On Wed, Aug 27, 2014 at 04:33:54PM +0200, Paolo Bonzini wrote: > Il 27/08/2014 16:05, Eduardo Habkost ha scritto: > > On Wed, Aug 27, 2014 at 03:36:51PM +0200, Paolo Bonzini wrote: > >> Il 26/08/2014 20:01, Eduardo Habkost ha scritto: > >>> So maybe that's good news, as things can be simpler if we make both TCG > >>> and KVM have similar behavior: > >>> > >>> * qemu64: a conservative default that should work out of the box on > >>> most systems, for both TCG and KVM. That's already the current status, > >>> we just need to document it. > >>> > >>> * -cpu host: for people who want every possible feature to be enabled > >>> (but without cross-version live-migration support). We can easily add > >>> support for "-cpu host" to TCG, too. > >> > >> This means that "-cpu host" has different meanings in KVM and TCG. Is > >> that an advantage or a disadvantage? > > > > It is the same meaning to me: "enable everything that's possible, > > considering what's provided by the underlying accelerator". The "host" > > name is misleading, though, because on KVM it is close to the host CPU, > > but on TCG it depends solely on TCG's capabilities. > > True. It's not very intuitive, but it is the same concept for processor > capabilities. > > Though for some leaves that do not correspond to processor capabilities, > "-cpu host" does set them to the host values. This is not just the > cache model, but also the family/model/stepping/vendor. > > For the TCG case, when running on a Nehalem it would be weird to see a > Nehalem guest with SMAP or ADOX support... I'm not sure it would even > work to have SVM with an Intel vendor. :) In that case, the best family/model/stepping/vendor choice depends on TCG capabilities (defined at compile time), not on the host CPU. ...and that proves your point: if we aren't even using the host CPU family/model/stepping, calling it "-cpu host" doesn't make much sense. If it is so different from the host model, we can call it "qemu64" (and do as you suggests below). > > >> If I have to choose blindly, I'd rather give different (but sane) > >> meanings to "-cpu qemu64" and the same meanings to "-cpu host"... > >> Basically "-cpu qemu32/64" on KVM would be changed automatically to > >> kvm32/64. > > > > This (different meanings to qemu64) is what I was proposing first, > > Good. > > > except for the "same meaning to -cpu host" part. What exactly would you > > expect "-cpu host" to mean on TCG? > > Emulate (as much as possible of) a SandyBridge if I'm running on a > SandyBridge, etc. > > "-cpu qemu64" would be the best CPU that TCG can do, with a standard > family/model/stepping/vendor slapped on top. Makes sense to me. -- Eduardo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
