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<p class="MsoNormal">Hi all,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’d like to discuss about the LLVM SW mitigation to Jump Conditional Code Erratum in this mailing thread. The patch was submitted in phabricator
<a href="https://reviews.llvm.org/D70157">https://reviews.llvm.org/D70157</a>. There were many review comments about its performance/code size impact, and some suggestions how to make the patches more generic to apply to other scenarios.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Let’s start from the performance/code size/build time impact. Below is the data we got from the test suite.<o:p></o:p></p>
<table class="MsoNormalTable" border="0" cellspacing="0" cellpadding="0" width="460" style="width:344.75pt;border-collapse:collapse">
<tbody>
<tr style="height:26.5pt">
<td width="162" nowrap="" rowspan="2" style="width:121.8pt;background:white;padding:0in 5.4pt 0in 5.4pt;height:26.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">LLVM test-suite<o:p></o:p></span></p>
</td>
<td width="64" nowrap="" colspan="2" rowspan="2" style="width:48.25pt;padding:0in 5.4pt 0in 5.4pt;height:26.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">Baseline<o:p></o:p></span></p>
</td>
<td width="72" rowspan="2" style="width:54.25pt;padding:0in 5.4pt 0in 5.4pt;height:26.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">sw_prefix<o:p></o:p></span></p>
</td>
<td width="63" rowspan="2" style="width:47.1pt;padding:0in 5.4pt 0in 5.4pt;height:26.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">hw<o:p></o:p></span></p>
</td>
<td width="98" rowspan="2" style="width:73.35pt;padding:0in 5.4pt 0in 5.4pt;height:26.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">hw_sw_prefix<o:p></o:p></span></p>
</td>
<td style="height:26.5pt;border:none" width="0" height="53"></td>
</tr>
<tr style="height:14.5pt">
<td style="height:14.5pt;border:none" width="0" height="29"></td>
</tr>
<tr style="height:14.5pt">
<td width="162" nowrap="" style="width:121.8pt;background:white;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">compile_time<o:p></o:p></span></p>
</td>
<td width="64" nowrap="" colspan="2" style="width:48.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">0.276<o:p></o:p></span></p>
</td>
<td width="72" nowrap="" style="width:54.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">0.282<o:p></o:p></span></p>
</td>
<td width="63" nowrap="" style="width:47.1pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">0.276<o:p></o:p></span></p>
</td>
<td width="98" nowrap="" style="width:73.35pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">0.282<o:p></o:p></span></p>
</td>
<td style="height:14.5pt;border:none" width="0" height="29"></td>
</tr>
<tr style="height:14.5pt">
<td width="162" nowrap="" style="width:121.8pt;background:white;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">exec_time<o:p></o:p></span></p>
</td>
<td width="64" nowrap="" colspan="2" style="width:48.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">286.465<o:p></o:p></span></p>
</td>
<td width="72" nowrap="" style="width:54.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">285.017<o:p></o:p></span></p>
</td>
<td width="63" nowrap="" style="width:47.1pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">291.294<o:p></o:p></span></p>
</td>
<td width="98" nowrap="" style="width:73.35pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">287.766<o:p></o:p></span></p>
</td>
<td style="height:14.5pt;border:none" width="0" height="29"></td>
</tr>
<tr style="height:14.5pt">
<td width="162" nowrap="" style="width:121.8pt;background:white;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">code_size<o:p></o:p></span></p>
</td>
<td width="64" nowrap="" colspan="2" style="width:48.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">3.868<o:p></o:p></span></p>
</td>
<td width="72" nowrap="" style="width:54.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">3.889<o:p></o:p></span></p>
</td>
<td width="63" nowrap="" style="width:47.1pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">3.868<o:p></o:p></span></p>
</td>
<td width="98" nowrap="" style="width:73.35pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">3.889<o:p></o:p></span></p>
</td>
<td style="height:14.5pt;border:none" width="0" height="29"></td>
</tr>
<tr style="height:14.5pt">
<td width="162" nowrap="" valign="bottom" style="width:121.8pt;background:white;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Times New Roman",serif;color:black"><o:p> </o:p></span></p>
</td>
