PR_SET_TIMERSLACK(2const) — Linux manual page

PR_SET_TIMERSLACK(2const)                      PR_SET_TIMERSLACK(2const)

NAME

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

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <linux/prctl.h>  /* Definition of PR_* constants */
       #include <sys/prctl.h>

       int prctl(PR_SET_TIMERSLACK, unsigned long slack);

DESCRIPTION

       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).

RETURN VALUE

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

FILES

       /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

       Linux.

HISTORY

       Linux 2.6.28.

SEE ALSO

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

COLOPHON

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Linux man-pages 6.9.1          2024-06-02      PR_SET_TIMERSLACK(2const)

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

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