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)

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