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Timer Slack

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().