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<li class="toctree-l3"><a class="reference internal" href="../accessibility/coding-guidelines.html">Coding Guidelines for Supporting Accessibility</a></li>
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<li class="toctree-l3"><a class="reference internal" href="../localization/practices.html">Best Practices for Localization</a></li>
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<li class="toctree-l3"><a class="reference internal" href="../maintainer/api-stability.html">API Stability</a></li>
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<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/getting_started/content_view.html">Adding A Content View</a></li>
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<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/getting_started/saving_state.html">Saving The Application State</a></li>
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<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/getting_started/dark_mode.html">Forcing The Dark Color Scheme</a></li>
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|
<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/components/radio_button.html">Radio Buttons</a></li>
|
|||
|
|
<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/components/spin_button.html">Spin Buttons</a></li>
|
|||
|
|
<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/components/link_button.html">Link Buttons</a></li>
|
|||
|
|
<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/components/switch.html">Switches</a></li>
|
|||
|
|
<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/components/menu_button.html">Menu Buttons</a></li>
|
|||
|
|
<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/components/entry.html">Entries</a></li>
|
|||
|
|
<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/components/password_entry.html">Password Entries</a></li>
|
|||
|
|
<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/components/message_dialog.html">Messages</a></li>
|
|||
|
|
<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/components/file_dialog.html">File Dialogs</a></li>
|
|||
|
|
<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/components/spinner.html">Spinners</a></li>
|
|||
|
|
<li class="toctree-l4"><a class="reference internal" href="../../tutorials/beginners/components/level_bar.html">Level Bars</a></li>
|
|||
|
|
</ul>
|
|||
|
|
</li>
|
|||
|
|
</ul>
|
|||
|
|
</li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/application-id.html">Application ID</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/application.html">Using GtkApplication</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/save-state.html">Saving and Loading Window State</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/notifications.html">Using Notifications</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/themed-icons.html">Themed Icons</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/deprecations.html">Dealing With Deprecations</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/actions.html">Actions</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/menus.html">Menus</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/search-provider.html">Writing a Search Provider</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/pre-and-post-conditions.html">Pre- and Post-Conditions</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/main-contexts.html">Main Contexts</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/lists.html">Using GLib Lists</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/threading.html">Threading</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/asynchronous-programming.html">Asynchronous Programming</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/drag-and-drop.html">Drag and Drop</a></li>
|
|||
|
|
<li class="toctree-l2"><a class="reference internal" href="../../tutorials/widget-templates.html">Widget Templates</a></li>
|
|||
|
|
</ul>
|
|||
|
|
</li>
|
|||
|
|
</ul>
|
|||
|
|
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
</div>
|
|||
|
|
</aside>
|
|||
|
|
<main class="main">
|
|||
|
|
<div class="content">
|
|||
|
|
<article role="main">
|
|||
|
|
<label class="toc-overlay-icon toc-content-icon" for="__toc">
|
|||
|
|
<i class="icon"><svg><use href="#svg-toc"></use></svg></i>
|
|||
|
|
</label>
|
|||
|
|
<section id="optimizing-gnome-applications">
|
|||
|
|
<h1>Optimizing GNOME Applications<a class="headerlink" href="#optimizing-gnome-applications" title="Permalink to this headline">#</a></h1>
|
|||
|
|
<section id="what-are-we-optimizing">
|
|||
|
|
<h2>What are we optimizing?<a class="headerlink" href="#what-are-we-optimizing" title="Permalink to this headline">#</a></h2>
|
|||
|
|
<p>When we optimize for GNOME the first thing to remember is this: we are not
|
|||
|
|
trying to make the program better, we are trying to make the person using the
|
|||
|
|
computer happier.</p>
|
|||
|
|
<p>Better programs make people happier, but there are some improvements that will
|
|||
|
|
make them a lot happier than others: Responsiveness, start-up time, easy to
|
|||
|
|
access commands and not having the computer go into swap the moment more than
|
|||
|
|
two programs are open.</p>
|
|||
|
|
<p>Traditional optimization tackles concepts like CPU use, code size, the number of
|
|||
|
|
mouse clicks and the memory use of the program. This second list has been chosen
|
|||
|
|
to correlate with the first list, however there is an important difference: the
|
|||
|
|
person using GNOME doesn’t care about the second list, but they care a lot about
|
|||
|
|
the first list. When optimizing GNOME programs we will reduce CPU use, memory
|
|||
|
|
use and all those things, but these are the means to the end, not the final
|
|||
|
|
goal. We are optimizing for people.</p>
|
|||
|
|
</section>
|
|||
|
|
<section id="optimization">
|
|||
|
|
<h2>Optimization<a class="headerlink" href="#optimization" title="Permalink to this headline">#</a></h2>
|
|||
|
|
<p>The previous section omitted one important qualifier: to optimize something it
|
|||
|
|
has to be measurable. You can’t measure happiness. However, you can measure
|
|||
|
|
start-up time so you can tell if you have improved it. Happiness will then,
|
|||
|
|
hopefully, follow.</p>
|
|||
|
|
<p>Optimization is the process of measurement, refinement and re-measurement. So
|
|||
|
|
the first thing you must do is find a way to measure what you are optimizing.
