RAPLET: Demystifying Publish/Subscribe Latency for ROS Applications

The problem of real-time scheduling based on the Directed Acyclic Graph (DAG) task model has been extensively studied in the literature. Most of the studies are aimed at the development of efficient scheduling algorithms to reduce deadline misses and/or improve schedulability bounds on the given task system. In order to guarantee real-time performance of the DAG task model in practice, the latency imposed on the communication between the DAG nodes must be systematically taken into account. This paper aims at demystifying the latency of the Robot Operating System (ROS) as a practical DAG task model, which leverages the publish/subscribe mechanism to send and receive data between the nodes. To this end we present the ROS-Aware Publish/Subscribe Latency Evaluation Tool (RAPLET) which is designed to measure and visualize the details of the publish/subscribe latency in ROS. RAPLET consists of (i) the LD PRELOAD scheme that inserts function hooks in user-land and (ii) the extended Berkeley Packet Filter (eBPF) scheme that monitors the run-queue level and the network states in kernel-land. The performance analysis on ROS applications, including a real-world autonomous driving software, is performed using RAPLET to demonstrate that the publish/subscribe latency imposed on inter-node communication can be demystified and reasoned with respect to system issues including the message size and network bandwidth consumption.