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SubjectRe: [RFC] Documentation: Add documentation for new performance_profile sysfs class
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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@lenovo.com>
> Cc: Elia Devito <eliadevito@gmail.com>
> Cc: Bastien Nocera <hadess@hadess.net>
> Cc: Benjamin Berg <bberg@redhat.com>
> Cc: linux-pm@vger.kernel.org
> Cc: linux-acpi@vger.kernel.org
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
> .../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.

> + 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@redhat.com>
> +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@redhat.com>
> +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@redhat.com>
> +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"
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