Re: [RFC/RFT][PATCH 4/7] cpuidle: menu: Split idle duration prediction from state selection

[Peter Zijlstra]

On Sun, Mar 04, 2018 at 11:26:24PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> 
> In order to address the issue with short idle duration predictions
> by the idle governor after the tick has been stopped, prepare the
> menu governor code for reordering with respect to the timekeeping
> code that stops the tick.
> 
> Use the observation that menu_select() can be split into two
> functions, one predicting the idle duration and one selecting the
> idle state, and rework it accordingly.

I actually think this is the wrong way around.

We really should be predicting state not duration. Yes the duration
thing is an intermediate value, but I don't think it makes any sense
what so ever to preserve that in the predictor. The end result is the
idle state, we should aim for that.

As per:

  https://lkml.org/lkml/2017/7/18/615

there are definite advantages to _not_ preserving duration information
beyond the state boundaries.