derived_measurements.rst - Android社区 - https://www.androidos.net.cn/

Derived Measurements
=====================

The ``DerivedMeasurements`` API provides a consistent way of performing post
processing on a provided :class:`MeasurementCsv` file.

Example
-------

The following example shows how to use an implementation of a
:class:`DerivedMeasurement` to obtain a list of calculated ``DerivedMetric``'s.

.. code-block:: ipython

# Import the relevant derived measurement module
# in this example the derived energy module is used.
In [1]: from devlib import DerivedEnergyMeasurements

# Obtain a MeasurementCsv file from an instrument or create from
# existing .csv file. In this example an existing csv file is used which was
# created with a sampling rate of 100Hz
In [2]: from devlib import MeasurementsCsv
In [3]: measurement_csv = MeasurementsCsv('/example/measurements.csv', sample_rate_hz=100)

# Process the file and obtain a list of the derived measurements
In [4]: derived_measurements = DerivedEnergyMeasurements.process(measurement_csv)

In [5]: derived_measurements
Out[5]: [device_energy: 239.1854075 joules, device_power: 5.5494089227 watts]

API
---

Derived Measurements
~~~~~~~~~~~~~~~~~~~~

.. class:: DerivedMeasurements

The ``DerivedMeasurements`` class provides an API for post-processing
instrument output offline (i.e. without a connection to the target device) to
generate additional metrics.

.. method:: DerivedMeasurements.process(measurement_csv)

Process a :class:`MeasurementsCsv`, returning a list of
:class:`DerivedMetric` and/or :class:`MeasurementsCsv` objects that have been
derived from the input. The exact nature and ordering of the list memebers
is specific to indivial 'class'`DerivedMeasurements` implementations.

.. method:: DerivedMeasurements.process_raw(\*args)

Process raw output from an instrument, returnin a list :class:`DerivedMetric`
and/or :class:`MeasurementsCsv` objects that have been derived from the
input. The exact nature and ordering of the list memebers is specific to
indivial 'class'`DerivedMeasurements` implewmentations.

The arguents to this method should be paths to raw output files generated by
an instrument. The number and order of expected arguments is specific to
particular implmentations.

Derived Metric
~~~~~~~~~~~~~~

.. class:: DerivedMetric

Represents a metric derived from previously collected ``Measurement``s.
Unlike, a ``Measurement``, this was not measured directly from the target.

.. attribute:: DerivedMetric.name

The name of the derived metric. This uniquely defines a metric -- two
``DerivedMetric`` objects with the same ``name`` represent to instances of
the same metric (e.g. computed from two different inputs).

.. attribute:: DerivedMetric.value

The ``numeric`` value of the metric that has been computed for a particular
input.

.. attribute:: DerivedMetric.measurement_type

The ``MeasurementType`` of the metric. This indicates which conceptual
category the metric falls into, its units, and conversions to other
measurement types.

.. attribute:: DerivedMetric.units

The units in which the metric's value is expressed.

Available Derived Measurements
-------------------------------

.. note:: If a method of the API is not documented for a particular
implementation, that means that it s not overriden by that
implementation. It is still safe to call it -- an empty list will be
returned.

Energy
~~~~~~

.. class:: DerivedEnergyMeasurements

The ``DerivedEnergyMeasurements`` class is used to calculate average power and
cumulative energy for each site if the required data is present.

The calculation of cumulative energy can occur in 3 ways. If a
``site`` contains ``energy`` results, the first and last measurements are extracted
and the delta calculated. If not, a ``timestamp`` channel will be used to calculate
the energy from the power channel, failing back to using the sample rate attribute
of the :class:`MeasurementCsv` file if timestamps are not available. If neither
timestamps or a sample rate are available then an error will be raised.

.. method:: DerivedEnergyMeasurements.process(measurement_csv)

This will return total cumulative energy for each energy channel, and the
average power for each power channel in the input CSV. The output will contain
all energy metrics followed by power metrics. The ordering of both will match
the ordering of channels in the input. The metrics will by named based on the
sites of the coresponding channels according to the following patters:
``"<site>_total_energy"`` and ``"<site>_average_power"``.

FPS / Rendering
~~~~~~~~~~~~~~~

.. class:: DerivedGfxInfoStats(drop_threshold=5, suffix='-fps', filename=None, outdir=None)

Produces FPS (frames-per-second) and other dervied statistics from
:class:`GfxInfoFramesInstrument` output. This takes several optional
parameters in creation:

:param drop_threshold: FPS in an application, such as a game, which this
processor is primarily targeted at, cannot reasonably
drop to a very low value. This is specified to this
threhold. If an FPS for a frame is computed to be
lower than this treshold, it will be dropped on the
assumption that frame rednering was suspended by the
system (e.g. when idling), or there was some sort of
error, and therefore this should be used in
performance calculations. defaults to ``5``.
:param suffix: The name of the gerated per-frame FPS csv file will be
derived from the input frames csv file by appending this
suffix. This cannot be specified at the same time as
a ``filename``.
:param filename: As an alternative to the suffix, a complete file name for
FPS csv can be specified. This cannot be used at the same
time as the ``suffix``.
:param outdir: By default, the FPS csv file will be placed in the same
directory as the input frames csv file. This can be changed
by specifying an alternate directory here

.. warning:: Specifying both ``filename`` and ``oudir`` will mean that exactly
the same file will be used for FPS output on each invocation of
``process()`` (even for different inputs) resulting in previous
results being overwritten.

.. method:: DerivedGfxInfoStats.process(measurement_csv)

Process the fames csv generated by :class:`GfxInfoFramesInstrument` and
returns a list containing exactly three entries: :class:`DerivedMetric`\ s
``fps`` and ``total_frames``, followed by a :class:`MeasurentCsv` containing
per-frame FPSs values.

.. method:: DerivedGfxInfoStats.process_raw(gfxinfo_frame_raw_file)

As input, this takes a single argument, which should be the path to the raw
output file of :class:`GfxInfoFramesInstrument`. The returns stats
accumulated by gfxinfo. At the time of wrinting, the stats (in order) are:
``janks``, ``janks_pc`` (percentage of all frames),
``render_time_50th_ptile`` (50th percentile, or median, for time to render a
frame), ``render_time_90th_ptile``, ``render_time_95th_ptile``,
``render_time_99th_ptile``, ``missed_vsync``, ``hight_input_latency``,
``slow_ui_thread``, ``slow_bitmap_uploads``, ``slow_issue_draw_commands``.
Please see the `gfxinfo documentation`_ for details.

.. _gfxinfo documentation: https://developer.android.com/training/testing/performance.html

.. class:: DerivedSurfaceFlingerStats(drop_threshold=5, suffix='-fps', filename=None, outdir=None)

Produces FPS (frames-per-second) and other dervied statistics from
:class:`SurfaceFlingerFramesInstrument` output. This takes several optional
parameters in creation:

.. method:: DerivedSurfaceFlingerStats.process(measurement_csv)

Process the fames csv generated by :class:`SurfaceFlingerFramesInstrument` and
returns a list containing exactly three entries: :class:`DerivedMetric`\ s
``fps`` and ``total_frames``, followed by a :class:`MeasurentCsv` containing
per-frame FPSs values, followed by ``janks`` ``janks_pc``, and
``missed_vsync`` metrics.