Least Laxity First Llf Is A Real Time Scheduling Algorithm For Periodic Tasks

10.3. Least-laxity-first (LLF) is a real-time scheduling algorithm for periodic tasks. Slack time, or laxity, is the amount of time between when a task would complete if it started now and its next deadline. This is the size of the available scheduling window. Laxity can be expressed as

Laxity = (deadline time) − (current time) − (processor time needed)

LLF selects the task with the minimum laxity to execute next. If two or more tasks have the same minimum laxity value, they are serviced on a FCFS basis.

  1. Suppose a task currently has a laxity of t. By how long may the scheduler delay starting this task and still meet its deadline?
  2. Suppose a task currently has a laxity of 0. What does this mean?
  3. What does it mean if a task has negative laxity?