Re: [RFC] Documentation: Add documentation for new performance_profile sysfs class

[Hans de Goede]

Hi,

On 10/5/20 3:13 PM, Benjamin Berg wrote:
> Hi,
>
> seems reasonable to me. Quite simple, but likely good enough as we are
> sticking to only use well known names.
>
> Just found a small typo.
>
> Benjamin
>
> On Sat, 2020-10-03 at 15:19 +0200, Hans de Goede wrote:
> > On modern systems CPU/GPU/... performance is often dynamically configurable
> > in the form of e.g. variable clock-speeds and TPD. The performance is often
> > automatically adjusted to the load by some automatic-mechanism (which may
> > very well live outside the kernel).
> >
> > These auto performance-adjustment mechanisms often can be configured with
> > one of several performance-profiles, with either a bias towards low-power
> > consumption (and cool and quiet) or towards performance (and higher power
> > consumption and thermals).
> >
> > Introduce a new performance_profile class/sysfs API which offers a generic
> > API for selecting the performance-profile of these automatic-mechanisms.
> >
> > Cc: Mark Pearson <markpearson@xxxxxxxxxx>
> > Cc: Elia Devito <eliadevito@xxxxxxxxx>
> > Cc: Bastien Nocera <hadess@xxxxxxxxxx>
> > Cc: Benjamin Berg <bberg@xxxxxxxxxx>
> > Cc: linux-pm@xxxxxxxxxxxxxxx
> > Cc: linux-acpi@xxxxxxxxxxxxxxx
> > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> > ---
> >   .../testing/sysfs-class-performance_profile   | 104 ++++++++++++++++++
> >   1 file changed, 104 insertions(+)
> >   create mode 100644 Documentation/ABI/testing/sysfs-class-performance_profile
> >
> > diff --git a/Documentation/ABI/testing/sysfs-class-performance_profile b/Documentation/ABI/testing/sysfs-class-performance_profile
> > new file mode 100644
> > index 000000000000..9c67cae39600
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-class-performance_profile
> > @@ -0,0 +1,104 @@
> > +Performance-profile selection (e.g. /sys/class/performance_profile/thinkpad_acpi/)
> > +
> > +On modern systems CPU/GPU/... performance is often dynamically configurable
> > +in the form of e.g. variable clock-speeds and TPD. The performance is often
> > +automatically adjusted to the load by some automatic-mechanism (which may
> > +very well live outside the kernel).
> > +
> > +These auto performance-adjustment mechanisms often can be configured with
> > +one of several performance-profiles, with either a bias towards low-power
> > +consumption (and cool and quiet) or towards performance (and higher power
> > +consumption and thermals).
> > +
> > +The purpose of the performance_profile class is to offer a generic sysfs
> > +API for selecting the performance-profile of these automatic-mechanisms.
> > +
> > +Note that this API is only for selecting the performance-profile, it is
> > +NOT a goal of this API to allow monitoring the resulting performance
> > +characteristics. Monitoring performance is best done with device/vendor
> > +specific tools such as e.g. turbostat.
> > +
> > +Specifically when selecting a high-performance profile the actual achieved
> > +performance may be limited by various factors such as: the heat generated by
> > +other components, room temperature, free air flow at the bottom of a laptop,
> > +etc. It is explicitly NOT a goal of this API to let userspace know about
> > +any sub-optimal conditions which are impeding reaching the requested
> > +performance level.
> > +
> > +Since numbers are a rather meaningless way to describe performance-profiles
> > +this API uses strings to describe the various profiles. To make sure that
> > +userspace gets a consistent experience when using this API this API document
> > +defines a fixed set of profile-names. Drivers *must* map their internal
> > +profile representation/names onto this fixed set.
> > +
> > +If for some reason there is no good match when mapping then a new profile-name
> > +may be added. Drivers which wish to introduce new profile-names must:
> > +1. Have very good reasons to do so.
> > +2. Add the new profile-name to this document, so that future drivers which also
> > +   have a similar problem can use the same new. Usually new profile-names will
>
> Typo, "new" -> "name" I suppose.

Ack, fixed in my local tree.

Thx.

Regards,

Hans


> > +   be added to the "extra profile-names" section of this document. But in some
> > +   cases the set of standard profile-names may be extended.
> > +
> > +What:		/sys/class/performance_profile/<device>/available_profiles
> > +Date:		October 2020
> > +Contact:	Hans de Goede <hdegoede@xxxxxxxxxx>
> > +Description:
> > +		Reading this file gives a space separated list of profiles
> > +		supported for this device.
> > +
> > +		Drivers must use the following standard profile-names whenever
> > +		possible:
> > +
> > +		low-power:		Emphasises low power consumption
> > +					(and also cool and quiet)
> > +		balanced-low-power:	Balances between low power consumption
> > +					and performance with a slight bias
> > +					towards low power
> > +		balanced:		Balance between low power consumption
> > +					and performance
> > +		balanced-performance:	Balances between performance and low
> > +					power consumption with a slight bias
> > +					towards performance
> > +		performance:		Emphasises performance (and may lead to
> > +					higher temperatures and fan speeds)
> > +
> > +		Userspace may expect drivers to offer at least several of these
> > +		standard profile-names! If none of the above are a good match
> > +		for some of the drivers profiles, then drivers may use one of
> > +		these extra profile-names:
> > +		<reserved for future use>
> > +
> > +What:		/sys/class/performance_profile/<device>/current_profile
> > +Date:		October 2020
> > +Contact:	Hans de Goede <hdegoede@xxxxxxxxxx>
> > +Description:
> > +		Reading this file gives the current selected profile for this
> > +		device. Writing this file with one of the strings from
> > +		available_profiles changes the profile to the new value.
> > +
> > +		Reading this file may also return "custom". This is intended for
> > +		drivers which have and export multiple knobs influencing
> > +		performance. Such drivers may very well still want to offer a
> > +		set of profiles for easy of use and to be able to offer a
> > +		consistent standard API (this API) to userspace for configuring
> > +		their performance. The "custom" value is intended for when a
> > +		user has directly configured the knobs (through e.g. some
> > +		advanced control-panel for a GPU) and the knob values do not
> > +		match any of the presets represented by the
> > +		performance-profiles. In this case writing this file will
> > +		override the modifications and restore the selected presets.
> > +
> > +What:		/sys/class/performance_profile/<device>/type
> > +Date:		October 2020
> > +Contact:	Hans de Goede <hdegoede@xxxxxxxxxx>
> > +Description:
> > +		Performance-profiles may be system-wide, or for a specific
> > +		device (e.g. CPU / GPU). System-wide profiles are typically
> > +		used on devices where where a single cooling solution is
> > +		shared between all components, such as laptops and NUCs.
> > +
> > +		Reading this file indicates the type of the device for which
> > +		the thermal-profile is being configured.
> > +
> > +		Valid values: "system"
> > +		Reserved for future use values: "cpu", "gpu"