Re: [edk2-devel] [edk2-platforms] [PATCH v1 2/3] Platform/ARM/SgiPkg: Add HMAT ACPI table for RdN1EdgeX2

["Vijayenthiran Subramaniam" <vijayenthiran.subramaniam@arm.com>]

Hi Jonathan,

On Mon, Feb 1, 2021 at 11:16 AM Jonathan Cameron via groups.io
<jonathan.cameron=huawei.com@groups.io> wrote:
>
> On Fri, 29 Jan 2021 17:11:03 +0000
> Vijayenthiran Subramanian <vijayenthiran.subramaniam@arm.com> wrote:
>
> Hi Vijayenthiran,
>
> ....
>
> > > > > +  // Memory Proximity Domain
> > > > > +  {
> > > > > +    EFI_ACPI_6_3_HMAT_STRUCTURE_MEMORY_PROXIMITY_DOMAIN_ATTRIBUTES_INIT (
> > > > > +      1, 0x0, 0x0),
> > > > > +    EFI_ACPI_6_3_HMAT_STRUCTURE_MEMORY_PROXIMITY_DOMAIN_ATTRIBUTES_INIT (
> > > > > +      1, 0x1, 0x1),
> > > > > +   },
> > > > > +
> > > > > +  // Latency Info
> > > > > +  EFI_ACPI_6_3_HMAT_STRUCTURE_SYSTEM_LOCALITY_LATENCY_AND_BANDWIDTH_INFO_INIT (
> > > > > +    0, 0, INITATOR_PROXIMITY_DOMAIN_CNT, TARGET_PROXIMITY_DOMIAIN_CNT, 100),
> > > > > +  {
> > > > > +    {0, 1}, {0, 1},
> > > > > +    {
> > > > > +      10, 20,
> > > > > +      20, 10,
> > > > > +    }
> > > > > +  },
> > >
> > > Hi,
> > >
> > > Now either you have a very odd machine in which latencies are round numbers that happen
> > > to look like the values in SLIT or ... ?
> > >
> > > HMAT has very carefully defined real world units to overcome the fact that there
> > > was no standard scaling etc for SLIT.  It is not a good idea to put tables out
> > > there which don't do this right as someone may copy this for a real system
> > > and we end up with HMAT being roughly as useless for performance prediction as
> > > SLIT is.  That is not something I would want to see.
> > >
> > > Jonathan
> >
> > This patch is for a platform that is modelled and not for an actual board. So
> > the latencies are hypothetical but ensure that the typical latency between two
> > chips is represented. These tables are not expected to be copied for another
> > platform without understanding what these values mean. Such a copy, without
> > understanding what is being copied, would be an error in judgement on the part
> > of the person doing it. The commit message of this patch (in v2) can be updated
> > to exercise caution on reusing these values.
> >
> > [1]: https://developer.arm.com/products/system-design/fixed-virtual-platforms
>
> No one reads commit messages.  So if you want to avoid people copying them put a
> comment in the actual file.  Or just make up some more plausible numbers :)
> All we really need here is to avoid giving the impression that copying numbers from
> SLIT is valid.
>
> Jonathan
>

Sure, I will add a comment in the file as well.

Regards,
Vijayenthiran