-----Original Message----- From: Daniel P. Berrange [mailto:berrange@redhat.com] Sent: Wednesday, November 14, 2012 6:45 PM To: Ichikawa, Ken/市川 顕 Cc: libvir-list@redhat.com; eblake@redhat.com; gaofeng@cn.fujitsu.com; Kaneshige, Kenji/金重 憲治 Subject: Re: [PATCH] qemu conf: Use host-model for cpu mode by default
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.
Ken's patch is not just to change the default cpu mode to host-model. Cpu mode is set to host-model only when user specifies "make_default_cpu_host_model = 1" in qemu.conf. So I don't think it cause the problem. Regards, Kenji Kaneshige
Daniel -- |: 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 :|