Message-ID: <7189685b-4975-ff09-8ac0-59f4e3204359@lenovo.com>
Date:   Mon, 19 Oct 2020 14:49:11 -0400
From:   Mark Pearson <markpearson@...ovo.com>
To:     Hans de Goede <hdegoede@...hat.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>
CC:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        "Srinivas Pandruvada ,>" <srinivas.pandruvada@...ux.intel.com>,
        "Lukasz Luba ,>" <lukasz.luba@....com>,
        "Linux Kernel Mailing List ,>" <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "> Zhang, Rui" <rui.zhang@...el.com>,
        Bastien Nocera <hadess@...ess.net>,
        "> Mark Pearson" <mpearson@...ovo.com>,
        "Limonciello, Mario ,>" <Mario.Limonciello@...l.com>,
        Darren Hart <dvhart@...radead.org>,
        "Andy ,> Shevchenko" <andy@...radead.org>,
        Mark Gross <mgross@...ux.intel.com>,
        "> Elia Devito" <eliadevito@...il.com>,
        Benjamin Berg <bberg@...hat.com>,
        "> linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "> platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>
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)

Hi

 > On 19/10/2020 14:43, Hans de Goede <hdegoede@...hat.com> wrote:
> Hi,
> 
> On 10/18/20 2:31 PM, Rafael J. Wysocki wrote:
>> On Sun, Oct 18, 2020 at 11:41 AM Hans de Goede <hdegoede@...hat.com> wrote:
>>>
>>> Hi,
>>>
>>> On 10/16/20 4:51 PM, Rafael J. Wysocki wrote:
>>>> On Fri, Oct 16, 2020 at 1:11 PM Hans de Goede <hdegoede@...hat.com> wrote:
>>>>>
>>>>> <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@...hat.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.
>>>>
>>>> Yes.
>>>>
>>>>> 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
>>>>
>>>> But this is not about energy vs performance only in general, is it?
>>>>
>>>>> (again only visible when applicable) ?
>>>>>
>>>>> I personally like the second option best.
>>>>
>>>> But I would put it under /sys/firmware/ instead of /sys/power/ and I
>>>> would call it something like platform_profile (and
>>>> platform_profile_choices or similar).
>>>
>>> Currently we only have dirs under /sys/firmware:
>>>
>>> [hans@x1 ~]$ ls /sys/firmware
>>> acpi  dmi  efi  memmap
>>>
>>> But we do have /sys/firmware/apci/pm_profile:
>>>
>>> Documentation/ABI/stable/sysfs-acpi-pmprofile
>>>
>>> What:           /sys/firmware/acpi/pm_profile
>>> Date:           03-Nov-2011
>>> KernelVersion:  v3.2
>>> Contact:        linux-acpi@...r.kernel.org
>>> Description:    The ACPI pm_profile sysfs interface exports the platform
>>>                 power management (and performance) requirement expectations
>>>                 as provided by BIOS. The integer value is directly passed as
>>>                 retrieved from the FADT ACPI table.
>>> Values:         For possible values see ACPI specification:
>>>                 5.2.9 Fixed ACPI Description Table (FADT)
>>>                 Field: Preferred_PM_Profile
>>>
>>>                 Currently these values are defined by spec:
>>>                 0 Unspecified
>>>                 1 Desktop
>>>                 2 Mobile
>>>                 3 Workstation
>>>                 4 Enterprise Server
>>>                 ...
>>>
>>> Since all platforms which we need this for are ACPI based
>>> (and the involved interfaces are also all ACPI interfaces)
>>> how about:
>>>
>>> /sys/firmware/acpi/platform_profile
>>> /sys/firmware/acpi/platform_profile_choices
>>>
>>> ?
>>>
>>> I think this goes nice together with /sys/firmware/acpi/pm_profile
>>> although that is read-only and this is a read/write setting.
>>>
>>> Rafel, would:
>>>
>>> /sys/firmware/acpi/platform_profile
>>> /sys/firmware/acpi/platform_profile_choices
>>>
>>> work for you ?
>> 
>> Yes, it would.
> 
> Great. So I think hat means that we have the most important part
> for moving forward with this.
> 
> So I guess the plan for this now looks something like this.
> 
> 1. Rewrite my API docs RFC to update it for the new 
> /sys/firmware/acpi/platform_profile[_choices]
>     plan (should be easy and a bunch of stuff like the "type" bit can 
> just be dropped)
> 
> 2. Add code somewhere under drivers/acpi which allows code from else where
>     to register itself as platform_profile handler/provider.
> 
> Rafael, any suggestions / preference for where this should be added under
> drivers/acpi ?  In a new .c file perhaps ?
> 
> 3.1 Use the code from 2 to add support for platform-profile selection in
>      thinkpad_acpi (something for me or Mark Pearson) to do
> 3.2 Use the code from 2 to add support for platform-profile selection
>      to hp-wmi
> 3.3 (and to other drivers in the future).
> 
> 
> An open question is who will take care of 1. and 2. Mark (Pearson)
> do you feel up to this? or do you want me to take care of this?
> 
> Regards,
> 
> Hans
> 

Definitely up for (2) and will happily have a go at number (1).

If there's an example of something similar I can look at for reference 
that would be helpful :)

Mark

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