I have a dual Opteron server running Linux with libvirt to host several VMs. The VMs work fine and the server processes OK, but I notice one CPU always runs about 69C (throttles at 70C) and the other runs about 15C.

This doesn't seem normal to me? Shouldn't they both be a little closer in temperature?

I'm not sure how to dianose any further. Maybe there isn't enough thermal paste on one of the CPUs?

Edit: The motherboard is ASUS KGPE-D16 and cooled by dual Noctua NH-U9DO fans.

Note that I think the temperatures might be degress above ambient, rather than absolute values? When the server is idling, the CPU temperatures drop to 2C and 13C. I am using the lmsensors configuration from here