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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, 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 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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