Re: [Qemu-devel] [PATCH 07/23] target-i386: convert cpuid features into properties

[Eduardo Habkost]

On Thu, Oct 04, 2012 at 03:25:59PM +0200, Igor Mammedov wrote:
> On Thu, 4 Oct 2012 10:10:27 -0300
> Eduardo Habkost <address@hidden> wrote:
> 
> > On Thu, Oct 04, 2012 at 03:01:19PM +0200, Igor Mammedov wrote:
> > > On Thu, 4 Oct 2012 09:43:41 -0300
> > > Eduardo Habkost <address@hidden> wrote:
> > > 
> > > > On Thu, Oct 04, 2012 at 08:53:22AM +0200, Igor Mammedov wrote:
> > > > > On Wed, 3 Oct 2012 13:54:34 -0300
> > > > > Eduardo Habkost <address@hidden> wrote:
> > > > > 
> > > > > > On Wed, Oct 03, 2012 at 06:24:11PM +0200, Igor Mammedov wrote:
> > > > > > > On Wed, 03 Oct 2012 17:20:46 +0200
> > > > > > > Paolo Bonzini <address@hidden> wrote:
> > > > > > > 
> > > > > > > > Il 03/10/2012 17:03, Eduardo Habkost ha scritto:
> > > > > > > > > On Tue, Oct 02, 2012 at 05:38:45PM -0300, Eduardo Habkost
> > > > > > > > > wrote:
> > > > > > > > >> (Now replying on the right thread, to keep the discussion in
> > > > > > > > >> the right place. I don't know how I ended up replying to a
> > > > > > > > >> pre-historic version of the patch, sorry.)
> > > > > > > > >>
> > > > > > > > >> On Tue, Oct 02, 2012 at 05:36:59PM +0200, Igor Mammedov
> > > > > > > > >> wrote: [...]
> > > > > > > > >>> @@ -1938,6 +2043,12 @@ static void x86_cpu_initfn(Object
> > > > > > > > >>> *obj) object_property_add(obj, "tsc-frequency", "int",
> > > > > > > > >>>                          x86_cpuid_get_tsc_freq,
> > > > > > > > >>>                          x86_cpuid_set_tsc_freq, NULL, NULL,
> > > > > > > > >>> NULL);
> > > > > > > > >>> +    x86_register_cpuid_properties(obj, feature_name);
> > > > > > > > >>> +    x86_register_cpuid_properties(obj, ext_feature_name);
> > > > > > > > >>> +    x86_register_cpuid_properties(obj, ext2_feature_name);
> > > > > > > > >>> +    x86_register_cpuid_properties(obj, ext3_feature_name);
> > > > > > > > >>> +    x86_register_cpuid_properties(obj, kvm_feature_name);
> > > > > > > > >>> +    x86_register_cpuid_properties(obj, svm_feature_name);
> > > > > > > > >>
> > > > > > > > >> Stupid question about qdev:
> > > > > > > > >>
> > > > > > > > >> - qdev_prop_set_globals() is called from device_initfn()
> > > > > > > > >> - device_initfn() is called before the child class
> > > > > > > > >> instance_init() function (x86_cpu_initfn())
> > > > > > > > >> - So, qdev_prop_set_globals() gets called before the CPU
> > > > > > > > >> class properties are registered.
> > > > > > > > >>
> > > > > > > > >> So this would defeat the whole point of all the work we're
> > > > > > > > >> doing, that is to allow compatibility bits to be set as
> > > > > > > > >> machine-type global properties. But I don't know what's the
> > > > > > > > >> right solution here.
> > > > > > > > >>
> > > > > > > > >> Should the qdev_prop_set_globals() call be moved to
> > > > > > > > >> qdev_init() instead? Should the CPU properties be registered
> > > > > > > > >> somewhere else?
> > > > > > > > 
> > > > > > > > Properties should be registered (for all objects, not just
> > > > > > > > CPUs) in the instance_init function.  This is device_initfn.
> > > > > > > > 
> > > > > > > > I would add an instance_postinit function that is called at the
> > > > > > > > end of object_initialize_with_type, that is after
> > > > > > > > instance_init, and in the opposite order (i.e. from the leaf to
> > > > > > > > the root).
> > > > > > > 
> > > > > > > You've meant something like that?
> > > > > > > 
> > > > > > 
> > > > > > That's almost exactly the same code I wrote here. :-)
> > > > > > 
> > > > > > The only difference is that I added post_init to the struct Object
> > > > > > documentation comments, and added a unit test. The unit test
> > > > > > required the qdev-core/qdev split, so we could compile it without
> > > > > > bringing too many dependencies. I will submit it soon.
> > > > > > 
> > > > > After irc discussion, Anthony suggested to use static properties
> > > > > instead of dynamic ones that we use now. 
> > > > > 
> > > > > But  qdev_prop_set_globals() in device_initfn() is still causes
> > > > > problems even with static properties.
> > > > > 
> > > > > For x86 CPU classes we were going dynamically generate CPU classes and
> > > > > store pointer to appropriate cpudef from builtin_x86_defs in class
> > > > > field for each CPU class and then init default feature words values
> > > > > from this field int x86_cpu_initfn().
> > > > > 
> > > > > However with qdev_prop_set_globals() in device_initfn() that is called
> > > > > before x86_cpu_initfn() it won't work because defaults in
> > > > > x86_cpu_initfn() will overwrite whatever was set by
> > > > > qdev_prop_set_globals().
> > > > 
> > > > We can set the default values on class_init, instead. The class_init
> > > > function for each CPU model can get the x86_def_t struct as the data
> > > > pointer.
> > > > 
> > > > I still think that the interface to build the DeviceClass.props array on
> > > > class_init is really painful to use, but it's still doable.
> > > 
> > > You mean dynamic building of DeviceClass.props arrays for each CPU
> > > sub-class?
> > 
> > That's the only solution I see if we want to make all the CPU properties
> > static, yes.
> 
> Well I could generate compile time arrays for every built-in cpu model
> and we can remove then x86_def_t struct & builtins altogether.
> Only 'host' would be left for dynamic generation then.

You mean duplicating the property list in the code? Then the
feature-name -> CPUID-bit mapping information would be duplicated on all
those arrays, and adding support to a new CPU feature would require
adding entries to all the arrays.


> 
> > 
> > I'm still not convinced we really need to do that, though. Maybe we can
> > make static only the ones we really need to be able to implement
> > machine-type-compatibility global properties?
> > 
> > Machine-type compatibility global properties were the initial reason for
> > the static-properties requirement. We don't really need to allow _all_
> > CPU features to be controlled by global properties, only the ones we
> > need for machine-type compatibility.
> > 
> 

-- 
Eduardo