View source for How To Profile QML App on Embedded Device

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[[Category:HowTo]]
[[Category:HowTo::Qt_Embedded]]

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= How to profile QML app on embedded device =

Information on profiling QML app is scattered in places so I thought of putting it together in one place.

== Prerequisite ==

NOTE: Assumption is that Linux PC is used as development environment
* Qt for host PC is installed. This is required to launch QtCreator
* Make sure that option "-no-declarative-debug" was NOT specified when configuring Qt for target device
* if Qt for target was configured with ''-prefix <installation-path>'' then make sure that same installation path exists on target
e.g. ''-prefix /usr/local/qt-48x-emb'' is specified then copy contents of ''/usr/local/qt-48x-emb'' from host to target at ''/usr/local/qt-48x-emb''
* Make sure Qt for target was built using same toolchain that will be used to build the app
* Host PC (which will be running QtCreator) and target should be on same network
NOTE:

== Profiling ==

At high level, to profile a QML app one will require to carry out following steps,
# Build the QML app to be profiled for target device
# Launch QML Profiler (external) from QtCreator on host
# Launch QML app on target with commandline options to enable remote profiling

=== Steps for building app ===

# Make sure that following options are added to the application's .pro file
<code>DEFINES ''= QMLJSDEBUGGER
DEFINES''= QT_DECLARATIVE_DEBUG
CONFIG += declarative_debug</code>
# Ensure QTDIR refers to the installation path of QT for target as specified in _-prefix_
<code>e.g. QTDIR=/usr/local/qt-48x-emb<code>
# Ensure PATH contains path of ''bin'' folder from installation path of Qt for target
</code>e.g. PATH=/usr/local/qt-48x-emb/bin:$PATH</code>
# Generate make file using the .pro
<code>host-cmd-prmt> qmake app.pro<code>
# Build the app
</code>host-cmd-prmt> make</code>
# Transfer the app binaries and necessary app files to the target

=== Launch QML Profiler (external) on host ===
# Launch QtCreator on host PC
# From the menu bar in QtCreator, select menu item '''''Analyze'''''-> '''''QML Profiler (External)'''''; this will popup a small dialog
# Note the '''''port''''' value. It will be passed on as command line option when launching the app
# Detail instructions on profiling and interpreting the results can be found [http://doc.qt.io/qtcreator-2.7/creator-qml-performance-monitor.html here]
# Hit the ''OK'' button after you launch the app on target

=== Launch the app to be profiled on the target ===

# Start the app on the target as,
<code>target-prmt> app -platform eglfs -qmljsdebugger=port:3456<code>

* Port value shall be same as that in the QML Profiler (External) Dialog
* the app is run against eglfs platform plugin but it could run against any other platform plugin if that is tested to be run on the target.

== Troubleshooting ==

=== Qt libraries not found ===

* Make sure Qt libraries are copied on the target
* export LD_LIBRARY_PATH to refer to the path where Qt libraries are copied
</code>e.g. LD_LIBRARY_PATH=/usr/local/qt-48x-emb/lib:$LD_LIBRARY_PATH</code>

=== Remote debugger plugin NOT found ===

* Confirm if following libraries were built for target,
<code>libqmldbg_tcp.so
libqmldbg_inspector.so</code>
* On target, these libraries should be present in /usr/local/qt-48x-emb/plugins/qmltooling
* export LD_LIBRARY_PATH to refer to the path where Qt plugin libraries are copied
<code>e.g. LD_LIBRARY_PATH=/usr/local/qt-48x-emb/plugins/qmltooling:$LD_LIBRARY_PATH<code>

=== Cannot capture the logs on host in QML profiler ===

* Make sure you synchronize launching of the app on target and starting the profiling on host PC.