Re: [Ksummit-discuss] [TECH(CORE?) TOPIC] Energy conservation bias interfaces

[Daniel Lezcano <daniel.lezcano@linaro.org>]

On 05/14/2014 01:41 AM, Rafael J. Wysocki wrote:
> On Monday, May 12, 2014 10:43:22 PM Preeti U Murthy wrote:
>> On 05/12/2014 04:44 PM, Morten Rasmussen wrote:
>>> On Thu, May 08, 2014 at 09:59:39AM +0100, Preeti U Murthy wrote:
>>>> On 05/07/2014 10:50 AM, Iyer, Sundar wrote:
>
> [cut]
>
>>> While I agree that there are mechanisms to deal with thermal throttling
>>> already, I think it is somewhat related to energy-awareness. If you need
>>> throttling due to thermal constraints you are burning too much power in
>>> your system. If you factor in energy-effiency and the requirements for
>>> the current use-case you might be able to stay within the power budget
>>> with a smaller performance impact than blindly throttling all
>>> subsystems.
>>
>> True. I was intending to distinguish the who and the why in the above
>> two situations. My only point was that thermal throttling is undertaken
>> by platform and is a safety mechanism whereas switching to energy saving
>> mode when battery is low is undertaken by the kernel and will lead to
>> better end-user experience i.e.battery longevity. Yes the kernel is
>> expected to prevent the system from being throttled as much as possible.
>
> The kernel may very well be responsible for thermal throttling in some cases.
> At least it needs to be able to respond to "do not draw more power than this"
> type of requests.
>
> [cut]
>
>>>
>>> IIUC, you are proposing to have profiles setting a lot of kernel
>>> tunables rather than a single knob to control energy-awareness?
>>>
>>> My concern with profiles is that it basically exports most of the
>>> energy-awareness decision problems to user-space. Maybe I'm missing
>>> something? IMHO, it would be better to have more accurate energy related
>>> topology information in the kernel so it would be able to take the
>>> decisions.
>>
>> You are right. We shouldn't be exposing so many knobs to user-space and
>> expect the kernel to make good decisions based on these knobs being
>> tweaked by user space. How about a high level classification of profiles
>> like balanced, performance, powersave? These alone can be chosen by the
>> user and the lower end tunings left to the discretion of the kernel.
>
> Well, so we're actually back to a central knob with three levels effectively. :-)

May be we can consider adding the large number of knobs with debugfs ?


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