System

Human-in-the-loop (HITL) simulation groups at NASA and the Air Force Research Lab have been using Linux as a real-time operating system (RTOS) for over a decade. More recently, SpaceX has revealed that it is using Linux as an RTOS for its Falcon launch vehicles and Dragon capsules. As Linux makes its way from ground facilities to flight critical systems, it is necessary to recognize that the real-time capabilities in Linux are cobbled onto a kernel architecture designed for general purpose computing. The Linux kernel contain numerous design decisions that favor throughput over determinism and latency. These decisions often require workarounds in the application or customization of the kernel to restore a high probability that Linux will achieve deadlines

Towards an HLA Run-time Infrastructure with Hard Real-time Capabilities

Our work takes place in the context of the HLA standard and its application in real-time systems context. The HLA standard is inadequate for taking into consideration the different constraints involved in real-time computer systems. Many works have been invested in order to providing real-time capabilities to Run Time Infrastructures (RTI) to run real time simulation. Most of these initiatives focus on major issues including QoS guarantee, Worst Case Transit Time (WCTT) knowledge and scheduling services provided by the underlying operating systems. Even if our ultimate objective is to achieve real-time capabilities for distributed HLA federations executions, this paper describes a preliminary work focusing on achieving hard real-time properties for HLA federations running on a single computer under Linux operating systems. Our paper proposes a novel global bottom up approach for designing real-time Run time Infrastructures and a formal model for validation of uni processor to (then) distributed real-time simulation with CERTI

Real-time capabilities in the standard Linux Kernel: How to enable and use them?

Linux was originally designed as a general purpose operating system without consideration for real-time applications. Recently, it has become more attractive to the real-time community due to its low cost and open source approach. In order to help the real-time community, we will present in this paper the practical steps required to achieve a real-time Linux by applying the PREEMPT-RT patches which will provide Linux with these capabilities. We will also focus on some of the kernel configuration that should get attention while building the kernel in order to maintain the real-time behavior of the system during runtime. DOI: 10.17762/ijritcc2321-8169.15012

Lachesis: a testsuite for Linux based real-time systems

none2Testing is a key step in software development cycle. Error and bug fixing costs can easily exceed development costs without a full and comprehensive test on the system. First efforts to introduce real-time features in the Linux kernel are now more than ten years old. Nevertheless, no comprehensive testsuites is able to assess the functionality or the conformance to the real-time operating systems standards of the Linux kernel and of real-time nanokernels that rely on it. In this paper we propose Lachesis, an automated testsuite derived from the LTP (Linux Test Project) real-time tests. Lachesis main goals are: to provide extensive and comprehensive testing of real-time Linux features; to provide a set of functional, regression, performance and stress test, either developing or porting them from other testsuites; to design and experiment a series of build tests; to minimize development time for new tests; to make the testsuite extensible and portable. Lachesis can be used to test Linux, PREEMPT_RT, RTAI and Xenomai real-time features and performances. It provides some tests for SCHED_DEADLINE patch, too. Lachesis is now under active development: extensions to other real-time systems and more tests are planned to be added in the near future.A. Claudi; A. F. DragoniClaudi, Andrea; Dragoni, Aldo Franc

Joint Time-and Event-Triggered Scheduling in the Linux Kernel

There is increasing interest in using Linux in the real-time domain due to the emergence of cloud and edge computing, the need to decrease costs, and the growing number of complex functional and non-functional requirements of real-time applications. Linux presents a valuable opportunity as it has rich hardware support, an open-source development model, a well-established programming environment, and avoids vendor lock-in. Although Linux was initially developed as a general-purpose operating system, some real-time capabilities have been added to the kernel over many years to increase its predictability and reduce its scheduling latency. Unfortunately, Linux currently has no support for time-triggered (TT) scheduling, which is widely used in the safety-critical domain for its determinism, low run-time scheduling latency, and strong isolation properties. We present an enhancement of the Linux scheduler as a new low-overhead TT scheduling class to support offline table-driven scheduling of tasks on multicore Linux nodes. Inspired by the Slot shifting algorithm, we complement the new scheduling class with a low overhead slot shifting manager running on a non-time-triggered core to provide guaranteed execution time to real-time aperiodic tasks by using the slack of the time-triggered tasks and avoiding high-overhead table regeneration for adding new periodic tasks. Furthermore, we evaluate our implementation on server-grade hardware with Intel Xeon Scalable Processor.Comment: to appear in Operating Systems Platforms for Embedded Real-Time applications (OSPERT) workshop 2023 co-hosted with 35th Euromicro conference on Real-time system