<td width="64" nowrap="" colspan="2" valign="bottom" style="width:48.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Times New Roman",serif;color:black"><o:p> </o:p></span></p>
</td>
<td width="72" nowrap="" valign="bottom" style="width:54.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
</td>
<td width="63" nowrap="" valign="bottom" style="width:47.1pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
</td>
<td width="98" nowrap="" valign="bottom" style="width:73.35pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
</td>
<td style="height:14.5pt;border:none" width="0" height="29"></td>
</tr>
<tr style="height:26.5pt">
<td width="162" nowrap="" rowspan="2" style="width:121.8pt;background:white;padding:0in 5.4pt 0in 5.4pt;height:26.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">LLVM test-suite<o:p></o:p></span></p>
</td>
<td width="64" nowrap="" colspan="2" rowspan="2" style="width:48.25pt;padding:0in 5.4pt 0in 5.4pt;height:26.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">Baseline<o:p></o:p></span></p>
</td>
<td width="72" rowspan="2" style="width:54.25pt;padding:0in 5.4pt 0in 5.4pt;height:26.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">sw_prefix<o:p></o:p></span></p>
</td>
<td width="63" rowspan="2" style="width:47.1pt;padding:0in 5.4pt 0in 5.4pt;height:26.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">hw<o:p></o:p></span></p>
</td>
<td width="98" rowspan="2" style="width:73.35pt;padding:0in 5.4pt 0in 5.4pt;height:26.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">hw_sw_prefix<o:p></o:p></span></p>
</td>
<td style="height:26.5pt;border:none" width="0" height="53"></td>
</tr>
<tr style="height:14.5pt">
<td style="height:14.5pt;border:none" width="0" height="29"></td>
</tr>
<tr style="height:14.5pt">
<td width="162" nowrap="" style="width:121.8pt;background:white;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">compile_time<o:p></o:p></span></p>
</td>
<td width="64" nowrap="" colspan="2" style="width:48.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">1.000<o:p></o:p></span></p>
</td>
<td width="72" nowrap="" style="width:54.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">1.021<o:p></o:p></span></p>
</td>
<td width="63" nowrap="" style="width:47.1pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">1.000<o:p></o:p></span></p>
</td>
<td width="98" nowrap="" style="width:73.35pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">1.021<o:p></o:p></span></p>
</td>
<td style="height:14.5pt;border:none" width="0" height="29"></td>
</tr>
<tr style="height:14.5pt">
<td width="162" nowrap="" style="width:121.8pt;background:white;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">exec_time<o:p></o:p></span></p>
</td>
<td width="64" nowrap="" colspan="2" style="width:48.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">1.000<o:p></o:p></span></p>
</td>
<td width="72" nowrap="" style="width:54.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">0.995<o:p></o:p></span></p>
</td>
<td width="63" nowrap="" style="width:47.1pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">1.017<o:p></o:p></span></p>
</td>
<td width="98" nowrap="" style="width:73.35pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">1.005<o:p></o:p></span></p>
</td>
<td style="height:14.5pt;border:none" width="0" height="29"></td>
</tr>
<tr style="height:14.5pt">
<td width="162" nowrap="" style="width:121.8pt;background:white;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">code_size<o:p></o:p></span></p>
</td>
<td width="64" nowrap="" colspan="2" style="width:48.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">1.000<o:p></o:p></span></p>
</td>
<td width="72" nowrap="" style="width:54.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">1.005<o:p></o:p></span></p>
</td>
<td width="63" nowrap="" style="width:47.1pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">1.000<o:p></o:p></span></p>
</td>
<td width="98" nowrap="" style="width:73.35pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black">1.005<o:p></o:p></span></p>
</td>
<td style="height:14.5pt;border:none" width="0" height="29"></td>
</tr>
<tr style="height:14.5pt">
