[libvirt] [PATCH] qemu conf: Use host-model for cpu mode by default

Ichikawa, Ken ichikawa.ken at jp.fujitsu.com
Thu Nov 15 02:38:12 UTC 2012

(2012/11/14 18:44:44), Daniel P. Berrange wrote:
> On Wed, Nov 14, 2012 at 03:10:48AM +0000, Ichikawa, Ken wrote:
> > Now, qemu guest's default cpu model is qemu32/64 and it can be 
> > configured per domain. In some case, host-model mode is suitable for 
> > getting enough performance in the guest because of features from cpu 
> > spec.
> >
> > This patch adds a config option to qemu.conf to use 'host-model' 
> > mode as default and allow users to use host-model mode in domains on a host.
> > This is useful because
> >  - Guest owners don't need to touch their domain's config.
> >  - An administrator can reduce an item in their checklist for VM
> >    performance and guarantee all guests should run in the best
> performance.
> While I understand the benefits, I'm afraid I have to NACK this at 
> this time because using host-model doesn't really work when trying to 
> use nested-KVM. Until we have a solution for that, we neeed to stick 
> with a CPU model that works everywhere, since users like OpenStack do 
> actually use nested-KVM for testing work and already complained about 
> this when I made OpenStack set the host-model by default.

Thank you for noticing the nested-KVM problem.
However, to enable this patch's function, users need to edit qemu.conf.
So, if users use nested-KVM, they just don't edit the conf file.
Is there still any problem?


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