34.8. KVM networking performance
By default, KVM virtual machines are assigned a virtual Realtek 8139 (rtl8139) NIC (network interface controller).
The rtl8139 virtualized NIC works fine in most environments. However, this device can suffer from performance degradation problems on some networks, for example, a 10 Gigabit Ethernet network.
To improve performance switch to the para-virtualized network driver.