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PR_SET_TIMERSLACK(2const) — Linux manual page

PR_SET_TIMERSLACK(2const)PR_SET_TIMERSLACK(2const)

NAME        top

       PR_SET_TIMERSLACK - set the "current" timer slack value for the       calling thread

LIBRARY        top

       Standard C library (libc,-lc)

SYNOPSIS        top

#include <linux/prctl.h>/* Definition ofPR_*constants */#include <sys/prctl.h>int prctl(PR_SET_TIMERSLACK, unsigned longslack);

DESCRIPTION        top

       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 inslack is greater than zero, then the "current" value       is set to this value.  Ifslack is0L, 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 byselect(2),pselect(2),poll(2),ppoll(2),epoll_wait(2),epoll_pwait(2),clock_nanosleep(2),nanosleep(2), andfutex(2)       (and thus the library functions implemented via futexes, includingpthread_cond_timedwait(3),pthread_mutex_timedlock(3),pthread_rwlock_timedrdlock(3),pthread_rwlock_timedwrlock(3), andsem_timedwait(3)).       Timer slack is not applied to threads that are scheduled under a       real-time scheduling policy (seesched_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       viaPR_SET_TIMERSLACK.  The "default" value can't be changed.  The       timer slack values ofinit (PID 1), the ancestor of all processes,       are 50,000 nanoseconds (50 microseconds).  The timer slack value       is inherited by a child created viafork(2), and is preserved       acrossexecve(2).

RETURN VALUE        top

       On success, 0 is returned.  On error, -1 is returned, anderrno is       set to indicate the error.

FILES        top

/proc/pid/timerslack_ns              Since Linux 4.6, the "current" timer slack value of any              process can be examined and changed via this file.

STANDARDS        top

       Linux.

HISTORY        top

       Linux 2.6.28.

SEE ALSO        top

prctl(2),PR_GET_TIMERSLACK(2const),proc_pid_timerslack_ns(5)

COLOPHON        top

       This page is part of theman-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 isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17PR_SET_TIMERSLACK(2const)

Pages that refer to this page:prctl(2), PR_GET_TIMERSLACK(2const)

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