NAME

       sched_rr_get_interval - get the SCHED_RR interval for the named process

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <sched.h>

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

DESCRIPTION

       sched_rr_get_interval()  writes into the timespec(3) 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.

       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.

VERSIONS

   Linux
       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.

STANDARDS

       POSIX.1-2008.

HISTORY

       POSIX.1-2001.

   Linux
       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.

NOTES

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

SEE ALSO

       timespec(3), sched(7)