Commit 8e0cbf35 authored by Mark Pearson's avatar Mark Pearson Committed by Rafael J. Wysocki
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Documentation: Add documentation for new platform_profile sysfs attribute 



On modern systems the platform performance, temperature, fan and other
hardware related characteristics are often dynamically configurable. The
profile is often automatically adjusted to the load by some
automatic-mechanism (which may very well live outside the kernel).

These auto platform-adjustment mechanisms often can be configured with
one of several 'platform-profiles', with either a bias towards low-power
consumption or towards performance (and higher power consumption and
thermals).

Introduce a new platform_profile sysfs API which offers a generic API for
selecting the performance-profile of these automatic-mechanisms.

Co-developed-by: default avatarHans de Goede <hdegoede@redhat.com>
Signed-off-by: default avatarMark Pearson <markpearson@lenovo.com>
Signed-off-by: default avatarHans de Goede <hdegoede@redhat.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 5c8fe583

Documentation/ABI/testing/sysfs-platform_profile

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What:		/sys/firmware/acpi/platform_profile_choices

Date:		October 2020

Contact:	Hans de Goede <hdegoede@redhat.com>

Description:	This file contains a space-separated list of profiles supported for this device.



		Drivers must use the following standard profile-names:



		============	============================================

		low-power	Low power consumption

		cool		Cooler operation

		quiet		Quieter operation

		balanced	Balance between low power consumption and performance

		performance	High performance operation

		============	============================================



		Userspace may expect drivers to offer more than one of these

		standard profile names.



What:		/sys/firmware/acpi/platform_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

		platform_profile_choices changes the profile to the new value.

Documentation/userspace-api/index.rst

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@@ -24,6 +24,7 @@ place where this information is gathered. 
   ioctl/index

   iommu

   media/index

   sysfs-platform_profile



.. only::  subproject and html

Documentation/userspace-api/sysfs-platform_profile.rst

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=====================================================================

Platform Profile Selection (e.g. /sys/firmware/acpi/platform_profile)

=====================================================================



On modern systems the platform performance, temperature, fan and other

hardware related characteristics are often dynamically configurable. The

platform configuration is often automatically adjusted to the current

conditions by some automatic mechanism (which may very well live outside

the kernel).



These auto platform adjustment mechanisms often can be configured with

one of several platform profiles, with either a bias towards low power

operation or towards performance.



The purpose of the platform_profile attribute is to offer a generic sysfs

API for selecting the platform profile of these automatic mechanisms.



Note that this API is only for selecting the platform 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 on their own cannot represent the multiple variables that a

profile will adjust (power consumption, heat generation, etc) this API

uses strings to describe the various profiles. To make sure that userspace

gets a consistent experience the sysfs-platform_profile ABI document defines

a fixed set of profile names. Drivers *must* map their internal profile

representation onto this fixed set.



If 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. Explain why the existing profile names canot be used.

 2. Add the new profile name, along with a clear description of the

    expected behaviour, to the sysfs-platform_profile ABI documentation.