Re: [PATCH] Documentation: Add documentation for new platform_profile sysfs attribute

[Bastien Nocera]

Hey Hans, Mark,

On Tue, 2020-10-27 at 12:42 -0400, Mark Pearson wrote:
> From: Hans de Goede <hdegoede@xxxxxxxxxx>
> 
> 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 somei
> 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

Can you please make sure to quote 'platform-profile' and 'profile-name'
this way all through the document? They're not existing words, and
quoting them shows that they're attribute names, rather than English.

> consumption or towards performance (and higher power consumption and
> thermals).

s/thermal/temperature/

"A thermal" is something else (it's seasonal underwear for me ;)

> Introduce a new platform_profile sysfs API which offers a generic API
> for
> selecting the performance-profile of these automatic-mechanisms.
> 
> Co-developed-by: Mark Pearson <markpearson@xxxxxxxxxx>
> Signed-off-by: Mark Pearson <markpearson@xxxxxxxxxx>
> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> ---
> Changes in V1:
>  - Moved from RFC to proposed patch
>  - Added cool profile as requested
>  - removed extra-profiles as no longer relevant
> 
>  .../ABI/testing/sysfs-platform_profile        | 66
> +++++++++++++++++++
>  1 file changed, 66 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-platform_profile
> 
> diff --git a/Documentation/ABI/testing/sysfs-platform_profile
> b/Documentation/ABI/testing/sysfs-platform_profile
> new file mode 100644
> index 000000000000..240bd3d7532b
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-platform_profile
> @@ -0,0 +1,66 @@
> +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
> +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).
> +
> +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 are a rather meaningless way to describe platform-
> profiles

It's not meaningless, but rather ambiguous. For a range of 1 to 5, is 1
high performance, and 5 low power, or vice-versa?

> +this API uses strings to describe the various profiles. To make sure
> that
> +userspace gets a consistent experience when using this API this API

you can remove "when using 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.

"for some reason" can be removed.

>  Drivers which wish to introduce new profile-names must:
> +1. Have very good reasons to do so.

"1. Explain why the existing 'profile-names' cannot be used"

> +2. Add the new profile-name to this document, so that future drivers
> which also
> +   have a similar problem can use the same name.

"2. Add the new 'profile-name' to the documentation so that other
drivers can use it, as well as user-space knowing clearly what
behaviour the 'profile-name' corresponds to"

> +
> +What:          /sys/firmware/acpi/platform_profile_choices
> +Date:          October 2020
> +Contact:       Hans de Goede <hdegoede@xxxxxxxxxx>
> +Description:
> +               Reading this file gives a space separated list of
> profiles
> +               supported for this device.

"This file contains a space-separated list of profiles..."

> +
> +               Drivers must use the following standard profile-
> names:
> +
> +               low-power:              Emphasises low power
> consumption
> +               cool:                   Emphasises cooler operation
> +               quiet:                  Emphasises quieter operation
> +               balanced:               Balance between low power
> consumption
> +                                       and performance
> +               performance:            Emphasises performance (and
> may lead to
> +                                       higher temperatures and fan
> speeds)

I'd replace "Emphasises" with either "Focus on" or the US English
spelling of "Emphasizes".

> +               Userspace may expect drivers to offer at least
> several of these
> +               standard profile-names.

Replce "at least several" with "more than one".

> +
> +What:          /sys/firmware/acpi/platform_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.

Is there another file which explains whether those sysfs value will
contain a trailing linefeed?

Cheers