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Re: [Qemu-devel] -cpu check, rdtscp and AMD KVM
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] -cpu check, rdtscp and AMD KVM |
Date: |
Thu, 12 Nov 2015 17:35:59 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 12/11/2015 17:27, Eduardo Habkost wrote:
>> > > To simply remove rdtscp from all Opteron_G* models?
> >
> > Not sure this is the right thing to do... Real hardware has it, and
> > going forward KVM will provide it.
>
> Do you see any alternative?
Live with the warning, and document it in the release notes.
> We need AMD CPU models that can run
> out of the box using today's kernels. As no existing VMs running
> Opteron_G* on AMD CPUs have rdtscp, I believe it makes sense to
> just define Opteron_G* without rdtscp.
>
> When we add SVM rdtscp support to KVM, we can add new
> "Opteron_G[2-5]-rdtscp" CPU models.
Makes sense too.
However, I'm a bit afraid of the interaction with libvirt. Right now,
libvirt has rdtscp in the description. If we remove it from libvirt,
libvirt will start adding +rdtscp to the QEMU CPU command line option,
so our change will be moot. And if we do not remove it from libvirt,
libvirt will not be able to start a VM with rdtscp on a fixed kernel.
Is this correct?
Paolo