Il 23/07/2013 17:40, Eduardo Habkost ha scritto: > On Tue, Jul 23, 2013 at 05:09:02PM +0200, Paolo Bonzini wrote: >> Il 23/07/2013 16:13, Eduardo Habkost ha scritto: >>> On Tue, Jul 23, 2013 at 11:18:03AM +0200, Paolo Bonzini wrote: >>>> Il 22/07/2013 21:25, Eduardo Habkost ha scritto: >>>>> Bug description: QEMU currently gets all bits from GET_SUPPORTED_CPUID >>>>> for CPUID leaf 0xA and passes them directly to the guest. This makes >>>>> the guest ABI depend on host kernel and host CPU capabilities, and >>>>> breaks live migration if we migrate between host with different >>>>> capabilities (e.g. different number of PMU counters). >>>>> >>>>> This patch adds a "pmu-passthrough" property to X86CPU, and set it to >>>>> true only on "-cpu host", or on pc-*-1.5 and older machine-types. >>>> >>>> Can we just call the property "pmu"? It doesn't have to be passthough. >>> >>> Yes, but the only options we have today are "no PMU" and "passthrough >>> PMU". I wouldn't like to make "pmu=on" enable the passthrough behavior >>> implicitly (I don't want things that break live-migration to be enabled >>> without making it explicit that it is a host-dependent/passthrough >>> mode). >> >> I think "passthrough PMU" should be considered a bug except of course >> with "-cpu host". >> >> If "-cpu Nehalem,pmu=on" goes from passthrough to Nehalem-compatible in >> a future QEMU release, that'll be a bugfix. > > Exactly. But then I don't understand your suggestion. We still need a > property to enable pasthrough behavior on old machine-types (not > perfect, but a best-effort way to try to keep compatibility),
Do we? We only need "pmu=on"---which right now is buggy on old machine types because it will always passthrough. Paolo > and I > named that option "pmu-passthrough". How do you think we should name it?
