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You are here: manpages

SCHED_RR_GET_INTERVAL

Section: Linux Programmer's Manual (2)
Updated: 2007-04-06
Index Return to Main Contents

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 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. The identified process should be running under the SCHED_RR scheduling policy. POSIX systems on which sched_rr_get_interval() is available define _POSIX_PRIORITY_SCHEDULING in <unistd.h>.

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 userspace.
EINVAL: Invalid pid.
ENOSYS: The system call is not yet implemented (only on rather old kernels).
ESRCH: The process whose ID is pid could not be found.

CONFORMING TO

POSIX.1-2001.

NOTES

Linux Notes

POSIX does not specify any mechanism for controlling the size of the round-robin time quantum. However, Linux provides 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.

COLOPHON

This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.