To overcome this, modern processors support virtualization extensions, such as Intel VT-x and AMD-V. As you can imagine this has a massive performance impact.

But what is full virtualization, you may ask? When a CPU is emulated (vCPU) by the hypervisor, the hypervisor has to translate the instructions meant for the vCPU to the physical CPU. It is a type 1 hypervisor that is a full virtualization solution for Linux on x86 hardware containing virtualization extensions (Intel VT or AMD-V). Though QEMU can run on its own and emulate all of the virtual machine’s resources, as all the emulation is performed in software it is extremely slow. It is flexible in that it can emulate CPUs via dynamic binary translation (DBT) allowing code written for a given processor to be executed on another (i.e ARM on x86, or PPC on ARM). QEMU is a userland type 2 (i.e runs upon a host OS) hypervisor for performing hardware virtualization (not to be confused with hardware-assisted virtualization), such as disk, network, VGA, PCI, USB, serial/parallel ports, etc. I mean, are they the same, or are they different? Aren't they both hypervisors? Let’s dive in. The differences between QEMU and KVM are not always clear. Whether you are running VNF’s in OpenStack or deploying virtual environments within GNS3 or EVE-NG, it is important to understand the different virtualization technologies, such as QEMU and KVM, even for us network engineers.

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