Re: [PATCH v3 2/2] cxl: Calculate region bandwidth of targets with shared upstream link

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Fri, 7 Jun 2024 09:12:31 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> On 6/7/24 7:30 AM, Jonathan Cameron wrote:
> >   
> >>>> +		if (is_cxl_root(parent_port)) {
> >>>> +			ctx->port = parent_port;
> >>>> +			cxl_coordinates_combine(ctx->coord, ctx->coord,
> >>>> +						dport->coord);    
> >>>
> >>> I'm a bit lost in all the levels of iteration so may have missed it.
> >>>
> >>> Do we assume that GP BW (which is the root bridge) is shared across multiple root
> >>> ports on that host bridge if they are both part of the interleave set?    
> >>
> >> Do we need to count the number of RPs under a HB and do min(aggregated_RPs_BW, (GP_BW / no of RPs) * affiliated_RPs_in_region)?  
> > 
> > I'm not 100% sure I understand the question.
> > 
> > Taking this again and expanding it another level.
> > 
> > 
> > 
> >       Host CPU
> > ______________________________________
> >         |                           |
> >         |                           |
> >         | 3 from GP/HMAT            | 3 from GP/HMAT
> >    _____|_____               _______|______
> >   RP         RP             RP            RP
> >   2|          |2           2|             |2
> >  __|__     ___|__         __|___        __|____
> > |1    |1  1|     |1      |1     |1     |1      |1
> > EP   EP    EP    EP     EP     EP      EP     EP
> > 
> > Then your maths
> > 
> > aggregated RPs BW is 8
> > (GP_BW/no of RPS) * affliated RPS in region.
> > = (3/2 * 4)
> > = 6  
> 
> While the result is the same, the math would be this below right?
> min((3/2 * 2), 4) + min((3/2 * 2), 4)

That's better, but I thought your thing above was about RPs in a HB vs
RPs across the whole thing.  Hence was trying to align with that.

I'm lost and it's end of Friday.  Lets work this out with code.

Jonathan
> 
> > Which is correct. So yes, I think that works if we assume everything is balanced.
> > I'm fine with that assumption as that should be the common case.
> > 
> > 
> > Jonathan
> > 
> >   
>