arXiv subjects

Oren Bell

Publications and source records attributed to Oren Bell.

3 recordsLinked to original sources

arXiv2025

Fixed-Priority and EDF Schedules for ROS2 Graphs on Uniprocessor

This paper addresses limitations of current scheduling methods in the Robot Operating System (ROS)2, focusing on scheduling tasks beyond simple chains and analyzing arbitrary Directed Acyclic Graphs (DAGs). While previous research has focused mostly on chain-based scheduling with ad-hoc response time analyses, we propose a novel approach using the events executor to implement fixed-job-level-priority schedulers for arbitrary ROS2 graphs on uniprocessor systems. We demonstrate that ROS 2 applications can be abstracted as forests of trees, enabling the mapping of ROS 2 applications to traditional real-time DAG task models. Our usage of the events executor requires a special implementation of the events queue and a communication middleware that supports LIFO-ordered message delivery, features not yet standard in ROS2. We show that our implementation generates the same schedules as a conventional fixed-priority DAG task scheduler, in spite of lacking access to the precedence information that usually is required. This further closes the gap between established real-time systems theory and ROS2 scheduling analyses.

cs.DC↗

arXiv2024

Bridging the Gap between ROS~2 and Classical Real-Time Scheduling for Periodic Tasks

The Robot Operating System 2 (ROS~2) is a widely used middleware that provides software libraries and tools for developing robotic systems. In these systems, tasks are scheduled by ROS~2 executors. Since the scheduling behavior of the default ROS~2 executor is inherently different from classical real-time scheduling theory, dedicated analyses or alternative executors, requiring substantial changes to ROS~2, have been required. In 2023, the events executor, which features an events queue and allows the possibility to make scheduling decisions immediately after a job completes, was introduced into ROS~2. In this paper, we show that, with only minor modifications of the events executor, a large body of research results from classical real-time scheduling theory becomes applicable. Hence, this enables analytical bounds on the worst-case response time and the end-to-end latency, outperforming bounds for the default ROS 2 executor in many scenarios. Our solution is easy to integrate into existing ROS 2 systems since it requires only minor backend modifications of the events executor, which is natively included in ROS 2. The evaluation results show that our ROS~2 events executor with minor modifications can have significant improvement in terms of dropped jobs, worst-case response time, end-to-end latency, and performance compared to the default ROS~2 executor.

cs.RO↗

arXiv2024

Host-Based Allocators for Device Memory

Memory allocation is a fairly mature field of computer science. However, we challenge a prevailing assumption in the literature over the last 50 years which, if reconsidered, necessitates a fundamental reevaluation of many classical memory management algorithms. We pose a model where the allocation algorithm runs on host memory but allocates device memory and so incur the following constraint: the allocator can't read the memory it is allocating. This means we are unable to use boundary tags, which is a concept that has been ubiquitous in nearly every allocation algorithm. In this paper, we propose alternate algorithms to work around this constraint, and discuss in general the implications of this system model.

cs.SE↗