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linuxlinux-kernelschedulingscheduler
Nadav Peled
Nadav Peled

Reputation: 1011

What does sched_priority in struct sched_param refer to?

im having some hard time understanding the sched_priority role in the setscheduler func.
Im using linux 2.4.X, and the documentation says : 

Valid priorities for SCHED_OTHER is 0, Valid priorities for SCHED_RR\FIFO are 1...MAX_USER_RT_PRIO-1

But, I remember that priorities for rt procsses are 0-99, and for SCHED_OTHER 100-139, so... what did I miss ? what sched_priority in struct sched_param refers to?

Upvotes: 1

Views: 3981

Answers (2)

gby
gby

Reputation: 15218

You are confusing the user space interface with the internal kernel implementation. sched_priority is just the requested fixed real time priority. A task scheduled under the SCHED_OTHER policy also has a nice level.

The scale you remember is the kernel internal representation of the relative priority of a task, aggregating real time tasks and SCHED_OTHER tasks with their respective nice levels.

Upvotes: 0

Karthik Balaguru
Karthik Balaguru

Reputation: 7842

SCHED_OTHER is the default scheduling policy with round robin. This is has no choice of priority.

SCHED_FIFO and SCHED_RR are real time scheduling policies for which the priority range from 1 to 99.

SCHED_OTHER, SCHED_BATCH and SCHED_IDLE are normal scheduling policies.

From Linux 3.14 onwards, you will find SCHED_DEADLINE that in which the task with earliest deadline is executed first.

You can use the sched_priority to set the thread priority. sched_priority is a member of the structure struct sched_param.

Try out chrt -m to check the min/max valid priorities that can be configured/set. chrt can be used to set or retrieve scheduling attributes of processes.

Upvotes: 2

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