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CentOS7中CPU頻率調整問題


2022年5月01日
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cpufreq使用了新的intel_pstate驅動造成的困惑,詳細解答在這裏
Take a look at this discussion:
https://plus.google.com/117091380454742934025/posts/2vEekAsG2QT
1. intel_pstate can be disabled at boot-time with intel_pstate=disable or compile it out
2. the old problem with ondemand (and conservative) governors is and was, that they don't know the specific capabilities of the cpu
3. executing some tasks with highest-frequency possible is consuming less power, than taking more time with lower frequency e.g. arithmetic stuff
4. this is not true for all tasks e.g. loading something from main-memory
5. here comes intel_pstate: it knows how the specific cpu works and does it job better than a generic solution, also it seems to handle "boost" better
6. furthermore intel_pstate offers only two governors: powersave and performance
even "powersave" is faster than the generic acpi based approach with "performance" (maybe handles "boost" better)
also "performance" doesn't enforce the default frequency as "lower limit", like the old generic approch, but performance is anyway only ~ 1% faster
You can still select between these two governors with "cpupower frequency-set -g powersave/performance".
Run CPU with fixed frequency
Your good right. You paid for it! There are some good reasons for this:
Requirement of 100% reliable performance and answer-times
Bbenchmarking/Comparsion
Stress-Testing e.g. is CPU never throttled with your provided cooling solution
That is simple, set intel_pstate=disable at boot or remove it from your self compiled kernel. Now you can use the old generic acpi-based generic governors.
Or: Switch Powersave/Boost off in your BIOS/UEFI. This is what I do on desktops.
I will stay with intel_pstate and the default governor "powersave". It seems to do a good job at power-saving and my ThinkPad even runs faster smile
Maybe it would be less confusing if intel_pstate also overs a "fixed" governor which forces the default-frequencies. But this is merely "intel_pstate=disable".

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