kvm steal time handling

[dubi]

Hi

I am currenlty having :
At the host : kernel 3.2.0-20-generic (original)
At the guest kernel 3.0.0-17-virtual (original)

With this combination steal time option was not active

In .config I set CONFIG_PARAVIRT_GUEST=y,CONFIG_PARAVIRT_TIME_ACCOU NTING=y
to enable steal time handling when the kernel is rebuild

Questions:
-Is it enough to use the newly build kernel as the host kernel (hypervisor) or also necessary to use it at all the guests of that hosts
-Does monitoring of steal time degrade guest performance a lot ?

thanks