How do I use different timers when profiling an application?

The timestamps of method entry/exit events can be taken using different kinds of OS timers. By default, absolute timer is used to measure absolute, or wall clock time. Thread CPU timer measures only the time spent executing the given thread. Essentially, the OS suspends this timer every time the CPU stops executing the code on behalf of the given thread, and resumes it every time execution switches back to this thread.

About using different kinds of timers

By default, the results only display the elapsed, or absolute, time spent in profiled methods. Note, though, that the IDE always attempts to give you both the absolute and thread CPU time for your whole profiled call subgraph. This time is measured as an interval between the time the given thread entered the root method and the time that it exited this method, minus the estimated time spent in the injected instrumentation code. Absolute time for the whole subgraph is always shown. Thread CPU time, however, is shown only if thread CPU time measuring at method level is active (see below), or if at the moment when you request the data, the given execution thread is not within the call subgraph. Otherwise, the Profiler says that thread CPU time is unavailable. This is a purely technical limitation, which may be eliminated in future.

If you profile a multi-threaded application, it often makes sense to measure thread CPU time for profiled methods in addition to, or instead of, the absolute time. You can choose between measuring only absolute, only thread CPU, or both times. Note that if you turn on both timers, the profiling overhead will increase, since the instrumentation that we inject into the target application code will have to make two timer calls instead of one every time an application method is entered or exited. Note also that on Windows and Linux, the resolution of the thread CPU timer is very low - about 10 ms, compared to a fraction of a microsecond for the absolute timer. Thus it makes little sense to use the thread CPU timer for individual methods on these platforms, at least if these methods tend to run for less than, say, 50..100 ms. On Solaris, the situation is considerably better - the resolution of the thread CPU timer on this OS is about 1 ms, and the call to this timer also takes much fewer CPU cycles than on Windows (on the order of 10 times fewer).

Applies to: NetBeans 5.5/6.*/7.*

Platforms: All

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