We have installed a Windows 2008R2 server onto a 2012 HyperV host however we only gave it 1 virtual CPU to access. Generally when I watch the two servers act/react as far as overall CPU usage is concerned they seem synchronous, the host appears to spread the guests work across 4 cores out of 8 available though the guest only sees one CPU.
My question is would adding a second vCPU via the HyperV console at host level reflect in the guest OS? Would the guest OS see more CPU instances? Become multi-threaded? Is adding more vCPUs to the guest OS going to add anything tangible to it?