Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

Peter Zijlstra
2017-07-18T18:55:22Z

On Mon, Jul 17, 2017 at 12:48:38PM -0700, Arjan van de Ven wrote:
> On 7/17/2017 12:23 PM, Peter Zijlstra wrote:
> > Of course, this all assumes a Gaussian distribution to begin with, if we
> > get bimodal (or worse) distributions we can still get it wrong. To fix
> > that, we'd need to do something better than what we currently have.
> >
>
> fwiw some time ago I made a chart for predicted vs actual so you can sort
> of judge the distribution of things visually
>
> http://git.fenrus.org/tmp/linux2.png

That shows we get it wrong a lot of times (about 50%, as per the
average) and moving the line has benefit. Since for performance you
really don't want to pick the deeper idle state, so you want to bias
your pick towards a shallower state.

Using the CDF approach you can quantify by how much you want it moved.