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sched_rr_get_interval(2) System Calls Manual sched_rr_get_interval(2)


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.


Problem with copying information to user space.
Invalid pid.
The system call is not yet implemented (only on rather old kernels).
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>.

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.


timespec(3), sched(7)

2022-10-30 Linux man-pages 6.03