FlexVF: Adaptive network device services in a virtualized environment

Single-root I/O virtualization (SR-IOV) allows virtual machines direct access to physical network cards through so-called virtual functions (VFs), considerably reducing networking overhead compared to paravirtualized interfaces by avoiding the hypervisor’s network stack. However, the maximum number of VFs on each card is often limited compared to the number of VMs running on each host, leading to the problem of choosing which VMs to allocate these VFs. In this paper, we introduce FlexVF, a mechanism for dynamically allocating and switching between VFs and paravirtualized networking on VMs based on network activity monitoring. We show that FlexVF improves VM network performance by 75% without affecting network operation.