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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | FILES | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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PR_SET_TIMERSLACK(2const) PR_SET_TIMERSLACK(2const)
PR_SET_TIMERSLACK - set the "current" timer slack value for the
calling thread
Standard C library (libc, -lc)
#include <linux/prctl.h> /* Definition of PR_* constants */
#include <sys/prctl.h>
int prctl(PR_SET_TIMERSLACK, unsigned long slack);
Each thread has two associated timer slack values: a "default"
value, and a "current" value. This operation sets the "current"
timer slack value for the calling thread. slack is an unsigned
long value in the range [1L, ULONG_MAX]. If the nanosecond value
supplied in slack is greater than zero, then the "current" value
is set to this value. If slack is 0L, the "current" timer slack
is reset to the thread's "default" timer slack value.
The "current" timer slack is used by the kernel to group timer
expirations for the calling thread that are close to one another;
as a consequence, timer expirations for the thread may be up to
the specified number of nanoseconds late (but will never expire
early). Grouping timer expirations can help reduce system power
consumption by minimizing CPU wake-ups.
The timer expirations affected by timer slack are those set by
select(2), pselect(2), poll(2), ppoll(2), epoll_wait(2),
epoll_pwait(2), clock_nanosleep(2), nanosleep(2), and futex(2)
(and thus the library functions implemented via futexes, including
pthread_cond_timedwait(3), pthread_mutex_timedlock(3),
pthread_rwlock_timedrdlock(3), pthread_rwlock_timedwrlock(3), and
sem_timedwait(3)).
Timer slack is not applied to threads that are scheduled under a
real-time scheduling policy (see sched_setscheduler(2)).
When a new thread is created, the two timer slack values are made
the same as the "current" value of the creating thread.
Thereafter, a thread can adjust its "current" timer slack value
via PR_SET_TIMERSLACK. The "default" value can't be changed. The
timer slack values of init (PID 1), the ancestor of all processes,
are 50,000 nanoseconds (50 microseconds). The timer slack value
is inherited by a child created via fork(2), and is preserved
across execve(2).
On success, 0 is returned. On error, -1 is returned, and errno is
set to indicate the error.
/proc/pid/timerslack_ns
Since Linux 4.6, the "current" timer slack value of any
process can be examined and changed via this file.
Linux.
Linux 2.6.28.
prctl(2), PR_GET_TIMERSLACK(2const), proc_pid_timerslack_ns(5)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 PR_SET_TIMERSLACK(2const)
Pages that refer to this page: prctl(2), PR_GET_TIMERSLACK(2const)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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