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

> -----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(a)redhat.com; eblake(a)redhat.com; gaofeng(a)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.