How much of a performance does using QEMU virtualization incur on a Windows host, when both the host and vm are running the same CPU? Older articles indicate that using kqemu avoided the slow down in performance if both host and vm used the same instruction set. But it seems that kqemu is not used much recently or is not available for 64 bit systems.

Are more recent versions capable of maintaining performance without the use of `kqemu'?

  • kqemu is long since deprecated. have you checked kvm?
    – dyasny
    May 20, 2015 at 2:31

1 Answer 1


On a Windows host, qemu isn't actually a hypervisor, but is doing full machine emulation with dynamic translation, which is horrendously slow, and there's little that can be done to speed it up.

It's maybe useful as a demonstration or for debugging purposes, but for anything serious you will want to use an actual Windows hypervisor such as Hyper-V, or some other actual hypervisor entirely (e.g. KVM on Linux).

  • If the CPU qemu is emulating is the same as the host CPU doesn't qemu run some of the commands directly without translating them? Do new versions of qemu have some of the kqemu options directly built-n?
    – vfclists
    May 20, 2015 at 10:08
  • @vfclists I suppose it could be made to do, but this is such an unusual (and not commonly desired) case that there's no reason to put much effort into it. May 20, 2015 at 21:22
  • I guess I haven't really grasped the difference between emulation and virtualization as it seems that QEMU was designed to emulate rather than virtualize. I suppose that the purpose of kqemu was not necessarily to make QEMU a better emulator or virtualizer, only to speed it up.
    – vfclists
    May 20, 2015 at 21:37

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