Deadline Scheduler (DL)

struct sched_dl_entity

Deadline Scheduling Class (SCHED_DEADLINE) defined in
kernel/sched/deadline.c.

It implements a real-time scheduling policy based on:

• Earliest Deadline First (EDF) scheduling
• Constant Bandwidth Server (CBS) for bandwidth enforcement

SCHED_DEADLINE is designed for tasks with explicit timing constraints, commonly used in real-time systems where tasks must complete before a deadline.

Key Parameters

Each SCHED_DEADLINE task defines three parameters:

• Runtime (runtime) – maximum execution time allowed
• Deadline (deadline) – time by which the job must finish
• Period (period) – activation interval of the task

These parameters define the scheduling contract:

runtime <= deadline <= period

Scheduling Policy

The scheduler maintains a runqueue ordered by absolute deadlines.

The task with the earliest deadline is selected to run first, implementing the EDF scheduling algorithm.

If a task exceeds its allocated runtime, the CBS mechanism throttles the task to ensure it does not consume more CPU bandwidth than allowed.

Admission Control

Before admitting a new SCHED_DEADLINE task, the kernel checks that total CPU utilization does not exceed the schedulable bound.

For a single CPU:

Σ (runtime / period) ≤ 1

If the constraint is violated, the task is rejected.

Typical Use Cases

• Real-time multimedia processing
• Robotics and control systems
• Industrial real-time applications
• Deterministic embedded workloads

SCHED_DEADLINE provides strong temporal guarantees, making it suitable for systems where meeting deadlines is critical.