[CentOS-virt] xen kernel showing only one processor on SMP

[gen2]

Hristo Benev wrote:
> What if you boot with other kernel?
> 
> If you have the same result maybe BIOS update is required for your server?!

Hi thanks for the response
BIOS is updated and current, if I boot to gentoo liveCD, I see the 
expected 4 processors. This server has indeed shown TWO processors using 
centOS xen-kernel before, but now after some time and upgrades I notice 
there is only one (again!).

Is it as simple as BIOS in every case, or is there some other path to 
discovering the problem I can try? (I have done many many hours of forum 
searches and googling on this issue) Thank you