sched_rr_get_interval(2) - Linux manual page (original) (raw)

schedrrgetinterval(2) System Calls Manual schedrrgetinterval(2)

NAME top

   sched_rr_get_interval - get the SCHED_RR interval for the named
   process

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <sched.h>**

   **int sched_rr_get_interval(pid_t** _pid_**, struct timespec ***_tp_**);**

DESCRIPTION top

   **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 top

   On success, **sched_rr_get_interval**() returns 0.  On error, -1 is
   returned, and _[errno](../man3/errno.3.html)_ is set to indicate the error.

ERRORS top

   **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 top

Linux Linux 3.9 added a new mechanism for adjusting (and viewing) the SCHED_RR quantum: the /proc/sys/kernel/schedrrtimeslicems 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 top

   POSIX.1-2008.

HISTORY top

   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 top

   POSIX systems on which **sched_rr_get_interval**() is available define
   **_POSIX_PRIORITY_SCHEDULING** in _<unistd.h>_.

COLOPHON top

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Linux man-pages 6.10 2024-07-23 schedrrgetinterval(2)

Pages that refer to this page:sched_setattr(2), sched_setscheduler(2), syscalls(2), proc_sys_kernel(5), sched(7)