SCHED(3)

NAME
sched_setparam, sched_getparam, sched_setscheduler, sched_getscheduler, sched_get_priority_max, sched_get_priority_min, sched_rr_get_interval, sched_yield, sched_protect, sched_setaffinity_np, sched_getaffinity_np - process scheduling

LIBRARY
librt

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);
int
sched_setscheduler(pid_t pid, int policy, const struct sched_param *param);
int
sched_getscheduler(pid_t pid);
int
sched_get_priority_max(int policy);
int
sched_get_priority_min(int policy);
int
sched_rr_get_interval(pid_t pid, struct timespec *interval);
int
sched_yield(void);
int
sched_setaffinity_np(pid_t pid, size_t size, cpuset_t *cpuset);
int
sched_getaffinity_np(pid_t pid, size_t size, cpuset_t *cpuset);
int
sched_protect(int priority);

DESCRIPTION
This section describes the functions used to get scheduling information about processes, and control the scheduling of processes.

Available scheduling policies (classes) are:

SCHED_OTHER
    Time-sharing (TS) scheduling policy. The default policy in NetBSD.

SCHED_FIFO
    First in, first out (FIFO) scheduling policy.

SCHED_RR
    Round robin scheduling policy.

The struct sched_param contains at least one member:

sched_priority
    Specifies the priority of the process. For SCHED_OTHER, must be PRI_NONE; the kernel will dynamically assign priorities to the thread based on CPU load.

FUNCTIONS

sched_setparam(pid, param)
    Sets the scheduling parameters for the process specified by pid to param. If the value of pid is equal to zero, then the calling process is used.

sched_getparam(pid, param)
    Gets the scheduling parameters of the process specified by pid into the structure param. If the value of pid is equal to zero, then the calling process is used.

sched_setscheduler(pid, policy, param)
    Set the scheduling policy and parameters for the process specified by pid. If the value of pid is equal to zero, then the calling process is used.

sched_getscheduler(pid)
    Returns the scheduling policy of the process specified by pid. If the value of pid is equal to zero, then the calling process is used.

sched_get_priority_max(policy)
    Returns the maximal priority which may be used for the scheduling policy specified by policy.

sched_get_priority_min(policy)
    Returns the minimal priority which may be used for the scheduling policy specified by policy.

sched_rr_get_interval(pid, interval)
    Returns the time quantum into the structure interval of the process specified by pid. If the value of pid is equal to zero, then the calling process is used. The process must be running at SCHED_RR scheduling policy.

sched_yield()
    Yields a processor voluntarily and gives other threads a chance to run without waiting for an involuntary preemptive switch.

sched_setaffinity_np(pid, size, cpuset)
    Set the affinity mask specified by cpuset for the process specified by pid. At least one valid CPU must be set in the mask.

sched_getaffinity_np(pid, size, cpuset)
    Get the affinity mask of the process specified by pid into the cpuset.

sched_protect(priority)
    Performs priority protection using the PTHREAD_PRIO_PROTECT protocol. This function will increase the protected priority of the caller thread to priority if the current thread's protected priority is smaller than priority. Multiple calls to sched_protect() with a positive priority will “push” a priority level to the current thread, whereas calling sched_protect() with a priority level of -1 will “pop” a priority level. When the level reaches 0 (the same number of “pushes” and “pops” have been issued) the original thread priority will be restored.

IMPLEMENTATION NOTES
Setting CPU affinity(3) requires super-user privileges. Ordinary users can be allowed to control CPU affinity of their threads via the security.models.extensions.user_set_cpu_affinity sysctl(7). See secmodel_extensions(9).

Portable applications should not use the sched_setaffinity_np() and sched_getaffinity_np() functions.

RETURN VALUES
sched_protect(), sched_setparam(), sched_getparam(), sched_rr_get_interval(), and sched_yield() return 0 on success. Otherwise, -1 is returned and errno is set to indicate the error.

sched_setscheduler() returns the previously used scheduling policy on success. Otherwise, -1 is returned and errno is set to indicate the error.

sched_getscheduler() returns the scheduling policy on success. Otherwise, -1 is returned and errno is set to indicate the error.

sched_get_priority_max() and sched_get_priority_min() return the maximal/minimal priority value on success. Otherwise, -1 is returned and errno is set to indicate the error.

sched_setaffinity_np() and sched_getaffinity_np() return 0 on success. Otherwise, -1 is returned and errno is set to indicate the error.

ERRORS
The sched_setparam() and sched_setscheduler() functions fail if:

[EINVAL]
    At least one of the specified scheduling parameters was invalid.

[EPERM]
    The calling process has no appropriate privileges to perform the operation.

[ESRCH]
    No process can be found corresponding to the PID specified by pid, and the value of pid is not zero.

The sched_getparam() and sched_getscheduler() functions fail if:

[EPERM]
    The calling process is not a super-user and its effective user id does not match the effective user-id of the specified process.

[ESRCH]
    No process can be found corresponding to that specified by pid, and the value of pid is not zero.

The sched_get_priority_max() and sched_get_priority_min() functions fail if:

[EINVAL]
    The specified scheduling policy is invalid.

The sched_rr_get_interval() function fails if:

[ESRCH]
    No process can be found corresponding to that specified by pid, and the value of pid is not zero.

The sched_protect() function fails if:

[EINVAL]
    The thread was not priority protected.

[EPERM]
    The priority parameter was out of range (not in the range between SCHED_PRIO_MIN and SCHED_PRIO_MAX).

SEE ALSO
affinity(3), cpuset(3), pset(3), schedctl(8)

STANDARDS
These functions, except sched_setaffinity_np() and sched_getaffinity_np(), are expected to conform the p1003.1-2001 standard.

HISTORY
The scheduling functions appeared in NetBSD 5.0.