Timer 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 timers.
- ZX_TIMER_SLACK_LATE coalescing is allowed only with later timers.
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().