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

[Lukasz Luba]

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