.. _nanos6-stats-instrumentation:

Obtaining statistics
--------------------

.. index::
    triple: Nanos6; stats; instrumentation

To enable collecting statistics, run the application with the ``version.instrument`` configuration variable set to ``stats``.
This variant collects timing statistics.

By default, the statistics are emitted to the standard error when the program ends.
The output can be sent to a file through the ``instrument.stats.output_file`` configuration option.

The contents of the output contains the average for each task type and the total task average of the following metrics:

* Number of instances
* Mean instantiation time
* Mean pending time (not ready due to dependencies)
* Mean ready time
* Mean execution time
* Mean blocked time (due to a critical or a taskwait)
* Mean zombie time (finished but not yet destroyed)
* Mean lifetime (time between creation and destruction)

The output also contains information about:

* Number of CPUs
* Total number of threads
* Mean threads per CPU
* Mean tasks per thread
* Mean thread lifetime
* Mean thread running time

Most codes consist of an initialization phase, a calculation phase and final phase for verification or writing the results.
Usually these phases are separated by a taskwait.
The runtime uses the taskwaits at the outermost level to identify phases and emit individual metrics for each phase.