Re: [External] Re: RFC: offering a standardized (/sys/class) userspace API for selecting system/laptop performance-profiles

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

Hi Mark,

On 9/17/20 6:58 PM, Mark Pearson wrote:
> On 9/17/2020 10:10 AM, Benjamin Berg wrote:
>> Hi,
>>
>> On Thu, 2020-09-17 at 15:54 +0200, Hans de Goede wrote:
>>> Hi,
>>>
>>> On 9/17/20 3:50 PM, Benjamin Berg wrote:
>>>> On Thu, 2020-09-17 at 14:51 +0200, Hans de Goede wrote:
>>>>>> Compared to the WIP lenovo-dytc "perfmode" driver, we're missing
>>>>>> something to advertise the unavailability of a profile, and the reason
>>>>>> for that unavailability.
>>>>>
>>>>> UGh, do we really need to export this though. We have the lap_mode thing
>>>>> already; and that is something which we will need for other reasons in
>>>>> the future too. Any UI for selecting performance modes can display a
>>>>> warning when lap_mode is true saying that: "The laptop has detected that it
>>>>> is sitting on someone's lap and that performance may be limited
>>>>> because of this." (feel free to improve the text).
>>>>
>>>> Well, for dytc_perfmode there are actually always the three states
>>>> L/M/H. It just happens that the kernel will write "H*" (was "M*" until
>>>> yesterday) when the performance mode is degraded due to lap detection.
>>>>
>>>> Think of dytc_perfmode as a profile that sets a number of things:
>>>>    * Thermal Limits
>>>>    * Fan Behaviour
>>>>    * possibly more
>>>>
>>>> While dytc_lapmode will only enforce a change to the thermal limit.
>>>> So "performance" (H) is technically a valid mode even when the lap is
>>>> detected.
>>>>
>>>>> I guess we could split the "value" attribute from my reply to Benjamin's
>>>>> email into "configured_value" (rw) and "actual_value" (rw) attributes.
>>>>> If we have the info we might as well export it I guess,.
>>>>
>>>> I consider the "*" purely a curtsey to users that read the attribute
>>>> directly using e.g. cat to help with the interpretation. It probably is
>>>> not interesting to userspace applications/daemons.
>>>
>>> So if there is a difference between M and H and H* then I think we should
>>> just do the KISS thing and only have a single value attribute and in the
>>> new interface handle the H* like H (p-p-d can still check the lap_mode
>>> attribute to differentiate the 2 if it wants to).
>>
>> I guess you are saying to drop "H*" and only have "L"/"M"/"H"? If so,
>> fine with me, but we probably need that input in reply to
>>    https://patchwork.kernel.org/patch/11730133/#23618881
>> then :)
>>
>> In principle it could be useful for userspace to know that performance
>> is or would be dramatically impacted. i.e. when dytc_lapmode is 1, then
>> you might want to say something like:
>>
>>    performance states >= 75 are impacted due to "lapmode"
>>
>> But, not sure if a kernel interface for that is useful or whether we
>> should just put that kind of knowledge into userspace.
>>
>> Benjamin
>>
> I don't have a strong opinion on this but the kernel driver is already knowledgeable about the quirks of what does and doesn't work on the system so it seems like a good place to have that logic.
> 
> What if we have an API for "configured" and "actual" - and if they differ userspace knows it should figure out why (likely lapmode, but if the HW vendor adds a new setting related to "position of sun in the sky" or "how much money is in your account and can you afford the electricity bill?" that could be added too....)

As I understand the problem with the configured and actual value/performance_level ideas is that if I understand things correctly that H* is not the same as M,
it behaves close-ish to M because of the lower thermal-limits from lapmode, but if I understood Benjamin correctly is is not exactly the same, so if we were
to advertise "M" in the actual_performance_level sysfs-attribute then that would not really be correct ?

Regards,

Hans