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<base href="https://bugs.freedesktop.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Over 15% performance lost on large branching shader"
href="https://bugs.freedesktop.org/show_bug.cgi?id=110412">110412</a>
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<th>Summary</th>
<td>Over 15% performance lost on large branching shader
</td>
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<th>Product</th>
<td>Mesa
</td>
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<th>Version</th>
<td>git
</td>
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<th>Hardware</th>
<td>Other
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>medium
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<th>Component</th>
<td>Drivers/DRI/i965
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<th>Assignee</th>
<td>intel-3d-bugs@lists.freedesktop.org
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<th>Reporter</th>
<td>kevin.rogovin@intel.com
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<th>QA Contact</th>
<td>intel-3d-bugs@lists.freedesktop.org
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=143948" name="attach_143948" title="output from Mesa 18.2">attachment 143948</a> <a href="attachment.cgi?id=143948&action=edit" title="output from Mesa 18.2">[details]</a></span>
output from Mesa 18.2
A large branching shader suffers an over 15% performance loss comparing Mesa
GIT (revision a182adfd83ad00e326153b00a725a014e0359bf0) against Mesa 18.2.8 (on
Ubuntu 18.04).
To replicate,
1. Build painter-glyph-test-GL-debug from the project
<a href="https://github.com/intel/fastuidraw">https://github.com/intel/fastuidraw</a>
2. Run (adjusting width and height options to match ones monitor) with
vblank_mode=0 LD_LIBRARY_PATH=. ./painter-glyph-test-GL-release fullscreen
true width 1920 height 1200 use_file true text
demo_data/txt/wall_of_text_caps_no_numbers.txt
On my Iris Pro Graphics 580 (Skylake GT4e), I see (with fluctuations):
Mesa 18.2.8: 5.6 ms/frame [178 FPS]
a182adfd83ad00e326153b00a725a014e0359bf0: 6.5 ms/frame [153 FPS]
The shader being executed is a large uber-shader. In both tested Mesa's above,
the uber-shader is realized as only SIMD8 with no spilling.
Attached are the outputs when running with MESA_GLSL_CACHE_DISABLE=true
INTEL_DEBUG=fs for the offending fragment shader.</pre>
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