On Thu, 13 Feb 2025 12:48:30 +0100
Markus Armbruster <arm...@redhat.com> wrote:
> gaosong <gaos...@loongson.cn> writes:
>
> > Cc: Markus
> >
> > hi, Markus
> >
> > What is the difference between CPU_MODEL_EXPANSION_TYPE_STATIC and
> > CPU_MODEL_EXPANSION_TYPE_FULL?
the only difference is that 'static' expansion will not report properties
not mentioned in hard-codded CPU model definition see: builtin_x86_defs
while 'full' will iterate over/report all rw properties of CPU object
created from provided model name.
> I don't know :)
>
> Here's the documentation:
>
> ##
> # @CpuModelExpansionType:
> #
> # An enumeration of CPU model expansion types.
> #
> # @static: Expand to a static CPU model, a combination of a static
> # base model name and property delta changes. As the static base
> # model will never change, the expanded CPU model will be the
> # same, independent of QEMU version, machine type, machine
> # options, and accelerator options. Therefore, the resulting
> # model can be used by tooling without having to specify a
> # compatibility machine - e.g. when displaying the "host" model.
> # The @static CPU models are migration-safe.
Looking at related x86 code above description sounds like a fiction.
Both 'static' and 'full' do use
qmp_query_cpu_model_expansion()
x86_cpu_from_model()
cpu = object_new(foo_cpu_class)
x86_cpu_expand_features(cpu)
and the later 2 calls are subjects to being influenced by:
"QEMU version, machine type (compat machinery), machine options, and
accelerator options"
and -cpu option
> #
> # @full: Expand all properties. The produced model is not guaranteed
> # to be migration-safe, but allows tooling to get an insight and
> # work with model details.
> #
> # .. note:: When a non-migration-safe CPU model is expanded in static
> # mode, some features enabled by the CPU model may be omitted,
> # because they can't be implemented by a static CPU model
> # definition (e.g. cache info passthrough and PMU passthrough in
> # x86). If you need an accurate representation of the features
> # enabled by a non-migration-safe CPU model, use @full. If you
> # need a static representation that will keep ABI compatibility
> # even when changing QEMU version or machine-type, use @static (but
> # keep in mind that some features may be omitted).
> #
> # Since: 2.8
> ##
>
> If you have further questions, David Hildenbrand or Eduardo Habkost
> (cc'ed) might be able to help.
>
>
