sched_setscheduler(S)

sched_setscheduler -- set scheduling policy

Syntax

cc . . . -lc

#include <sched.h>

int sched_setscheduler(pid_t pid, int policy, const struct sched_param
*param);

Description

sched_setscheduler sets the scheduling policy of the process specified by pid to policy and the scheduling parameters to param.

If pid is 0, the policy and parameters are set for the calling process.

The following policies are available:

SCHED_FIFO: first in first out. Processes are allowed on the CPU in the order in which they were added to the queue of processes to be run, for each priority.
SCHED_RR: round-robin. Identical to SCHED_FIFO except that a process runs only for a set time slice (see sched_rr_get_interval(S)). Once the process has completed its time slice it is placed on the tail of the queue of processes to be run, for its priority.
SCHED_OTHER: non-realtime scheduling. This uses the traditional UNIX scheduler.

On MPX systems, if pid specifies a process currently running on a different CPU then the process specified by pid will be taken off the CPU. This is the equivalent of the process specified by pid making a call to sched_yield. The process which made the call to sched_setscheduler will sleep while this occurs.

Return values

Upon successful completion sched_setscheduler returns the previous scheduling policy of the process specified by pid. If an error has occurred the policy and scheduling parameters of the target process will remain unchanged, sched_setparam returns -1, and errno is set to indicate the error.

Diagnostics

If sched_setscheduler terminates due to an error, it will set errno to one of the following values:

[EINVAL]: One or more of the scheduling parameters specified is out of the range defined for the specified process's scheduling policy, or the specified policy is incorrect.
[ENOSYS]: The function is not supported.
[EPERM]: The requesting process does not have permission to set either or both of the scheduling parameters, or the scheduling policy of the process specified by pid.
[ESRCH]: The process, specified by pid, does not exist.

Examples

The following example illustrates the use of sched_setscheduler:

   struct sched_param sp;
   int policy;
   ...
   if((policy = sched_getscheduler(0) == -1)) {
      fprintf(stderr, ...
   }
   
   if(policy == SCHED_OTHER) {
      sp.sched_priority = sched_get_priority_max(SCHED_FIFO);
      sched_setscheduler(0, SCHED_FIFO, &sp)
      ...
   }
   ...

Files

/usr/lib/libc.a: linking library

Standards conformance

Text reprinted and/or adapted from IEEE Std 1003.1b-1993, IEEE Standard for Information Technology, POSIX Part 1: System Application Program Interface (API) Amendment 1: Realtime Extensions [C Language], copyright © 1993 by the Institute of Electrical and Electronics Engineers, Inc. The IEEE takes no responsibility for and will assume no liability for damages resulting from the reader's misinterpretation of said information resulting from the placement and context in this publication. Information is reproduced with the permission of the IEEE.