Re: [PATCH 1/3] sched/fair: Prepare variables for increased precision of EAS estimated energy

[Vincent Guittot]

On Wed, 7 Jul 2021 at 13:02, Lukasz Luba <lukasz.luba@xxxxxxx> wrote:
>
>
>
> On 7/7/21 11:50 AM, Vincent Guittot wrote:
> > On Wed, 7 Jul 2021 at 12:41, Lukasz Luba <lukasz.luba@xxxxxxx> wrote:
> >>
> >>
> >>
> >> On 7/7/21 11:32 AM, Vincent Guittot wrote:
> >>> On Wed, 7 Jul 2021 at 12:29, Lukasz Luba <lukasz.luba@xxxxxxx> wrote:
> >>>>
> >>>>
> >>>>
> >>>> On 7/7/21 11:11 AM, Vincent Guittot wrote:
> >>>>> On Wed, 7 Jul 2021 at 12:06, Lukasz Luba <lukasz.luba@xxxxxxx> wrote:
> >>>>>>
> >>>>
> >>>> [snip]
> >>>>
> >>>>>> No. It's in 0.1uW scale, so 800Watts. Which is 16 CPUs * 64Watts
> >>>>>
> >>>>> Oh! you want 0.1uW precision .... This doesn't seem realistic at all.
> >>>>> I'm not even sure that the power model can even reach an accuracy of
> >>>>> 1mW
> >>>>>
> >>>>
> >>>> True, the EM is registering platform with 1mW precision, but 1uW
> >>>
> >>> Do you mean 1uW or 0.1uW ?
> >>
> >> In this patch set I've proposed 0.1uW, but I'm open to drop one
> >> order of magnitude. The 1uW still be good.
> >
> > I don't want to underestimate the capabilities of the power model but
> > I don't see which benefit you will get with 0.1uW precision
> > With a 1uW precision the long type currently used for the returned
> > value is fine for 32bits machine AFAICT
> >
>
> For 1uW and 1.2Watts for one core, 4 CPUs in cluster we get:
> (1200 * 1000) * (4 * 1024) = ~4.9bln
> so it would need div 64 version

But as stated before, this is an internal computation step and doesn't
have to be reflected in the returned value which can stay a long