Re: [RFC PATCH] topology: Represent clusters of CPUs within a die.

[Brice Goglin]

Le 19/10/2020 à 16:16, Morten Rasmussen a écrit :
>
>>> If there is a provable benefit of having interconnect grouping
>>> information, I think it would be better represented by a distance matrix
>>> like we have for NUMA.
>> There have been some discussions in various forums about how to
>> describe the complexity of interconnects well enough to actually be
>> useful.  Those have mostly floundered on the immense complexity of
>> designing such a description in a fashion any normal software would actually
>> use.  +cc Jerome who raised some of this in the kernel a while back.
> I agree that representing interconnect details is hard. I had hoped that
> a distance matrix would be better than nothing and more generic than
> inserting extra group masks.
>

The distance matrix is indeed more precise, but would it scale to
tens/hundreds of core? When ACPI HMAT latency/bandwidth was added, there
were concerns that exposing the full matrix would be an issue for the
kernel (that's why only local latency/bandwidth is exposed n sysfs).
This was only for NUMA nodes/targets/initiators, you would have
significantly more cores than that.

Brice