Re: [PATCH 1/8] Documentation, x86: Documentation for Intel Mem b/w allocation user interface

[Shivappa Vikas]

On Wed, 18 Jan 2017, Thomas Gleixner wrote:

> On Tue, 17 Jan 2017, Shivappa Vikas wrote:
> > On Mon, 16 Jan 2017, Thomas Gleixner wrote:
> > > This interface is really crap. The natural way to express it is:
> > >
> > >     Requested Bandwidth = X %
> >
> > I wanted to do it this way which did seem more intuitive but the issue is with
> > the non-linear scale which the hardware does not guarantee a particular
> > percentage for a particular value. Or we don't know the curve for delay value
> > vs. actual b/w throttled.
> >
> > ex: in non linear scale , the granularity is 2^n.
> > Max : 512
> >
> > Say a value of 256 is not guaranteed to have 50% or even follow a curve where
> > we can calculate the corresponding percentage.
>
> The question is whether this non linear scale thing is just a first
> implementation attempt and any sane hardware in the future will use the
> percentage value (which is an approximation as well).
>
> If that non-linear scale is not going to be prevalent, then we really can
> live with the fallout of a particular CPU type.
>
> If it's going to stay, then Intel should be able to provide simple tables
> which give us the required information for a particular CPU model.

By sample table - does this mean we can map a throttle value in non-linear 
scale to its percentage ?

Thanks,
Vikas

> Thanks,
>
> 	tglx