SCHED_RR_GET_INTERVAL
Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
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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 kernels).
- 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 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.
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 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- Linux notes
-
- SEE ALSO
-
- COLOPHON
-
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