chill Action

void chill(int nanoseconds)

The chill action causes DTrace to spin for the specified number of nanoseconds. chill is primarily useful for exploring problems that might be timing related. For example, you can use this action to open race condition windows, or to bring periodic events into or out of phase with one another. Because interrupts are disabled while in DTrace probe context, any use of chill can induce interrupt latency, scheduling latency, and dispatch latency. Therefore, chill can cause unexpected systemic effects and it must not be used indiscriminately. Because system activity relies on periodic interrupt handling, DTrace will refuse to execute the chill action for more than 500 milliseconds out of each one-second interval on any given CPU. If the maximum chill interval is exceeded, DTrace will report an illegal operation error, as shown in the following example:

# dtrace -w -n syscall::openat:entry'{chill(500000001)}'
dtrace: allowing destructive actions
dtrace: description 'syscall::openat:entry' matched 1 probe
dtrace: 57 errors
CPU     ID                    FUNCTION:NAME
dtrace: error on enabled probe ID 1 (ID 14: syscall::openat:entry): \
  illegal operation in action #1

This limit is enforced even if the time is spread across multiple calls to chill, or multiple DTrace consumers of a single probe. For example, the same error would be generated by the following command:

# dtrace -w -n syscall::openat:entry'{chill(250000000); chill(250000001);}'