On Mon, Mar 12, 2012 at 04:49:47PM +0100, Andreas Färber wrote: > Am 11.03.2012 17:16, schrieb Gleb Natapov: > > 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. > > This sounds pretty much like what Liu Jinsong and Jan are discussing in > the TSC thread on qemu-devel. (cc'ing) I'll look for that thread. Thanks! > > IMO interpreting an explicit -cpu parameter depending on -M would be > wrong. Changing the default CPU based on -M is fine with me. For an > explicit argument we would need Westmere-1.0 analog to pc-1.0. Then the > user gets what the user asks for, without unexpected magic. It is not unexpected magic. It would be a documented mechanism: "-cpu Nehalem-1.0" and "-cpu Nehalem-1.1" would have the same meaning every time, with any machine-type, but "-cpu Nehalem" would be an alias, whose meaning depends on the machine-type. Otherwise we would be stuck with a broken "Nehalem" model forever, and we don't want that. > Note that on my qom-cpu-wip branch [1] (that I hope to have cleaned up > and sent out by tomorrow), all built-in CPUs become statically > registered QOM types. The external definitions that get passed in via > -cpudef become dynamically registered QOM types; I took care to allow > overriding existing classes with the specified -cpudef fields (but > untested). Setting family, level, etc. for -cpu is done on the X86CPU > object instance. [2] > What I don't have yet are QOM properties to set the fields from, e.g., > machine code, but those should be fairly easy to add. Sounds interesting. I will have to take a look at the code to understand how it affects what's being discussed in this thread. > > Andreas > > [1] http://repo.or.cz/w/qemu/afaerber.git/shortlog/refs/heads/qom-cpu-wip > > [2] > http://repo.or.cz/w/qemu/afaerber.git/commit/8a6ede101a2722b790489989f21cad38d3e41fb5 > > -- > SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany > GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg -- Eduardo -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list