libvirt users - Nov 2018 - performance overhead with backing chains?

Hi,

I was wondering if there are any studies on the performance overhead of a
QEMU/KVM virtual machine when the backing chain of its disk(s) is of size
n, with n > 1. In particular, it would be useful to know until what size we
can expect little or no impact on a Linux virtual machine, for instance.

Thanks!

Regards,
Riccardo