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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - 10% perf drop in CPU bound tests with "i965: Call gen6_upload_push_constants() even when the stage is disabled""
href="https://bugs.freedesktop.org/show_bug.cgi?id=103517">103517</a>
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<th>Summary</th>
<td>10% perf drop in CPU bound tests with "i965: Call gen6_upload_push_constants() even when the stage is disabled"
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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
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
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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>eero.t.tamminen@intel.com
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<th>QA Contact</th>
<td>intel-3d-bugs@lists.freedesktop.org
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<p>
<div>
<pre>ezBench bisected following commit:
-------------------------------------------------------
commit 66b4a7a79e3da03e11233acd32b6e37bf3969dd8
Author: Kenneth Graunke <<a href="mailto:kenneth@whitecape.org">kenneth@whitecape.org</a>>
AuthorDate: Fri Oct 20 15:53:50 2017 -0700
Commit: Kenneth Graunke <<a href="mailto:kenneth@whitecape.org">kenneth@whitecape.org</a>>
CommitDate: Tue Oct 24 16:14:04 2017 -0700
i965: Call gen6_upload_push_constants() even when the stage is disabled.
This properly sets stage_state->push_constant_dirty = true, so that we
emit 3DSTATE_CONSTANT_XS to disable the constant buffer for the shader
stage. It also sets stage_state->push_const_size = 0.
Reviewed-by: Topi Pohjolainen <<a href="mailto:topi.pohjolainen@intel.com">topi.pohjolainen@intel.com</a>>
-------------------------------------------------------
As the cause for ~10% performance drop in following CPU bound 3D tests:
- GfxBench v4 Driver2 onscreen/offscreen
- SynMark v7 Batch6, Batch7 & Multithread
Most visible the drop was on SKL i5 6600K (it's never TDP limited), then SKL
GT4e & BDW GT2/GT3. On other platforms it's visible in trends, but impact is a
bit smaller and variance is too large to bisect it well.
There were no related performance improvements visible.
When looking at the system state before and after the change, main difference
is that CPU usage seems to have moved slightly from user-space to something
requested from kernel side, which makes sense for this commit.</pre>
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