Re: [libvirt] [Qemu-devel] Modern CPU models cannot be used with libvirt

On 03/11/2012 11:16 AM, Gleb Natapov wrote: >On Sun, Mar 11, 2012 at 10:33:15AM -0500, Anthony Liguori wrote: >>On 03/11/2012 09:56 AM, Gleb Natapov wrote: >>>On Sun, Mar 11, 2012 at 09:12:58AM -0500, Anthony Liguori wrote: >>>>-cpu best wouldn't solve this. You need a read/write configuration >>>>file where QEMU probes the available CPU and records it to be used >>>>for the lifetime of the VM. >>>That what I thought too, but this shouldn't be the case (Avi's idea). >>>We need two things: 1) CPU model config should be per machine type. >>>2) QEMU should refuse to start if it cannot create cpu exactly as >>>specified by model config. >> >>This would either mean: >> >>A. pc-1.1 uses -cpu best with a fixed mask for 1.1 >> >>B. pc-1.1 hardcodes Westmere or some other family >> >This would mean neither A nor B. May be it wasn't clear but I didn't talk >about -cpu best above. I am talking about any CPU model with fixed meaning >(not host or best which are host cpu dependant). Lets take Nehalem for >example (just to move from Westmere :)). Currently it has level=2. Eduardo >wants to fix it to be 11, but old guests, installed with -cpu Nehalem, >should see the same CPU exactly. How do you do it? Have different >Nehalem definition for pc-1.0 (which level=2) and pc-1.1 (with level=11). >Lets get back to Westmere. It actually has level=11, but that's only >expose another problem. Kernel 3.3 and qemu-1.1 combo will support >architectural PMU which is exposed in cpuid leaf 10. We do not want >guests installed with -cpu Westmere and qemu-1.0 to see architectural >PMU after upgrade. How do you do it? Have different Westmere definitions >for pc-1.0 (does not report PMU) and pc-1.1 (reports PMU). What happens >if you'll try to run qemu-1.1 -cpu Westmere on Kernel< 3.3 (without >PMU support)? Qemu will fail to start. So, you're essentially proposing that -cpu Westmere becomes a machine option and that we let the machines interpret it as they see fit? So --machine pc-1.0,cpu=Westmere would result in something different than --machine pc-1.1,cpu=Westmere?

That's something pretty different than what we're doing today. I think that we would have a single CPUX86 object and that part of the pc initialization process was to create an appropriately configured CPUx86 object.