|
|||
|
|
Ideally this measurement is a single number, for example: the time taken to
|
|||
|
|
perform a task. This is your benchmark, it is the only way to tell if you are
|
|||
|
|
winning or losing. There is a big difference between a program that should be
|
|||
|
|
fast and a program that is fast.</p>
|
|||
|
|
<p>Once you have a basic benchmark you need to find out why your code is not doing
|
|||
|
|
as well as it should. It is tempting to do this by inspection: just looking at
|
|||
|
|
the code and trying to spot something that looks like it needs improvement. You
|
|||
|
|
will invariably be wrong. Using a profiler to get a detailed break-down of what
|
|||
|
|
your program really does is the only way to be sure.</p>
|
|||
|
|
<p>Usually the problem is isolated to small sections of code. Pick the worst place
|
|||
|
|
and concentrate on that first. Once that is done, rerun the profiler and repeat.
|
|||
|
|
As you proceed the gains made at each step will get less and less, at some point
|
|||
|
|
you will have to decide that the results are good enough. If your efforts are
|
|||
|
|
only extracting 10% improvements then you are well past the point where you
|
|||
|
|
should have stopped.</p>
|
|||
|
|
<p>Don’t forget the big picture. For example, rather than just trying to speed up a
|
|||
|
|
piece of code, ask yourself if it needs to be run at all. Could it be combined
|
|||
|
|
with another piece of code? Can the results of previous calculations be saved
|
|||
|
|
and reused? It won’t even need to be optimized if it is in a place where the
|
|||
|
|
user is never going to notice it. Worse still, the code may already be optimized
|
|||
|
|
and is doing the heavy calculations now to avoid doing them later. Code does not
|
|||
|
|
run in isolation and neither does the optimization process.</p>
|
|||
|
|
</section>
|
|||
|
|
<section id="hints">
|
|||
|
|
<h2>Hints<a class="headerlink" href="#hints" title="Permalink to this headline">#</a></h2>
|
|||
|
|
<section id="the-fundamentals">
|
|||
|
|
<h3>The fundamentals<a class="headerlink" href="#the-fundamentals" title="Permalink to this headline">#</a></h3>
|
|||
|
|
<p>1. Re-run your benchmark after every change you make to the code and keep a log
|
|||
|
|
of everything you change and how it affects the benchmark. This lets you undo
|
|||
|
|
mistakes and also helps you not to repeat mistakes.</p>
|
|||
|
|
<p>2. Make sure your code is correct and bug-free before optimizing it. Check that
|
|||
|
|
it remains correct and bug-free after optimization.</p>
|
|||
|
|
<ol class="arabic simple" start="3">
|
|||
|
|
<li><p>Optimize at the high level before optimizing the details.</p></li>
|
|||
|
|
</ol>
|
|||
|
|
<p>4. Use the right algorithm. The classic text-book example is using quick-sort
|
|||
|
|
instead of bubble-sort. There are many others, some save memory, some save CPU.
