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133 lines
5.1 KiB
133 lines
5.1 KiB
13 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/qws.doc:532 -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>TQt/Embedded Performance Tuning</title>
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<font color="#004faf">Home</font></a>
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<font color="#004faf">All Classes</font></a>
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<font color="#004faf">Main Classes</font></a>
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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>TQt/Embedded Performance Tuning</h1>
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When building embedded applications on low-powered devices, a number
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of options are available that would not be considered in a desktop
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application environment. These options reduce the memory and/or CPU
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retquirements at the cost of other factors.
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<p> <ul>
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<li> <a href="emb-features.html"><b>Tuning the functionality of TQt</a>
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<li> <a href="#general">General programming style</a>
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<li> <a href="#static">Static vs. Dynamic linking</a>
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<li> <a href="#alloc">Alternative memory allocation</a>
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</ul>
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<p> <a name="general"></a>
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<h2> General programming style
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</h2>
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<a name="1"></a><p> The following guidelines will improve CPU performance:
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<ul>
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<li> Create dialogs and widgets once, then <a href="qwidget.html#hide">TQWidget::hide</a>() and
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<a href="qwidget.html#show">TQWidget::show</a>() them, rather than creating them and deleting
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them every time they are needed.
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This will use a little more memory, but will be much faster.
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Try to create them the first time "lazily" to avoid slow
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startup (e.g. only create a Find dialog the first time the
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user invokes it).
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</ul>
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<p> <a name="static"></a>
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<h2> Static vs. Dynamic linking
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</h2>
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<a name="2"></a><p> A lot of CPU and memory is used by the ELF linking process. You can
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make significant savings by using a static build of your application
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suite. This means that rather than having a dynamic library (<tt>libqte.so</tt>) and a collection of executables which link dynamically to
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that library, you build all the applications into a single executable
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and statically link that with a static library (<tt>libqt.a</tt>). This
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improves start-up time, and reduces memory usage, at the expense of
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flexibility (to add a new application, you must recompile the single
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executable) and robustness (if one application has a bug, it might
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harm other applications). If you need to install end-user
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applications, this may not be an option, but if you are building a
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single application suite for a device with limited CPU power and
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memory, this option could be very beneficial.
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<p> To compile TQt as a static library, add the <tt>-static</tt> options when
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you run configure.
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<p> To build your application suite as an all-in-one application, design each
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application as a stand-alone widget or set of widgets, with only minimal
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code in the main() function. Then, write an application that gives
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some way to switch between the applications (e.g. a <a href="qiconview.html">TQIconView</a>).
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<a href="http://www.trolltech.com/products/qtopia/index.html">TQtopia</a> is an example of this. It can be built either as a set of
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dynamically linked executables, or as a single static application.
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<p> Note that you should generally still link dynamically against the
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standard C library and any other libraries which might be used by
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other applications on your device.
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<p> <a name="alloc"></a>
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<h2> Alternative memory allocation
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</h2>
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<a name="3"></a><p> We have found that the libraries shipped with some C++ compilers on
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some platforms have poor performance in the built-in "new" and "delete"
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operators. You might gain performance by re-implementing these
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functions. For example, you can switch to the plain C allocators
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by adding the following to your code:
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<p> <pre>
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void* operator new[]( size_t size )
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{
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return malloc( size );
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}
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void* operator new( size_t size )
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{
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return malloc( size );
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}
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void operator delete[]( void *p )
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{
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free( p );
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}
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void operator delete[]( void *p, size_t size )
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{
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free( p );
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}
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void operator delete( void *p )
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{
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free( p );
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}
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void operator delete( void *p, size_t size )
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{
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free( p );
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}
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</pre>
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<!-- eof -->
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<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>TQt 3.3.8</div>
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</table></div></address></body>
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