L8 - Scheduling Flashcards
Periodic Task
Task is released with fixed frequency and period.
Aperiodic Task.
Task has either a soft or no deadline at all. Aperiodic tasks should always be executed before periodic ones to prevent slack-stealing.
Sporadic Task
Task has hard deadline and is released at random times.
Preemtable Task
Execution of the task can be suspended.
What is the main task of a scheduler?
A scheduler allocates resources and delegates CPU to tasks.
What are key characteristics of a hard RTS?
always online; no runtime overhead; inflexible schedule
Dynamic RTS
Dynamic RTS are created at runtime.
How can scheduling performance be enhanced?
Scheduling performance can be increased by additional processors; faster computing and relaxed precedence constraints.
Describe Horn’s Algorithm/Earliest Deadline First (EDF)
The earlier the absolute deadline the higher the priority of the task. Especially for asynchronous launched tasks.
Deadline Monotonic (DM)
Priority of tasks depends on 1/ Di; can produce feasible schedule when Rate Monotonic (RM) fails.
Rate Monotonic (RM)
Priority of tasks depends on 1/ pi; always fails when Deadline Monotonic (DM) fails
Name four different dynamic scheduling algorithms.
Deadline & Rate Monotonic; Earliest-Deadline-First; Least-Slack-Time-First
What is the Least-Slack-Time-First (LSTF) algorithm? Is it a static or dynamic scheduling algorithm?
The smaller the slack time the higher the priority. Dynamic Scheduling.
What is understood as Dynamic Scheduling?
Dynamic Scheduling is priority-driven and defined at runtime.
Static Scheduling
Clock-Driven and defined at compile time.