|
|||
|
|
Also, see what shortcuts you can make: you can do quicker than quick-sort if you
|
|||
|
|
are prepared to make some compromises.</p>
|
|||
|
|
<p>5. Optimization is a trade-off. Caching results speeds up calculations, but
|
|||
|
|
increases memory use. Saving data to disk saves memory, but costs time when it
|
|||
|
|
is loaded back from disk.</p>
|
|||
|
|
<p>6. Make sure you choose a wide variety of inputs to optimize against. If you
|
|||
|
|
don’t it is easy to end up with a piece of code carefully optimized for one file
|
|||
|
|
and no others.</p>
|
|||
|
|
<p>7. Avoid expensive operations: Multiple small disk reads. Using up lots of
|
|||
|
|
memory so disk swapping becomes necessary. Avoid anything that writes or reads
|
|||
|
|
from the hard disk unnecessarily. The network is slow too. Also avoid graphics
|
|||
|
|
operations that need a response from the X server.</p>
|
|||
|
|
</section>
|
|||
|
|
<section id="traps-for-the-unwary">
|
|||
|
|
<h3>Traps for the unwary<a class="headerlink" href="#traps-for-the-unwary" title="Permalink to this headline">#</a></h3>
|
|||
|
|
<p>1. Beware of side effects. There can often be strange interactions between
|
|||
|
|
different sections of code, a speed-up in one part can slow another part down.</p>
|
|||
|
|
<p>2. When timing code, even on a quiet system, events outside the program add
|
|||
|
|
noise to the timing results. Average over multiple runs. If the code is very
|
|||
|
|
short, timer resolution is also a problem. In this case measure the time the
|
|||
|
|
computer takes to run the code 100 or 1000 times. If the times you are recording
|
|||
|
|
are longer than a few seconds, you should be OK.</p>
|
|||
|
|
<p>3. It is very easy to be misled by the profiler. There are stories of people
|
|||
|
|
optimizing the operating system idle-loop because that is where it spent all its
|
|||
|
|
time! Don’t optimize code that does nothing the user cares about.</p>
|
|||
|
|
<p>4. Remember the resources on the X server. Your program’s memory usage doesn’t
|
|||
|
|
include the pixmaps that are stored in the X server’s process, but they are
|
|||
|
|
still using up memory. Use xrestop to see what resources your program is using.</p>
|
|||
|
|
</section>
|
|||
|
|
<section id="low-level-hints">
|
|||
|
|
<h3>Low level hints<a class="headerlink" href="#low-level-hints" title="Permalink to this headline">#</a></h3>
|
|||
|
|
<p>1. When optimizing memory use, be wary of the difference between peak usage and
|
|||
|
|
average memory usage. Some memory is almost always allocated, this is usually
|
|||
|
|
bad. Some is only briefly allocated, this may be quite acceptable. Tools like
|
|||
|
|
massif use the concept of space-time, the product of memory used and the
|
|||
|
|
duration it was allocated for, instead.</p>
|
|||
|
|
<p>2. Time simplified bits of code that do only the things you know are essential,
|
|||
|
|
this gives an absolute lower limit on the time your code will take. For example,
|
|||
|
|
when optimizing a loop time the empty loop. If that is still too long no amount
|
|||
|
|
of micro-optimization will help and you will have to change your design. Make
|
|||
|
|
sure the compiler doesn’t optimize away your empty loop.</p>
|
|||
|
|
<p>3. Move code out from inside loops. A slightly more complicated piece of code
|
|||
|
|
that is executed once is far quicker than a simple piece of code executed a
|
|||
|
|
thousand times. Avoid calling slow code often.</p>
|
|||
|
|
<p>4. Give the compiler as many hints as possible. Use the const keyword. Use
|
|||
|
|
<code class="docutils literal notranslate"><span class="pre">G_INLINE_FUNC</span></code> for short, frequently called, functions. Look up
|
|||
|
|
<code class="docutils literal notranslate"><span class="pre">G_GNUC_PURE</span></code>, <code class="docutils literal notranslate"><span class="pre">G_LIKELY</span></code> and the other GLib miscellaneous macros. Use the
|
|||
|
|
macros instead of compiler-specific keywords to ensure portability.</p>
