Re: [Qemu-devel] [RFC PATCH v0 2/9] cpu: Store CPU typename in MachineState

[Eduardo Habkost]

On Wed, Dec 16, 2015 at 05:54:25PM +0100, Igor Mammedov wrote:
> On Tue, 15 Dec 2015 14:08:09 +0530
> Bharata B Rao <address@hidden> wrote:
> 
> > On Mon, Dec 14, 2015 at 03:29:49PM -0200, Eduardo Habkost wrote:
> > > On Thu, Dec 10, 2015 at 11:45:37AM +0530, Bharata B Rao wrote:
> > > > Storing CPU typename in MachineState lets us to create CPU threads
> > > > for all architectures in uniform manner from arch-neutral code.
> > > > 
> > > > TODO: Touching only i386 and spapr targets for now
> > > > 
> > > > Signed-off-by: Bharata B Rao <address@hidden>
> > > 
> > > Suggestions:
> > > 
> > > * Name the field "cpu_base_type" to indicate it is the base CPU
> > >   class name, not the actual CPU class name used when creating
> > >   CPUs.
> > > * Put it in MachineClass, as it may be useful for code that
> > >   runs before machine->init(), in the future.
> > 
> > Ok.
> > 
> > > * Maybe make it a CPUClass* field instead of a string?
> > 
> > In the current use case, this base cpu type string is being passed
> > to cpu_generic_init(const char *typename, const char *cpu_model)
> > to create boot time CPUs with given typename and cpu_mode. So for now
> > the string makes sense for use case.
> > 
> > Making it CPUClass* would necessiate more changes to
> > cpu_generic_init().
> how about actually leaving it as "cpu_type" and putting in it
> actual cpu type that could be used with device_add().
> 
> that would get rid of keeping and passing around intermediate cpu_model.

Makes sense. We only need to save both typename and cpu_model
today because cpu_generic_init() currently encapsulates three
steps: CPU class lookup + CPU creation + CPU feature parsing. But
we shouldn't need to redo CPU class lookup every time.

We could just split cpu_model once, and save the resulting
CPUClass* + featurestr, instead of saving the full cpu_model
string and parsing it again every time.

The only problem is that it would require refactoring multiple
machines/architectures that use a cpu_XXX_init(const char *cpu_model)
helper.

-- 
Eduardo