sched_rr_get_interval(2)

1sched_rr_get_interval(2)      System Calls Manual     sched_rr_get_interval(2)
2
3
4

NAME

6       sched_rr_get_interval - get the SCHED_RR interval for the named process
7

LIBRARY

9       Standard C library (libc, -lc)
10

SYNOPSIS

12       #include <sched.h>
13
14       int sched_rr_get_interval(pid_t pid, struct timespec *tp);
15

DESCRIPTION

17       sched_rr_get_interval()  writes  into the timespec(3) structure pointed
18       to by tp the round-robin time quantum for  the  process  identified  by
19       pid.  The specified process should be running under the SCHED_RR sched‐
20       uling policy.
21
22       If pid is zero, the time quantum for the  calling  process  is  written
23       into *tp.
24

RETURN VALUE

26       On  success,  sched_rr_get_interval()  returns  0.  On error, -1 is re‐
27       turned, and errno is set to indicate the error.
28

ERRORS

30       EFAULT Problem with copying information to user space.
31
32       EINVAL Invalid pid.
33
34       ENOSYS The system call is not yet implemented (only on rather old  ker‐
35              nels).
36
37       ESRCH  Could not find a process with the ID pid.
38

VERSIONS

40   Linux
41       Linux  3.9  added  a  new  mechanism  for  adjusting  (and viewing) the
42       SCHED_RR quantum: the /proc/sys/kernel/sched_rr_timeslice_ms  file  ex‐
43       poses  the quantum as a millisecond value, whose default is 100.  Writ‐
44       ing 0 to this file resets the quantum to the default value.
45

STANDARDS

47       POSIX.1-2008.
48

HISTORY

50       POSIX.1-2001.
51
52   Linux
53       POSIX does not specify any mechanism for controlling the  size  of  the
54       round-robin  time quantum.  Older Linux kernels provide a (nonportable)
55       method of doing this.  The quantum can be controlled by  adjusting  the
56       process's nice value (see setpriority(2)).  Assigning a negative (i.e.,
57       high) nice value results in a  longer  quantum;  assigning  a  positive
58       (i.e., low) nice value results in a shorter quantum.  The default quan‐
59       tum is 0.1 seconds; the degree to which changing the nice value affects
60       the quantum has varied somewhat across kernel versions.  This method of
61       adjusting the quantum was removed starting with Linux 2.6.24.
62

NOTES

64       POSIX systems on  which  sched_rr_get_interval()  is  available  define
65       _POSIX_PRIORITY_SCHEDULING in <unistd.h>.
66