|
|||
|
|
<p>5. Don’t use assembly language. It is not portable and, while it may be fast on
|
|||
|
|
one processor, it is not even guaranteed to be fast on every processor that
|
|||
|
|
supports that architecture.</p>
|
|||
|
|
<p>6. Don’t rewrite an existing library routine unless you are sure it is
|
|||
|
|
unnecessarily slow. Many CPU-intensive library routines have already been
|
|||
|
|
optimized. Conversely, some library routines are slow, especially ones that make
|
|||
|
|
system calls to the operating system.</p>
|
|||
|
|
<p>7. Minimize the number of libraries you link to. The fewer libraries to link in,
|
|||
|
|
the faster the program starts. This can be a difficult thing to do with GNOME.</p>
|
|||
|
|
</section>
|
|||
|
|
<section id="high-level-tricks">
|
|||
|
|
<h3>High level tricks<a class="headerlink" href="#high-level-tricks" title="Permalink to this headline">#</a></h3>
|
|||
|
|
<p>1. Take advantage of concurrency. This doesn’t just mean using multiple
|
|||
|
|
processors, it also means taking advantage of the time the user spends thinking
|
|||
|
|
about what they are going to do next to perform some calculations in
|
|||
|
|
anticipation. Do calculations while waiting for data to be loaded off disk. Take
|
|||
|
|
advantage of multiple resources, use them all at once.</p>
|
|||
|
|
<p>2. Cheat. The user only has to think that the computer is fast, it doesn’t
|
|||
|
|
matter whether it actually is or not. It is the time between the command and the
|
|||
|
|
answer that is important, it doesn’t matter if the response is pre-calculated,
|
|||
|
|
cached, or will in fact be worked out later at a more convenient time, as long
|
|||
|
|
as the user gets what they expect.</p>
|
|||
|
|
<p>3. Do things in the idle loop. It is easier to program than using full
|
|||
|
|
multi-threading but still gets things done out of the users eye. Be careful
|
|||
|
|
though, if you spend too long in the idle loop your program will become
|
|||
|
|
sluggish. So regularly give control back to the main loop.</p>
|
|||
|
|
<p>4. If all else fails, tell the user that the code is going to be slow and put up
|
|||
|
|
a progress bar. They won’t be as happy as if you had just presented the results,
|
|||
|
|
but they will at least know the program hasn’t crashed and they can go get a cup
|
|||
|
|
of coffee.</p>
|
|||
|
|
</section>
|
|||
|
|
</section>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
</article>
|
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<footer>
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<div class="related-pages">
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<span>Next</span>
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Contents
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</div>
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<div class="toc-tree-container">
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|
|
<div class="toc-tree">
|
|||
|
|
<ul>
|
|||
|
|
<li><a class="reference internal" href="#">Optimizing GNOME Applications</a><ul>
|
|||
|
|
<li><a class="reference internal" href="#what-are-we-optimizing">What are we optimizing?</a></li>
|
|||
|
|
<li><a class="reference internal" href="#optimization">Optimization</a></li>
|
|||
|
|
<li><a class="reference internal" href="#hints">Hints</a><ul>
|
|||
|
|
<li><a class="reference internal" href="#the-fundamentals">The fundamentals</a></li>
|
|||
|
|
<li><a class="reference internal" href="#traps-for-the-unwary">Traps for the unwary</a></li>
|
|||
|
|
<li><a class="reference internal" href="#low-level-hints">Low level hints</a></li>
|
|||
|
|
<li><a class="reference internal" href="#high-level-tricks">High level tricks</a></li>
|
|||
|
|
</ul>
|
|||
|
|
</li>
|
|||
|
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</ul>
|
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</li>
|
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</ul>
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