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

[Rafael J. Wysocki]

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. :-)

Thanks!


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.