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

[Elia Devito]

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@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.
> 
> 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