What is the effect of doubling the number of available PCIe ports (-device pcie-root-port)?

[ILIV]

Hi! 

We've been trying to understand what the effect of increasing number of 
'-device pcie-root-port...' might be in terms of system resources consumption 
and overall system performance. 

In this specific scenario, we're running an oVirt deployment with about 100 
hosts and thousands of VMs.

oVirt allocates 16 PCIe ports by default (or is it QEMU defaults?) and we would 
like to increase that number to about 30. 

However, only very few VMs are actually gonna use those extra PCIe ports in 
terms of having additional devices (e.g. NICs). 

So, basically, there will be a lot of VMs that have about twice as many PCIe 
ports available to them than now but not really using them (as in having actual 
additional devices created and associated with the VMs). 

How does that change load/utilization of the physical servers that are running 
the VMs? Any potential problems for VMs themselves?

Ivan