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Name

sched_rr_get_interval - get the SCHED_RR interval for the named process

Synopsis

#include <sched.h>

int sched_rr_get_interval(pid_t pid, struct timespec * tp);

Description

sched_rr_get_interval() writes into the timespec structure pointed to by tp the round-robin time quantum for the process identified by pid. The specified process should be running under the SCHED_RR scheduling policy.

The timespec structure has the following form: 


struct timespec {
    time_t tv_sec;    /* seconds */
    long   tv_nsec;   /* nanoseconds */
};

If pid is zero, the time quantum for the calling process is written into *tp.

Return Value

On success, sched_rr_get_interval() returns 0. On error, -1 is returned, and errno is set appropriately.

Errors

EFAULT
Problem with copying information to user space.
EINVAL
Invalid pid.
ENOSYS
The system call is not yet implemented (only on rather old kernels).
ESRCH
Could not find a process with the ID pid.

Conforming to

POSIX.1-2001.

Notes

POSIX systems on which sched_rr_get_interval() is available define _POSIX_PRIORITY_SCHEDULING in <unistd.h>.

Linux notes

POSIX does not specify any mechanism for controlling the size of the round-robin time quantum. Older Linux kernels provide a (nonportable) method of doing this. The quantum can be controlled by adjusting the process’s nice value (see setpriority(2) ). Assigning a negative (i.e., high) nice value results in a longer quantum; assigning a positive (i.e., low) nice value results in a shorter quantum. The default quantum is 0.1 seconds; the degree to which changing the nice value affects the quantum has varied somewhat across kernel versions. This method of adjusting the quantum was removed starting with Linux 2.6.24.

Linux 3.9 added a new mechanism for adjusting (and viewing) the SCHED_RR quantum: the /proc/sys/kernel/sched_rr_timeslice_ms file exposes the quantum as a millisecond value, whose default is 100. Writing 0 to this file resets the quantum to the default value.

See Also

sched(7)

Colophon

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