[Openstack-operators] User Survey usage of QEMU (as opposed to KVM) ?
Sergio Cuellar Valdes
scuellarv at kionetworks.com
Tue May 3 19:27:00 UTC 2016
On 3 May 2016 at 10:01, Daniel P. Berrange <berrange at redhat.com> wrote:
> Hello Operators,
> One of the things that constantly puzzles me when reading the user
> survey results wrt hypervisor is the high number of respondants
> claiming to be using QEMU (as distinct from KVM).
> As a reminder, in Nova saying virt_type=qemu causes Nova to use
> plain QEMU with pure CPU emulation which is many many times slower
> to than native CPU performance, while virt_type=kvm causes Nova to
> use QEMU with KVM hardware CPU acceleration which is close to native
> IOW, virt_type=qemu is not something you'd ever really want to use
> unless you had no other options due to the terrible performance it
> would show. The only reasons to use QEMU are if you need non-native
> architecture support (ie running arm/ppc on x86_64 host), or if you
> can't do KVM due to hardware restrictions (ie ancient hardware, or
> running compute hosts inside virtual machines)
> Despite this, in the 2016 survey 10% claimed to be using QEMU in
> production & 3% in PoC and dev, in 2014 it was even higher at 15%
> in prod & 12% in PoC and 28% in dev.
> Personally my gut feeling says that QEMU usage ought to be in very
> low single figures, so I'm curious as to the apparent anomoly.
> I can think of a few reasons
> 1. Respondants are confused as to the difference between QEMU
> and KVM, so are saying QEMU, despite fact they are using KVM.
> 2. Respondants are confused as to the difference between QEMU
> and KVM, so have mistakenly configured their nova hosts to
> use QEMU instead of KVM and suffering poor performance without
> realizing their mistake.
> 3. There are more people than I expect who are running their
> cloud compute hosts inside virtual machines, and thus are
> unable to use KVM.
> 4. There are more people than I expect who are providing cloud
> hosting for non-native architectures. eg ability to run an
> arm7/ppc guest image on an x86_64 host and so genuinely must
> use QEMU
> If items 1 / 2 are the cause, then by implication the user survey
> is likely under-reporting the (already huge) scale of the KVM usage.
> I can see 3. being a likely explanation for high usage of QEMU in a
> dev or PoC scenario, but it feels unlikely for a production deployment.
> While 4 is technically possible, Nova doesn't really do a very good
> job at mixed guest arch hosting - I'm pretty sure there are broken
> pieces waiting to bite people who try it.
> Does anyone have any thoughts on this topic ?
> Indeed, is there anyone here who genuinely use virt_type=qemu in a
> production deployment of OpenStack who might have other reasons that
> I've missed ?
> |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/
> |: http://libvirt.org -o- http://virt-manager.org
> |: http://autobuild.org -o- http://search.cpan.org/~danberr/
> |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc
> OpenStack-operators mailing list
> OpenStack-operators at lists.openstack.org
I'm confused too about the use of KVM or QEMU In the computes the
The output of:
nova hypervisor-show <id> | grep hypervisor_type
hypervisor_type | QEMU
The virsh dumpxml of the instances shows:
<domain type='kvm' id='44'>
But according to this document , it is using QEMU emulator instead of
KVM, because it is not using /usr/bin/qemu-kvm
So I really don't know if it's using KVM or QEMU.
* Sergio Cuéllar │DevOps Engineer*
Mexico City Phone (52) 55 8503 2600 ext. 4335
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