NAME

sched_setparam, sched_getparam —

set/get scheduling parameters

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sched.h>

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

int
sched_getparam(pid_t pid, struct sched_param *param);

DESCRIPTION

The sched_setparam() system call sets the scheduling parameters of the process specified by pid to the values specified by the sched_param structure pointed to by param. The value of the sched_priority member in the param structure must be any integer within the inclusive priority range for the current scheduling policy of the process specified by pid. Higher numerical values for the priority represent higher priorities.

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 parameters are set for the process whose process ID is equal to pid.

If pid is zero, the 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 target process, whether it is running or not running, will resume execution after all other runnable processes of equal or greater priority have been scheduled to run.

If the priority of the process specified by the pid argument is set higher than that of the lowest priority running process and if the specified process is ready to run, the process specified by the pid argument will preempt a lowest priority running process. Similarly, if the process calling sched_setparam() sets its own priority lower than that of one or more other nonempty process lists, then the process that is the head of the highest priority list will also preempt the calling process. Thus, in either case, the originating process might not receive notification of the completion of the requested priority change until the higher priority process has executed.

In this implementation, when the current scheduling policy for the process specified by pid is normal timesharing (SCHED_OTHER, aka SCHED_NORMAL when not POSIX-source) or the idle policy (SCHED_IDLE when not POSIX-source) then the behavior is as if the process had been running under SCHED_RR with a priority lower than any actual realtime priority.

The sched_getparam() system call will return the scheduling parameters of a process specified by pid in the sched_param structure pointed to by param.

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_getparam 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]: For sched_setparam(): one or more of the requested scheduling parameters is outside the range defined for the scheduling policy of the specified pid.

STANDARDS

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