<td width="210" nowrap="" colspan="2" style="width:157.5pt;background:white;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Test date:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"> 2019/11/25<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">System Configuration:<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span lang="EN-GB">OS: Red Hat* 8.0 x86_64<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span lang="EN-GB">Memory: 191 GB<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span lang="EN-GB">CPUCount: 2<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span lang="EN-GB">CoreCount: 40<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span lang="EN-GB">Intel HyperThreading: yes<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span lang="EN-GB">CPU Model: Intel(R) Xeon(R) Gold 6148 CPU @ 2.40GHz<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span lang="EN-GB">Microcode w/o hw mitigation: 0x200005e<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span lang="EN-GB">Microcode with hw mitigation: 0x2000063<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
</td>
<td width="17" nowrap="" style="width:12.55pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black"><o:p> </o:p></span></p>
</td>
<td width="72" nowrap="" style="width:54.25pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black"><o:p> </o:p></span></p>
</td>
<td width="63" nowrap="" style="width:47.1pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black"><o:p> </o:p></span></p>
</td>
<td width="98" nowrap="" style="width:73.35pt;padding:0in 5.4pt 0in 5.4pt;height:14.5pt">
<p class="MsoNormal" align="center" style="text-align:center"><span style="color:black"><o:p> </o:p></span></p>
</td>
<td style="height:14.5pt;border:none" width="0" height="29"></td>
</tr>
<tr height="0">
<td width="244" style="border:none"></td>
<td width="71" style="border:none"></td>
<td width="25" style="border:none"></td>
<td width="109" style="border:none"></td>
<td width="94" style="border:none"></td>
<td width="147" style="border:none"></td>
<td style="border:none" width="0">
<p class="MsoNormal"> </p>
</td>
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</tbody>
</table>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoNormal" style="mso-list:l0 level1 lfo1;vertical-align:baseline"><i>Baseline
</i>means the system w/o MCU mitigation and w/o SW mitigation.<i><o:p></o:p></i></li><li class="MsoNormal" style="mso-list:l0 level1 lfo1;vertical-align:baseline"><i>SW_prefix
</i>means prefix mitigation is applied to a Non MCU system.<i><o:p></o:p></i></li><li class="MsoNormal" style="mso-list:l0 level1 lfo1;vertical-align:baseline"><i>HW</i> means the MCU mitigation is applied w/o SW mitigation.<o:p></o:p></li><li class="MsoNormal" style="mso-list:l0 level1 lfo1;vertical-align:baseline"><i>HW+SW</i> means both MCU and prefix mitigations are applied.<o:p></o:p></li><li class="MsoNormal" style="mso-list:l0 level1 lfo1;vertical-align:baseline">The data in 2<sup>nd</sup> table is normalized as the ratio vs. baseline. The smaller the better.<o:p></o:p></li><li class="MsoNormal" style="mso-list:l0 level1 lfo1;vertical-align:baseline">The test is done on an engineering build plus the SW mitigation patch. It may be variant from build to build. <o:p></o:p></li></ol>
<p class="MsoNormal" style="vertical-align:baseline"><o:p> </o:p></p>
<p class="MsoNormal" style="vertical-align:baseline">The data indicates that there’s some performance penalty (1.7%) in HW mitigation. And it reduced to 0.5% with prefix mitigated. The code size increase in test suite is about 0.5%. And the compile time increase
is about 2%. <o:p></o:p></p>
<p class="MsoNormal" style="vertical-align:baseline"><o:p> </o:p></p>
<p class="MsoNormal" style="vertical-align:baseline">More data will follow. <o:p>
</o:p></p>
<p class="MsoNormal" style="vertical-align:baseline"><o:p> </o:p></p>
<p class="MsoNormal" style="vertical-align:baseline"><span lang="EN-GB">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal" style="vertical-align:baseline"><span lang="EN-GB">Annita<o:p></o:p></span></p>
<p class="MsoNormal" style="vertical-align:baseline"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:12.0pt;font-family:"Times New Roman",serif">For more complete information about performance and benchmark results, visit </span><span lang="EN-GB"><a href="http://www.intel.com/benchmarks"><span style="font-size:12.0pt;font-family:"Times New Roman",serif">www.intel.com/benchmarks</span></a></span><span lang="EN-GB" style="font-size:12.0pt;font-family:"Times New Roman",serif">.
For specific information and notices/disclaimers regarding the Jump Conditional Code Erratum, visit </span><span lang="EN-GB"><a href="https://www.intel.com/content/dam/support/us/en/documents/processors/mitigations-jump-conditional-code-erratum.pdf"><span style="font-size:12.0pt;font-family:"Times New Roman",serif">https://www.intel.com/content/dam/support/us/en/documents/processors/mitigations-jump-conditional-code-erratum.pdf</span></a></span><span lang="EN-GB" style="font-size:12.0pt;font-family:"Times New Roman",serif">.<o:p></o:p></span></p>
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