Re: [RFC] Documentation: Add documentation for new performance_profile sysfs class (Also Re: [PATCH 0/4] powercap/dtpm: Add the DTPM framework)

[Hans de Goede]

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@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx
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 ?

Regards,

Hans