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

["Iyer, Sundar" <sundar.iyer@intel.com>]

> -----Original Message-----
> From: Morten Rasmussen [mailto:morten.rasmussen@arm.com]
> Sent: Monday, May 12, 2014 4:02 PM
>
> > And which is why I mentioned that this is heavily platform dependent.
> > This is completely dependent on how the rest of the system power
> management works.
> 
> Agree. Race to halt/idle is not universally a good idea. It depends of the
> platform energy efficiency at the higher performance states, idle power
> consumption, system topology, use-case, and anything else that consumes
> power while the tasks are running. For example, if your energy efficiency is
> really bad in the turbo states, it might be worth going a bit slower if the total
> energy can be reduced.

Apart from the specifics of the CPU/topology, race to halt doesn't contribute significant
to workloads which are offloaded/accelerated: e.g. video, media workloads.

That said, I think the energy conservation boils down to (not limited to):

a. should we schedule wide (multiple CPUs) vs local (fewer CPUs);
b. should we burst (higher P-states) vs run slow (lower P-states); 
c. is the control resource (power, clock etc.) shared wide or local to the unit;
d. Is the "local good" aka sub-system conservation resulting in "global good" aka
platform conservation?
e. what is the extent of options we want to load the user with: is the user going to toggle
some 200 switches to get the best experience or the user space/kernel will abstract a bulk
of these and provide more intelligent actions/decisions?

And I think the following should be the general outline of any efforts:

a. if the savings result in violation of any user defined quality-of-service for the experience (
finite FPS, finite computational requirements like encode/decode compute requirement etc.)
b. if we can conserve energy at the "platform" level vs "sub-system" level;
c. If we do save @ the "sub-system" level, how much of this is dependent on the specific
system architecture/topology/ vs "generic"; or in other words, how much of hit will a different
architecture suffer (?)

Cheers!