faster: Xen or qemu+kvm?

Magnus Runesson mr-ubuntu at
Tue Jan 2 16:05:37 UTC 2007

On Tue, 2007-01-02 at 16:18 +0100, Felipe Alfaro Solana wrote:
> On 1/2/07, Mihamina Rakotomandimby

> Other full virtualization solutions (like QEMU, VMware, etc.) are
> inherently slower since the gues OS runs unmodified and it requires a
> lot of "magic" being done by the hypervisor to virtualize hardware and
> privileged access.

Note that QEMU and KVM+QEMU are not comparable in performance. KVM+QEMU
gives very close to native performance as you can get since it take
advantage of the hardware virtualization support in the CPU, like Xen
does. QEMU is instead as slow as VMWare.

Since neither Xen nor KVM are in Ubuntu yet. KVM is much easier to set
up than Xen. KVM just requires two new kernel modules, but Xen requires
a patched host kernel. Xen, on the other hand, have nice support for
representing hardware like TV-cards to the guests.

Due to get the best performance I think it is very important to use raw
devices instead of files as disks for the virtual machines. Of course,
as always enough with RAM.

At the moment my server is running Xen and para-virualized hosts and I
have KVM on my laptop to run test environments. All hosts are running


Magnus Runesson <mr-ubuntu at>

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