PiCAS for ROS2 Galactic

1. Implementation of Priority-Driven Chain-Aware scheduling

Setup

• This repository includes the PICAS-enabled rclcpp package and some example code that tests PICAS APIs.
• Before building this repo, make sure that your system has ROS 2 packages installed on it (see this link for ROS 2 installation).
• Build repo with PICAS support enabled

  source /opt/ros/galactic/setup.bash
  colcon build --allow-overriding rclcpp --cmake-args -DPICAS=TRUE
  

• Build repo without PICAS (default rclcpp)

  source /opt/ros/galactic/setup.bash
  colcon build --cmake-args -DPICAS=FALSE
  

How to use API

• Please see the example code in ros2-picas-example > picas_example > src > example.cpp for a single-threaded executor, and ros2-picas-example > picas_example_mt > src > example_mt.cpp for a multi-threaded executor
• Create executor and callbacks, e.g., timer_callback, regular_callback, exec1

  auto timer_callback = std::make_shared<StartNode>("callback_name", "pub_topic_name", trace_callbacks, exe_time(msec), period(msec), false);
  auto regular_callback = std::make_shared<IntermediateNode>("callback_name", "sub_topic_name", "pub_topic_name", trace_callbacks, exe_time(msec), true);
  

Then,

  rclcpp::executors::SingleThreadedExecutor exec1; // single-threaded executor
  

or

  rclcpp::executors::MultiThreadedExecutor exec1; // multi-threaded executor
  

• sub_topic_name: the name of subscription topic
• pub_topic_name: the name of publishing topic
• exe_time: execution time of callback in msec
• period: period of timer callback in msec

• trace_callbacks: print time stamp as a txt file (see ros2-picas-example > trace_picas)

• Enable priority-based scheduling

  exec1.enable_callback_priority();
  

• Set executor’s rt priority (SCHED_FIFO in linux) and CPU assignment
  • For single-threaded executors:

  exec1.set_executor_priority_cpu(90, 5); // (90: rt priority, 5: cpu #)
  

• For multi-threaded executors:

  exec1.cpus = {1, 2, 3}; // CPU1, 2, 3
  exec1.rt_attr.sched_priority = SCHED_FIFO;
  exec1.rt_attr.sched_priority = 80;
  

Other policies such as SCHED_RR and SCHED_DEADLINE are also usable.

• Set priority of callback

  exec1.set_callback_priority(timer_callback->timer_, 10); // 10: callback's priority (the higher, more critical callback)
  

• Finally, spin
  • Single-threaded executor: use spin_rt for real-time priority in linux

  std::thread spinThread1(&rclcpp::executors::SingleThreadedExecutor::spin_rt, &exec1);
  

• Multi-threaded executor: spin assigns each thread’s rt priority and cpu affinity based on prespecified params.

  exec1.spin();
  

Run example

• Use sudo authority when running ros2 package to leverage rt priority in linux system.
  • Modify /etc/security/limits.conf as below then reboot the system

  <userid>  hard    rtprio  99
  <userid>  soft    rtprio  99

• Run example

  source install/setup.bash
  ./build/picas_example/example   # single-threaded version

  ./build/picas_example_mt/example_mt   # multi-threaded version

NOTE: Please reference our ROS2-PiCAS paper that was published in RTAS 2021.

@inproceedings{choi2021picas,
  title={PiCAS: New Design of Priority-Driven Chain-Aware Scheduling for ROS2},
  author={Choi, Hyunjong and Xiang, Yecheng and Kim, Hyoseung},
  booktitle={2021 IEEE 27th Real-Time and Embedded Technology and Applications Symposium (RTAS)},
  pages={251--263},
  year={2021},
  organization={IEEE}
}