Re: [PATCH 07/26] cxl/port: Add dynamic capacity size support to endpoint decoders

Ira Weiny
2024-05-06T04:07:50Z

Dan Williams wrote:
> Ira Weiny wrote:
> > > > else
> > > > free_pmem_start = cxlds->pmem_res.start;
> > > >
> > > > + /*
> > > > + * Limit each decoder to a single DC region to map memory with
> > > > + * different DSMAS entry.
> >
> > This prevents more than 1 region per DC partition (region).
>
> Why? Multiple regions per partition is the current status quo for other
> partition types.
>
> > > I notice in the pmem equivalent there is a case for part of the region already mapped.
> > > Can that not happen for a DC region as well?
> >
> > See above check. Each DC region (partition) was to be associated with a
> > single DSMAS entry. I'm unclear now why that decision was made.
>
> The limitation of one DSMAS per partition makes sense otherwise that
> would indicate performance across different spans of the partition.
>
> > It does not seem hard to add this though. Do we really need that ability
> > considering dax devices are likely going to be the main boundry for users
> > of a DC region?
>
> It seems like extra work to make DCD a special case compared to the
> other partition types, so the burden of proof is the other way. Why
> tolerate DCD divergence from the status quo?

I don't remember the details. But this was discussed before in a call. I'm ok
adding this support. I have a test for it now. Just need to tweek a couple of
things.

Ira