realtime:documentation:technical_basics:sched_policy_prio
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| - | ====== Scheduling - Policy and Priority ====== | ||
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| - | Depending on the chosen task policy and associated rules the scheduler | ||
| - | decides which task is swapped out and which task is processed | ||
| - | next. The Linux kernel implements several scheduling policies. They | ||
| - | are divided into non real-time and real-time policies. The scheduling | ||
| - | policies are already implemented in mainline Linux. | ||
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| - | **Non real-time policies:** | ||
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| - | * **SCHED_OTHER:** Every task gets a so called 'nice value'. It is a value between -20 for the highest nice value and 19 for the lowest nice value. The average value of execution time of the task depends on the associated nice value. | ||
| - | * **SCHED_BATCH:** This policy is derived from SCHED_OTHER and is optimized for throughput. | ||
| - | * **SCHED_IDLE:** It is also derived from SCHED_OTHER, but it has nice values weaker than 19. | ||
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| - | **Real-time policies:** | ||
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| - | * **SCHED_FIFO:** Tasks have a priority between 1 (low) and 99 (high). A task running under this policy is scheduled until it finishes or a higher prioritized task preempts it. | ||
| - | * **SCHED_RR:** This policy is derived from SCHED_FIFO. The difference to SCHED_FIFO is that a task runs for the duration of a defined time slice (if it is not preempted by a higher prioritized task). It can be interrupted by a task with the same priority once the time slice is used up. The time slice definition is exported in procfs (/proc/sys/kernel/sched_rr_timeslice_ms). | ||
| - | * **SCHED_DEADLINE:** This policy implements the Global Earliest Deadline First (GEDF) algorithm. Tasks scheduled under this policy can preempt any task scheduled with SCHED_FIFO or SCHED_RR. | ||
realtime/documentation/technical_basics/sched_policy_prio.1512462147.txt.gz ยท Last modified: 2017/12/05 08:22 by anna-maria
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