On Tue, Dec 13, 2016 at 10:47:38AM +0100, Markus Armbruster wrote:
> I'm not familiar with CPU model expansion, but here goes anyway.
>
> Eduardo Habkost <ehabkost@xxxxxxxxxx> writes:
>
> > On x86, "-cpu host" enables some features that can't be
> > represented by a static CPU model definition: cache info
> > passthrough ("host-cache-info") and PMU passthrough ("pmu"). This
> > means a type=static expansion of "host" can't include those
> > features.
> >
> > A type=full expansion of "host", on the other hand, can include
> > those features, but then the returned data won't be a static CPU
> > model representation.
> >
> > Add a note to the documentation explaining that when using CPU
> > models that include non-migration-safe features, users need to
> > choose being precision and safety: a precise expansion of the CPU
>
> s/being/between/
>
> > model (full) won't be safe (static), (because they would include
>
> s/they/it/
Oops. Thanks!
>
> > pmu=on and host-cache-info=on), and a safe (static) expansion of
> > the CPU model won't be precise.
> >
> > Architectures where CPU model expansion is always migration-safe
> > (e.g. s390x) can simply do what they already do, and set
> > 'migration-safe' and 'static' to true.
>
> This patch does that exactly for s390x. The next patch looks like it
> does something for x86. What about other targets? I recommend to have
> this commit message explain briefly what this patch does, what later
> patches in this series do, and what's left for later (if anything).
s390x is the only architecture implementing
query-cpu-model-expansion by now.
I will add a comment clarifying that, anyway.
>
> > Cc: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
> > Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> > Cc: David Hildenbrand <david@xxxxxxxxxx>
> > Cc: libvir-list@xxxxxxxxxx
> > Cc: Jiri Denemark <jdenemar@xxxxxxxxxx>
> > Cc: "Jason J. Herne" <jjherne@xxxxxxxxxxxxxxxxxx>
> > Cc: Markus Armbruster <armbru@xxxxxxxxxx>
> > Cc: Eric Blake <eblake@xxxxxxxxxx>
> > Signed-off-by: Eduardo Habkost <ehabkost@xxxxxxxxxx>
> > ---
> > qapi-schema.json | 25 ++++++++++++++++++++++++-
> > target-s390x/cpu_models.c | 4 ++++
> > 2 files changed, 28 insertions(+), 1 deletion(-)
> >
> > diff --git a/qapi-schema.json b/qapi-schema.json
> > index 8d113f8..a102534 100644
> > --- a/qapi-schema.json
> > +++ b/qapi-schema.json
> > @@ -3291,6 +3291,15 @@
> > # 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: 2.8.0
> > ##
> > { 'enum': 'CpuModelExpansionType',
> > @@ -3304,10 +3313,24 @@
> > #
> > # @model: the expanded CpuModelInfo.
> > #
> > +# @migration-safe: the expanded CPU model in @model is a migration-safe
> > +# CPU model. See @CpuDefinitionInfo.migration-safe.
> > +# If expansion type was @static, this is always true.
> > +# (since 2.9)
> > +#
> > +# @static: the expanded CPU model in @model is a static CPU model.
> > +# See @CpuDefinitionInfo.static. If expansion type was @static,
> > +# this is always true.
> > +# (since 2.9)
> > +#
> > +# query-cpu-model-expansion with static expansion type should always
> > +# return a static and migration-safe expansion.
> > +#
> > # Since: 2.8.0
> > ##
> > { 'struct': 'CpuModelExpansionInfo',
> > - 'data': { 'model': 'CpuModelInfo' } }
> > + 'data': { 'model': 'CpuModelInfo', 'static': 'bool',
> > + 'migration-safe': 'bool' } }
> >
> >
> > ##
> > diff --git a/target-s390x/cpu_models.c b/target-s390x/cpu_models.c
> > index 5b66d33..f934add 100644
> > --- a/target-s390x/cpu_models.c
> > +++ b/target-s390x/cpu_models.c
> > @@ -448,6 +448,10 @@ CpuModelExpansionInfo *arch_query_cpu_model_expansion(CpuModelExpansionType type
> > /* convert it back to a static representation */
> > expansion_info = g_malloc0(sizeof(*expansion_info));
> > expansion_info->model = g_malloc0(sizeof(*expansion_info->model));
> > +
> > + /* We always expand to a static and migration-safe CpuModelInfo */
> > + expansion_info->q_static = true;
> > + expansion_info->migration_safe = true;
> > cpu_info_from_model(expansion_info->model, &s390_model, delta_changes);
> > return expansion_info;
> > }
--
Eduardo
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