Re: [PATCH 5/5] hw/mem/cxl_type3: Refactor CDAT sub-table entry initialization into a function

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

On Thu, 13 Oct 2022 15:40:47 -0400
Gregory Price <gregory.price@memverge.com> wrote:

> > >      /* For now, no memory side cache, plausiblish numbers */
> > > -    *dslbis_nonvolatile1 = (CDATDslbis) {
> > > +    *dslbis1 = (CDATDslbis) {
> > >          .header = {
> > >              .type = CDAT_TYPE_DSLBIS,
> > > -            .length = sizeof(*dslbis_nonvolatile1),
> > > +            .length = sizeof(*dslbis1),
> > >          },
> > > -        .handle = nonvolatile_dsmad,
> > > +        .handle = dsmad_handle,
> > >          .flags = HMAT_LB_MEM_MEMORY,
> > >          .data_type = HMAT_LB_DATA_READ_LATENCY,
> > >          .entry_base_unit = 10000, /* 10ns base */
> > >          .entry[0] = 15, /* 150ns */  
> > 
> > If we are going to wrap this up for volatile / non-volatile 
> > we probably need to pass in a reasonable value for these.
> > Whilst not technically always true, to test the Linux handling
> > I'd want non-volatile to report as longer latency.
> >   
> 
> Here's a good question
> 
> Do we want the base unit and entry to be adjustable for volatile and
> nonvolatile regions for the purpose of testing?  Or should this simply
> be a static value for each?

We definitely want a 'default' value if nothing is provided.
It might be useful to allow it to be adjusted, but lets add that when
we have a use for it (perhaps testing some stuff in kernel where the
values matter enough to make them controllable).

> 
> Since we need to pass in (is_pmem/is_nonvolatile) or whatever into the
> cdat function, we could just use that to do one of a few options:
>     1) Select from a static value
>     2) Select a static value and apply a multiplier for nvmem
>     3) Use a base/value provided by the use and apply a multiplier
>     4) Make vmem and pmem have separately configurable latencies

For now 1 is fine I think.

I've just pushed out a doe-v9 tag and cxl-2022-10-14 branch to 
gitlab.com/jic23/qemu  Also advanced the base tree to current QEMU mainline.

Note that if anyone is playing with the switch cci device and mainline kernel
you'll currently need to revert
https://lore.kernel.org/linux-pci/20220905080232.36087-5-mika.westerberg@linux.intel.com/

Jonathan