GENWiki

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 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 ker-
            nels).

     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 quan-
     tum 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

     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at
     https://www.kernel.org/doc/man-pages/.

Linux 2017-09-15 SCHED_RR_GET_INTERVAL(2)