sched_rr_get_interval - get the SCHED_RR interval for the named process
Standard C library (
libc,
-lc)
#include <sched.h>
int sched_rr_get_interval(pid_t pid, struct timespec *tp);
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.
On success,
sched_rr_get_interval() returns 0. On error, -1 is returned,
and
errno is set to indicate the error.
- 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.
POSIX.1-2001, POSIX.1-2008.
POSIX systems on which
sched_rr_get_interval() is available define
_POSIX_PRIORITY_SCHEDULING in
<unistd.h>.
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.
timespec(3),
sched(7)