Il 26/08/2014 20:01, Eduardo Habkost ha scritto: > On Tue, Aug 26, 2014 at 02:56:21PM +0200, Paolo Bonzini wrote: >> Il 25/08/2014 22:45, Eduardo Habkost ha scritto: >>> >>> TCG users expect the default CPU model to contain most TCG-supported features >>> (and it makes sense). See, for example, commit >>> f1e00a9cf326acc1f2386a72525af8859852e1df. >> >> It doesn't though (SMAP is the most egregious omission, and probably the >> main reason why people use QEMU TCG these days), and it raises the >> question of backwards-compatibility of qemu64---should we disable TCG >> features in old machine types? Probably yes, but we've never done that. > > Had we changed qemu64, any changes to the feature set of qemu64 would > probably require compatibility code on old machine-types for KVM, > anyway. But the last time qemu64 was changed was in 2009 (commit > f1e00a9cf326acc1f2386a72525af8859852e1df), it looks like everybody was > afraid of touching "qemu64" because its purpose was not very clear. > > 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? 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. Paolo -- 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
