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<base href="https://bugzilla.gnome.org/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - GTK+ uses a lot more CPU under Wayland than under X11"
href="https://bugzilla.gnome.org/show_bug.cgi?id=772075">772075</a>
</td>
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<th>Summary</th>
<td>GTK+ uses a lot more CPU under Wayland than under X11
</td>
</tr>
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<th>Classification</th>
<td>Platform
</td>
</tr>
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<th>Product</th>
<td>gtk+
</td>
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<th>Version</th>
<td>3.21.x
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>Normal
</td>
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<th>Component</th>
<td>Backend: Wayland
</td>
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<th>Assignee</th>
<td>gtk-bugs@gtk.org
</td>
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<th>Reporter</th>
<td>gns@gnome.org
</td>
</tr>
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<th>QA Contact</th>
<td>gtk-bugs@gtk.org
</td>
</tr>
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<th>CC</th>
<td>rob@robster.org.uk, wayland-bugs@lists.freedesktop.org
</td>
</tr>
<tr>
<th>GNOME version</th>
<td>---
</td>
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<p>
<div>
<pre>When I run gtk3-demo --run=pixbufs on my Gnome on Wayland session I get around
86% CPU usage. If I run it with GDK_BACKEND=x11 it uses only around 25%.
Perf tells me the biggest offender is
bits_image_fetch_bilinear_affine_normal_a8. Setting a breakpoint in gdb I
noticed it is almost all due to gtk_window_draw drawing client-side
decorations, particularly shadows.
Returning at the top of that function after just chaining up to the parent
brings CPU usage down to ~42%. Still higher than under Xwayland, but much lower
than the original 86%.
This is the biggest drag on the WebKitGTK+ performance at the moment, I
believe. While playing a 4k video the browser spends most of its time painting
the window decoration.</pre>
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</p>
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