sched_rr_get_interval(2)

1SCHED_RR_GET_INTERVAL(2)   Linux Programmer's Manual  SCHED_RR_GET_INTERVAL(2)
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NAME

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

9       #include <sched.h>
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11       int sched_rr_get_interval(pid_t pid, struct timespec *tp);
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DESCRIPTION

14       sched_rr_get_interval()  writes  into the timespec structure pointed to
15       by tp the round-robin time quantum for the process identified  by  pid.
16       The  specified  process should be running under the SCHED_RR scheduling
17       policy.
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19       The timespec structure has the following form:
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21           struct timespec {
22               time_t tv_sec;    /* seconds */
23               long   tv_nsec;   /* nanoseconds */
24           };
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26       If pid is zero, the time quantum for the  calling  process  is  written
27       into *tp.
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RETURN VALUE

30       On  success,  sched_rr_get_interval()  returns  0.  On error, -1 is re‐
31       turned, and errno is set to indicate the error.
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ERRORS

34       EFAULT Problem with copying information to user space.
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36       EINVAL Invalid pid.
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38       ENOSYS The system call is not yet implemented (only on rather old  ker‐
39              nels).
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41       ESRCH  Could not find a process with the ID pid.
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CONFORMING TO

44       POSIX.1-2001, POSIX.1-2008.
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NOTES

47       POSIX  systems  on  which  sched_rr_get_interval()  is available define
48       _POSIX_PRIORITY_SCHEDULING in <unistd.h>.
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50   Linux notes
51       POSIX does not specify any mechanism for controlling the  size  of  the
52       round-robin  time quantum.  Older Linux kernels provide a (nonportable)
53       method of doing this.  The quantum can be controlled by  adjusting  the
54       process's nice value (see setpriority(2)).  Assigning a negative (i.e.,
55       high) nice value results in a  longer  quantum;  assigning  a  positive
56       (i.e., low) nice value results in a shorter quantum.  The default quan‐
57       tum is 0.1 seconds; the degree to which changing the nice value affects
58       the quantum has varied somewhat across kernel versions.  This method of
59       adjusting the quantum was removed starting with Linux 2.6.24.
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61       Linux 3.9 added  a  new  mechanism  for  adjusting  (and  viewing)  the
62       SCHED_RR  quantum:  the /proc/sys/kernel/sched_rr_timeslice_ms file ex‐
63       poses the quantum as a millisecond value, whose default is 100.   Writ‐
64       ing 0 to this file resets the quantum to the default value.
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COLOPHON

70       This  page  is  part of release 5.13 of the Linux man-pages project.  A
71       description of the project, information about reporting bugs,  and  the
72       latest     version     of     this    page,    can    be    found    at
73       https://www.kernel.org/doc/man-pages/.
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77Linux                             2021-03-22          SCHED_RR_GET_INTERVAL(2)