ROS2 Scheduling

How does ROS schedule? Does it just use the underlying Operating System’s scheduler?

https://docs.ros.org/en/rolling/Concepts/Intermediate/About-Executors.html#scheduling-semantics

https://drops.dagstuhl.de/storage/00lipics/lipics-vol133-ecrts2019/LIPIcs.ECRTS.2019.6/LIPIcs.ECRTS.2019.6.pdf

https://discourse.ros.org/t/ros2-generated-child-thread-scheduling-policy-affects-timers/14212