sched_setscheduler, sched_getscheduler - set and get scheduling policy/parameters

#include <sched.h>

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

int sched_getscheduler(pid_t pid);

The sched_setscheduler() system call sets both the scheduling policy and parameters for the thread whose ID is specified in pid. If pid equals zero, the scheduling policy and parameters of the calling thread will be set.

The scheduling parameters are specified in the param argument, which is a pointer to a structure of the following form:

struct sched_param {
    ...
    int sched_priority;
    ...
};

In the current implementation, the structure contains only one field, sched_priority. The interpretation of param depends on the selected policy.

Currently, Linux supports the following "normal" (i.e., non-real-time) scheduling policies as values that may be specified in policy:

SCHED_OTHER

the standard round-robin time-sharing policy;

SCHED_BATCH

for "batch" style execution of processes; and

SCHED_IDLE

for running very low priority background jobs.

For each of the above policies, param->sched_priority must be 0.

Various "real-time" policies are also supported, for special time-critical applications that need precise control over the way in which runnable threads are selected for execution. For the rules governing when a process may use these policies, see sched(7). The real-time policies that may be specified in policy are:

SCHED_FIFO

a first-in, first-out policy; and

SCHED_RR

a round-robin policy.

For each of the above policies, param->sched_priority specifies a scheduling priority for the thread. This is a number in the range returned by calling sched_get_priority_min(2) and sched_get_priority_max(2) with the specified policy. On Linux, these system calls return, respectively, 1 and 99.

Since Linux 2.6.32, the SCHED_RESET_ON_FORK flag can be ORed in policy when calling sched_setscheduler(). As a result of including this flag, children created by fork(2) do not inherit privileged scheduling policies. See sched(7) for details.

sched_getscheduler() returns the current scheduling policy of the thread identified by pid. If pid equals zero, the policy of the calling thread will be retrieved.

On success, sched_setscheduler() returns zero. On success, sched_getscheduler() returns the policy for the thread (a nonnegative integer). On error, both calls return -1, and errno is set appropriately.

chrt(1), nice(2), sched_get_priority_max(2), sched_get_priority_min(2), sched_getaffinity(2), sched_getattr(2), sched_getparam(2), sched_rr_get_interval(2), sched_setaffinity(2), sched_setattr(2), sched_setparam(2), sched_yield(2), setpriority(2), capabilities(7), cpuset(7), sched(7)