plucky (2) sched_rr_get_interval.2.gz

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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)