Deadlines and urgency

A deadline is a soft "should be done by" time. It does not cancel the task when it passes; it raises the task's score as the deadline approaches so that it is dispatched in time.

Latest start time

d   = duration estimate (duration_hint, else learned median for (pool, kind),
      else the pool's learned median, else the pool's default_duration = 1 s)
LST = deadline − d          latest start time
slack = LST − now
H   = max(d, urgency_window)            urgency_window = 5 s

Urgency curve

urgency = 0                                      if slack ≥ H
        = U × (1 − slack / H)                    if 0 ≤ slack < H
        = U + min(overdue_rate × (−slack), cap)  if slack < 0

with U = 5000, overdue_rate = 100 per second and cap = 3000.

 urgency
 8000 ┤                                  ┌──────────── cap reached
      │                               ╱
 5000 ┤                        ●───╱       overdue: keeps rising
      │                     ╱
      │                  ╱      rising linearly over the horizon H
    0 ┼───────────────╱
      └──────────────┬──────────┬──────────────────▶ time
                  LST − H      LST

The curve is monotonic: a task that is further past its latest start always has at least the urgency of one that is less late.

Ordering

• Within a class, tasks with deadlines are kept in a queue ordered by latest start time (earliest-deadline-first), and the head competes with the class's FIFO lane by full score.
• Across classes, urgency is added to the base score, so a Low task near its deadline (10 + 5000) overtakes fresh High work (1000) but not Critical work (10000).

Choosing values

• Give a duration_hint when you know it; otherwise the first tasks of a kind use the pool's learned typical run time (or default_duration if nothing in the pool has completed yet) until cronoq has observed completions of that kind.
• Deadlines are about finishing. If something must start at a given time, use a fixed start.
• To get more capacity when deadlines are at risk, set per-class wait SLOs in the pool's autoscaling configuration.

Configuration