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<p class="MsoNormal"><span style="font-size:11.0pt">Buglink: <a href="https://bugs.launchpad.net/ubuntu-realtime/+bug/1993326">
https://bugs.launchpad.net/ubuntu-realtime/+bug/1993326</a><o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="font-size:11.0pt;font-family:"Courier New";color:#333333"><o:p> </o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="font-size:11.0pt;color:black">SRU Justification:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">[Impact]<br>
With cppc_fie enabled, users can see 2% - 11% CPU overhead even when the system is idle. On real time kernel, cppc_fie leads to higher latencies up to 120 microseconds.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">The following patch:<br>
<a href="https://github.com/torvalds/linux/commit/ae2df912d1a557a3548be83da20851ac55f42ab3">https://github.com/torvalds/linux/commit/ae2df912d1a557a3548be83da20851ac55f42ab3</a><br>
fixes this issue by allowing users to disable cppc_fie at boot time.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">[Test Case]<br>
Running 'cyclictest' on an 80-core arm system with the following command:<br>
`sudo cyclictest -m -Sp90 -i200 -l100000 -h 400`<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Without the patch, the max latency reported is 121 us while with the patch the max latency is 20 us.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">[Regression Potential]<br>
This patch only affects the aarch64 architecture and is limited to the CPPC_CPUFREQ driver. Any regression is limited to this driver. From our testing, we find that there are no regressions by this patch.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">[Other Info]<br>
None<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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