sched_rr_get_interval(2) System Calls Manual sched_rr_get_interval(2)
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 sched-
uling 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 re-
turned, 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 ker-
nels).
ESRCH Could not find a process with the ID pid.
STANDARDS
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 ex-
poses the quantum as a millisecond value, whose default is 100. Writ-
ing 0 to this file resets the quantum to the default value.
SEE ALSO
timespec(3), sched(7)
Linux man-pages 6.03 2022-10-30 sched_rr_get_interval(2)
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