[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 #8 from Dhananjay Ugwekar (AMD) (Dhananjay.Ugwekar@amd.com) ---
(In reply to Artem S. Tashkinov from comment #7)
> (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.

Right, this will be helpful, will put out a patch for this. Also there is an
"energy_performance_available_preferences" file which shows the allowed EPP
hints that can be written to the "energy_performance_preference" sysfs file,
you could incorporate that into your shell script.

> 
> 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

I guess you are using amd_pstate=active, in which only performance and
powersave governors are supported and the decision making is mostly in the
hands of platform firmware.

However, if you use amd_pstate=passive mode, the OS governors (schedutil,
conservative, etc) are responsible for making the frequency decisions.

 in which case I don't
> understand why they are exposed/exist in the first place.

Didnt understand this part, in which scenario were you able to see the
governors, but they were ineffective?

 Is it possible to
> hide them? Make them read only? Just to avoid further useless bug reports.

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are the assignee for the bug.