An hour-long deep dive into the details of Zephyr's evolving thread scheduling facilities, their interactions with the broader OS and their application (and misapplication) to real systems. Topics include a quick overview of the base priority-based scheduler, what "cooperative" priorities really mean, how MetaIRQ priorities work and what they are for, Earliest-Deadline-First priorities, and the new p4workq abstraction for matching pooled threads with scheduler parameters.