Ros ${ }^{\text {RT }}$: Enabling Flexible Scheduling in Ros 2

The Robot Operating System 2 (ROS) is heavily used in autonomous systems due to its large ecosystem and modular design. However, ROS remains problematic for real-time applications despite prior efforts to improve its real-time capabilities. Many of these problems are rooted in the implementation of the ROS executor, which does not support preemption or userspecified priorities. These properties are fundamental to real-time scheduling and desirable for general systems to reduce latency. ROS variants in prior work have separately supported the preemption and prioritization of callbacks but place restrictions on the application, preventing their adoption in a real-world workload. This paper addresses these deficiencies with a novel executor framework,$\operatorname{ROS}^{\text{RT}}$, which is compatible with any type of ROS application while supporting preemptive, priority-driven scheduling. Additionally, to support flexible EDF scheduling in ROS${ }^{\text {RT }}$, a custom EDF scheduler implementation is proposed using the new Linux scheduling class SCHED_EXT. ROS${ }^{\text {RT }}$s flexibility and real-time compatibility do not come at the cost of overheads: it achieves a significant decrease in publisher-tosubscriber overhead from the native ROS executor. Finally, this paper concludes with a case study performed on the Autoware Reference System, which simulates the execution of the LiDAR module in an autonomous driving application, demonstrating the ability of$\operatorname{ROS}^{\text{RT}}$at real-time scheduling in real-world scenarios.