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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Profile Instruction Generate/Coverage mapping: High overhead at runtime with many threads"
href="https://bugs.llvm.org/show_bug.cgi?id=35964">35964</a>
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<th>Summary</th>
<td>Profile Instruction Generate/Coverage mapping: High overhead at runtime with many threads
</td>
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<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>dennis.felsing@sap.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=19681" name="attach_19681" title="Source code">attachment 19681</a> <a href="attachment.cgi?id=19681&action=edit" title="Source code">[details]</a></span>
Source code
Creating coverage information with -fprofile-instr-generate -fcoverage-mapping
usually doesn't create a high overhead. When using dozens of threads the
overhead seems to grow significantly in the end running 24 times as slow with
40 threads. See the following table created on a 2x Intel E5-2660v3 system:
Threads No Coverage [s] Coverage [s] Factor
1 0.011 0.011 1.0
2 0.071 0.257 3.6
3 0.216 1.419 6.57
4 0.377 4.735 12.56
5 0.678 8.097 11.94
10 3.250 37.037 11.40
20 17.223 392.021 22.76
40 84.129 2087.047 24.81</pre>
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