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

[Hans de Goede <hdegoede@redhat.com>]

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@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.

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@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"