[Bug 219332] /sys/devices/system/cpu/cpufreq/policy0/energy_performance_preference: Device or resource busy

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=219332

--- Comment #7 from Artem S. Tashkinov (aros@gmx.com) ---
(In reply to Dhananjay Ugwekar (AMD) from comment #6)
> 
> I see from the attachment that you are using performance governor, so you
> are limited to only performance EPP hint, trying to write other EPP hints
> (power/balance_power/balance_performance) will show the above error. 
> 
> You'll need to change to powersave governor to use these hints. Please let
> me know if this fixes your issue.

That's indeed the case and changing the CPU frequency governor to "powersave"
has fixed the issue but I wonder if you could log an error message in dmesg if
the governor is incompatible with what the user has requested.

It still makes my head hurt trying to understand the interaction between
classic CPU governors and energy_performance_preference modes.

From the testing I've done it looks like classic CPU governors are 100%
useless/have zero effect in the presence of amd-pstate in which case I don't
understand why they are exposed/exist in the first place. Is it possible to
hide them? Make them read only? Just to avoid further useless bug reports.

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