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# Timer Slack
[Timer objects](/docs/reference/kernel_objects/ have a concept of slack. Slack
defines how the system may alter the timer's deadline. Slack allows
the system to internally coalesce timers and timer-like events to
improve performance or efficiency.
Slack is made up of two components, type and amount. Type describes
how slack can be applied:
+ **ZX_TIMER_SLACK_CENTER** coalescing is allowed with earlier and
later timers.
+ **ZX_TIMER_SLACK_EARLY** coalescing is allowed only with earlier
+ **ZX_TIMER_SLACK_LATE** coalescing is allowed only with later
Amount is the allowed deviation from the deadline. For example, a
timer with **ZX_TIMER_SLACK_EARLY** and 5us may fire up to 5us before
its deadline. A timer with **ZX_TIMER_SLACK_CENTER** and 7ms may fire
anywhere from 7ms before its deadline to 7ms after its deadline.
## Timer-like Syscalls
Slack may also be applied to blocking syscalls that accept a deadline
argument, like [`zx_nanosleep()`].
## Defaults and Job Policy
For Timer objects, slack is specified when creating and setting
timers. For other syscalls that take a deadline, but no slack
parameters, the slack type and amount are specified by the job's
policy. See [`zx_job_set_policy()`].
[`zx_job_set_policy()`]: /docs/reference/syscalls/
[`zx_nanosleep()`]: /docs/reference/syscalls/