Open Stack

The only reason I can think of is that they are doing nested VMs and don't
have the right nesting flag enabled in their base flag.

On Tue, May 3, 2016 at 9:01 AM, 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
> performance.
>
> 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 ?
>
> Regards,
> Daniel
> --
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