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Name

sched_get_priority_max, sched_get_priority_min - get static priority range

Synopsis

#include <sched.h>

int sched_get_priority_max(int policy);

int sched_get_priority_min(int policy);

Description

sched_get_priority_max() returns the maximum priority value that can be used with the scheduling algorithm identified by policy. sched_get_priority_min() returns the minimum priority value that can be used with the scheduling algorithm identified by policy. Supported policy values are SCHED_FIFO, SCHED_RR, SCHED_OTHER, SCHED_BATCH, SCHED_IDLE, and SCHED_DEADLINE. Further details about these policies can be found in sched(7) .

Processes with numerically higher priority values are scheduled before processes with numerically lower priority values. Thus, the value returned by sched_get_priority_max() will be greater than the value returned by sched_get_priority_min().

Linux allows the static priority range 1 to 99 for the SCHED_FIFO and SCHED_RR policies, and the priority 0 for the remaining policies. Scheduling priority ranges for the various policies are not alterable.

The range of scheduling priorities may vary on other POSIX systems, thus it is a good idea for portable applications to use a virtual priority range and map it to the interval given by sched_get_priority_max() and sched_get_priority_min(). POSIX.1-2001 requires a spread of at least 32 between the maximum and the minimum values for SCHED_FIFO and SCHED_RR.

POSIX systems on which sched_get_priority_max() and sched_get_priority_min() are available define _POSIX_PRIORITY_SCHEDULING in <unistd.h>.

Return Value

On success, sched_get_priority_max() and sched_get_priority_min() return the maximum/minimum priority value for the named scheduling policy. On error, -1 is returned, and errno is set appropriately.

Errors

EINVAL
The argument policy does not identify a defined scheduling policy.

Conforming to

POSIX.1-2001.

See Also

sched_getaffinity(2) , sched_getparam(2) , sched_getscheduler(2) , sched_setaffinity(2) , sched_setparam(2) , sched_setscheduler(2) , sched(7)

Colophon

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