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Subject: Re: Fw: [External] Re: [RFC] Documentation: Add documentation for new
 performance_profile sysfs class (Also Re: [PATCH 0/4] powercap/dtpm: Add the
 DTPM framework)
To:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Hans de Goede <hdegoede@redhat.com>,
        Elia Devito <eliadevito@gmail.com>
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CC:     aniel Lezcano <daniel.lezcano@linaro.org>,
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From:   Mark Pearson <markpearson@lenovo.com>
Message-ID: <f9163f54-9379-89f6-aaaf-e2d5084051df@lenovo.com>
Date:   Fri, 16 Oct 2020 10:43:09 -0400
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<Note - switched my email address to my more open source non-outlook 
based address>

On 2020-10-16 10:32 a.m., Mark Pearson wrote:
> 
> 
> ------------------------------------------------------------------------
> *From:* Elia Devito <eliadevito@gmail.com>
> *Sent:* October 16, 2020 10:26
> *To:* Rafael J. Wysocki <rafael@kernel.org>; Hans de Goede 
> <hdegoede@redhat.com>
> *Cc:* Daniel Lezcano <daniel.lezcano@linaro.org>; Srinivas Pandruvada 
> <srinivas.pandruvada@linux.intel.com>; Lukasz Luba 
> <lukasz.luba@arm.com>; Linux Kernel Mailing List 
> <linux-kernel@vger.kernel.org>; Linux PM <linux-pm@vger.kernel.org>; 
> Zhang, Rui <rui.zhang@intel.com>; Bastien Nocera <hadess@hadess.net>; 
> Mark Pearson <mpearson@lenovo.com>; Limonciello, Mario 
> <Mario.Limonciello@dell.com>; Darren Hart <dvhart@infradead.org>; Andy 
> Shevchenko <andy@infradead.org>; Mark Gross <mgross@linux.intel.com>; 
> Benjamin Berg <bberg@redhat.com>; linux-acpi@vger.kernel.org 
> <linux-acpi@vger.kernel.org>; platform-driver-x86@vger.kernel.org 
> <platform-driver-x86@vger.kernel.org>
> *Subject:* [External] Re: [RFC] Documentation: Add documentation for new 
> performance_profile sysfs class (Also Re: [PATCH 0/4] powercap/dtpm: Add 
> the DTPM framework)
> Hi,
> 
> In data venerdì 16 ottobre 2020 13:10:54 CEST, Hans de Goede ha scritto:
>> <note folding the 2 threads we are having on this into one, adding every one
>> from both threads to the Cc>
>> 
>> Hi,
>> 
>> On 10/14/20 5:42 PM, Rafael J. Wysocki wrote:
>> > On Wed, Oct 14, 2020 at 4:06 PM Hans de Goede <hdegoede@redhat.com> wrote:
>> >> On 10/14/20 3:33 PM, Rafael J. Wysocki wrote:
>> <snip>
>> 
>> >>> First, a common place to register a DPTF system profile seems to be
>> >>> needed and, as I said above, I wouldn't expect more than one such
>> >>> thing to be present in the system at any given time, so it may be
>> >>> registered along with the list of supported profiles and user space
>> >>> will have to understand what they mean.
>> >> 
>> >> Mostly Ack, I would still like to have an enum for DPTF system
>> >> profiles in the kernel and have a single piece of code map that
>> >> enum to profile names. This enum can then be extended as
>> >> necessary, but I want to avoid having one driver use
>> >> "Performance" and the other "performance" or one using
>> >> "performance-balanced" and the other "balanced-performance", etc.
>> >> 
>> >> With the goal being that new drivers use existing values from
>> >> the enum as much as possible, but we extend it where necessary.
>> > 
>> > IOW, just a table of known profile names with specific indices assigned to
>> > them.
>> Yes.
>> 
>> > This sounds reasonable.
>> > 
>> >>> Second, irrespective of the above, it may be useful to have a
>> >>> consistent way to pass performance-vs-power preference information
>> >>> from user space to different parts of the kernel so as to allow them
>> >>> to adjust their operation and this could be done with a system-wide
>> >>> power profile attribute IMO.
>> >> 
>> >> I agree, which is why I tried to tackle both things in one go,
>> >> but as you said doing both in 1 API is probably not the best idea.
>> >> So I believe we should park this second issue for now and revisit it
>> >> when we find a need for it.
>> > 
>> > Agreed.
>> > 
>> >> Do you have any specific userspace API in mind for the
>> >> DPTF system profile selection?
>> > 
>> > Not really.
>> 
>> So before /sys/power/profile was mentioned, but that seems more like
>> a thing which should have a set of fixed possible values, iow that is
>> out of scope for this discussion.
>> 
>> Since we all seem to agree that this is something which we need
>> specifically for DPTF profiles maybe just add:
>> 
>> /sys/power/dptf_current_profile    (rw)
>> /sys/power/dptf_available_profiles (ro)
>> 
>> (which will only be visible if a dptf-profile handler
>>  has been registered) ?
>> 
>> Or more generic and thus better (in case other platforms
>> later need something similar) I think, mirror the:
>> 
>> /sys/bus/cpu/devices/cpu#/cpufreq/energy_performance_* bits
>> for a system-wide energy-performance setting, so we get:
>> 
>> /sys/power/energy_performance_preference
>> /sys/power/energy_performance_available_preferences
>> 
>> (again only visible when applicable) ?
>> 
>> I personally like the second option best.
>> 
>> Regards,
>> 
>> Hans
> 
> between the two, the second seems to me more appropriate.
> Considering that the various profiles interact with thermal behaviors 
> what do
> you think of something like:
> 
> /sys/power/thermal_profile_available_profiles
> /sys/power/thermal_profile_profile
> 
> Regards,
> Elia
> 
I'm good with either but I do find 'profile_profile' slightly awkward to 
say out loud (even though it's logically correct :))

How about just:
/sys/power/platform_profile
/sys/power/platform_profile_available

As it covers the platform as a whole - fans, temperature, power, and 
anything else that ends up getting thrown in?

Mark