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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