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SCHED_RR_GET_INTERVAL(2)                                                Linux Programmer's Manual                                               SCHED_RR_GET_INTERVAL(2)

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 to indicate the error.

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, POSIX.1-2008.

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 quan‐
       tum; 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 mil‐
       lisecond value, whose default is 100.  Writing 0 to this file resets the quantum to the default value.

SEE ALSO
       sched(7)

Linux                                                                          2021-03-22                                                       SCHED_RR_GET_INTERVAL(2)