NAME

sched_setscheduler, sched_getscheduler —

set/get scheduling policy and scheduler parameters

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sched.h>

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

int
sched_getscheduler(pid_t pid);

DESCRIPTION

The sched_setscheduler() system call sets the scheduling policy and scheduling parameters of the process specified by pid to policy and the parameters specified in the sched_param structure pointed to by param, respectively. The value of the sched_priority member in the param structure must be any integer within the inclusive priority range for the scheduling policy specified by policy.

In this implementation, if the value of pid is negative the system call will fail.

If a process specified by pid exists and if the calling process has permission, the scheduling policy and scheduling parameters will be set for the process whose process ID is equal to pid.

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

In this implementation, the policy of when a process can affect the scheduling parameters of another process is specified in IEEE Std 1003.1b-1993 (“POSIX.1b”) as a write-style operation.

The scheduling policies are in <sched.h>:

[SCHED_FIFO]: First-in-first-out fixed priority scheduling with no round robin scheduling;
[SCHED_OTHER]: The standard time sharing scheduler;
[SCHED_RR]: Round-robin scheduling across same priority processes.

The sched_param structure is defined in <sched.h>:

struct sched_param {
	int sched_priority;	/* scheduling priority */
};

The sched_getscheduler() system call returns the scheduling policy of the process specified by pid.

If a process specified by pid exists and if the calling process has permission, the scheduling parameters for the process whose process ID is equal to pid are returned.

In this implementation, the policy of when a process can obtain the scheduling parameters of another process are detailed in IEEE Std 1003.1b-1993 (“POSIX.1b”) as a read-style operation.

If pid is zero, the scheduling parameters for the calling process will be returned. In this implementation, the sched_getscheduler system call will fail if pid is negative.

RETURN VALUES

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

ERRORS

On failure errno will be set to the corresponding value:

[ENOSYS]: The system is not configured to support this functionality.
[EPERM]: The requesting process doesn not have permission as detailed in IEEE Std 1003.1b-1993 (“POSIX.1b”).
[ESRCH]: No process can be found corresponding to that specified by pid.
[EINVAL]: The value of the policy argument is invalid, or one or more of the parameters contained in param is outside the valid range for the specified scheduling policy.

STANDARDS

The sched_setscheduler() and sched_getscheduler() system calls conform to IEEE Std 1003.1b-1993 (“POSIX.1b”).