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Earliest deadline first (EDF) or least time to go is a dynamic priority scheduling algorithm used in real-time operating systems to place processes in a priority queue. Whenever a scheduling event occurs (task finishes, new task released, etc.) the queue will be searched for the process closest to its deadline.
EEVDF was first described in the 1995 paper "Earliest Eligible Virtual Deadline First : A Flexible and Accurate Mechanism for Proportional Share Resource Allocation" by Ion Stoica and Hussein Abdel-Wahab. [2] It uses notions of virtual time, eligible time, virtual requests and virtual deadlines for determining scheduling priority. [1]
Higher schedulable utilization means higher utilization of resource and the better the algorithm. In preemptible scheduling, dynamic priority scheduling such as earliest deadline first (EDF) provides the optimal schedulable utilization of 1 in contrast to less than 0.69 with fixed priority scheduling such as rate-monotonic (RM). [1]
Earliest deadline first (EDF) or least time to go is a dynamic scheduling algorithm used in real-time operating systems to place processes in a priority queue. Whenever a scheduling event occurs (a task finishes, new task is released, etc.), the queue will be searched for the process closest to its deadline, which will be the next to be ...
Thus, during a brief overload of system resources, LST can be suboptimal. It will also be suboptimal when used with uninterruptible processes. However, like the earliest deadline first, and unlike rate monotonic scheduling, this algorithm can be used for processor utilization up to 100%.
Location of the process scheduler in a simplified structure of the Linux kernel. SCHED_DEADLINE is a CPU scheduler available in the Linux kernel since version 3.14, [1] [2] based on the earliest deadline first (EDF) and constant bandwidth server (CBS) [3] algorithms, supporting resource reservations: each task scheduled under such policy is associated with a budget Q (aka runtime), and a ...
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An RTOS that can usually or generally meet a deadline is a soft real-time OS, but if it can meet a deadline deterministically it is a hard real-time OS. [3] An RTOS has an advanced algorithm for scheduling. Scheduler flexibility enables a wider, computer-system orchestration of process priorities, but a real-time OS is more frequently dedicated ...