Linux 5.17 Will Have An Important Intel P-State Update For Alder Lake Mobile CPUs

Written by Michael Larabel in Intel on 22 December 2021 at 05:12 AM EST. 3 Comments
Linux 5.17 will have a seemingly important fix for upcoming Intel Alder Lake mobile processors. Without this change/fix, you might not see the advertised one-core turbo frequencies being met for your processor depending upon the system and whether tuning your EPP.

A change to the Intel P-State CPU frequency scaling driver is now queued up as part of the power management code destined for Linux 5.17. "There is an expectation from users that they can get frequency specified by cpufreq/cpuinfo_max_freq when conditions permit. But with AlderLake mobile it may not be possible," begins the patch with this Alder Lake mobile fix.

With upcoming Alder Lake mobile processors the Energy Performance Preference (EPP) value behaves slightly differently and with the existing kernel behavior could lead to the CPU frequencies potentially being limited. But the fix will update the EPP value at boot to try to limit clipping of frequencies. The EPP number ultimately impacts the rate of the performance state being increased/decreased depending upon performance/power-savings preferences of the system.

What this means from the driver side is an EPP value of 128 worked well for prior Intel CPU generations to ensure maximum frequencies can be reached while for Alder Lake mobile that value should be 102. A code comment also reinforces that an EPP value of 102 is the maximum suggested value that can result in one core turbo frequency being met for Alder Lake mobile CPUs.

So for Alder Lake mobile, P-State will set 102 on boot for the EPP while keeping to 128 for other CPUs in order to hopefully see better turbo behavior out-of-the-box for these processors under Linux. The EPP is tunable via sysfs by Linux users if desiring better performance or increasing the number for striving towards better power-savings while now at least for Alder Lake mobile the out-of-the-box behavior for balanced performance should at least see one core turbo frequencies being more likely to be achieved.
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