[Engine-devel] CPU topology in the API

[Geert Jansen]

On 04/30/2012 02:43 PM, Dor Laor wrote:
>> I would go for 4 or 2
>> Current CPU topology for the hosts is a new commit, thus it may be
>> allowed to change it now since no one is using it yet. This works in
>> favour of 2. In any case only 3 discloses all the information in all
>> possible cases.
>>
>>
>> Thoughts?
>
> If you touch any of this, please be prepared for the future:
>   - Use hyperthreads (exists in kvm today)
>   - Add numa topology for guest and the hosts
>   - Add Cache info (for VMs too)
>   - Add number of DIMMs, especially for VMs, for the upcoming memory hot
>     plug feature.
>   - BE ready for cpu/cpu/memory hotplug for the hosts and the guests.

Maybe there will be a time where we need this, but for now we just need 
the total number of cores. This is important for capacity planning. For 
CPU, these capacity planning tools simply add up all the fractional core 
usages for all VMs in a cluster, and then it has to be smaller than the 
number of total cores in the cluster. So it's important to know the 
total number of cores per host.

For a VM, the number of cores is sockets*cores. For a host, it is just 
"cores". If you would use socket*cores for a host, you'll get too many. 
This isn't obvious and in my view it's a bug.

Simon, I don't really see this as an API breaker by the way. The number 
of cores for a host was always cores*sockets even on 3.0, just that 
sockets was always equal to 1 (implicitly).

Regards,
Geert