Profile Provider

The profile provider includes probes that are associated with an interrupt that fires at some regular, specified time interval.

Such probes aren't associated with any particular point of execution, but rather with the asynchronous interrupt event. You can use these probes to sample some aspect of the system state and then use the samples to infer system behavior. If the sampling rate is high or the sampling time is long, an accurate inference is possible. Using DTrace functions, you can use the profile provider to sample many aspects of the system. For example, you could sample the state of the current thread, the state of the CPU, or the current machine instruction.

profile-n Probes

The profile-n probes fire at a fixed interval, at a high-interrupt level on all active CPUs.

The units of n default to a frequency that's expressed as a rate of firing per second, but the value can also have an optional suffix , as shown in Table 8-1, which specifies either a time interval or a frequency. The following table describes valid time suffixes for a tick- n probe.

Table 8-1 Valid Time Suffixes

Suffix	Time Units
nsec or ns	nanoseconds
usec or us	microseconds
msec or ms	milliseconds
sec or s	seconds
min or m	minutes
hour or h	hours
day or d	days
hz	hertz (frequency expressed as rate per second)

tick-n Probes

The tick-n probes fire at fixed intervals, at a high interrupt level on only one CPU per interval.

Unlike profile-n probes, which fire on every CPU, tick-n probes fire on only one CPU per interval and the CPU on which they fire can change over time. The units of n default to a frequency expressed as a rate of firing per second, but the value can also have an optional time suffix as shown in Table 8-1, which specifies either a time interval or a frequency.

The tick-n probes have several uses, such as providing some periodic output or taking a periodic action.

Note:

The highest available tick frequency is 5000 Hz (tick-5000).

profile Probe Arguments

The following table describes the arguments for the profile probes.

Table 8-2 profile Probe Arguments

Probe	arg0	arg1
profile-n	pc	upc
tick-n	pc	upc

The arguments are as follows:

• pc: kernel program counter

• upc: user-space program counter

profile Probe Creation

Unlike other providers, the profile provider creates probes dynamically on an as-needed basis. Thus, the preferred probe might not appear in a listing of all probes, for example, when using the dtrace -l -P profile command, but the probe is created when it's explicitly enabled.

A time interval that's too short causes the machine to continuously field time-based interrupts and denies service on the machine. The profile provider refuses to create a probe that would result in an interval of less than two hundred microseconds and returns an error.

prof Stability

The profile provider uses DTrace's stability mechanism to describe its stabilities. These stability values are listed in the following table.

Element	Name Stability	Data Stability	Dependency Class
Provider	Evolving	Evolving	Common
Module	Unstable	Unstable	Unknown
Function	Private	Private	Unknown
Name	Evolving	Evolving	Common
Arguments	Evolving	Evolving	Common