[libvirt] [RFC] Data in the <topology> element in the capabilities XML

[Peter Krempa]

On 01/17/13 10:36, Daniel P. Berrange wrote:
>>
>> Well not for all machines in the wild out there. This is a very
>> similar approach that libvirt uses now to detect the topology and it
>> is not enough to detect threads on AMD Bulldozer as the cpus
>> corresponding to the threads have different core_id's (they are also
>> considered as cores from the perspective of the kernel). This is
>> unfortunate for the virtualization management tools as oVirt that
>> still consider the AMD Bulldozer "module" as a 1 core with two
>> threads, even if it registers as two cores.
>>
>> For AMD Bulldozer to be detected correctly, we would need to expose
>> the thread_id's along with thread siblings information to determine
>> the two threads belonging together.
>
> NB, the socket_id / core_id values in the above XML are *not* intended
> to be anyway related to similarly named values in /proc/cpuinfo. They
> are values libvirt assigns to show the topology accurately.

Hm, in that case I'm not sure if it's worth bothering with detecting the 
topology, then (possibly) making up the data provided in the XML. The 
management applications then will have to calculate the topology from 
our data again just to know the topology. For other possible uses of the 
data the management app would still need to re-detect it on their own if 
they need (for some reason) the actual data.

Also, even with non-real data in these fields here it won't enable us to 
reflect the topology of AMD Bulldozer reliably. We would have to choose 
whether we'd like to report the modules as cores or threads. And each of 
these choices will possibly make someone complain that they don't like 
the choice.

Peter
>
>
> Daniel
>