Re: [RFC v5 11/12] i386: centralize initialization of cpu accel interfaces

[Eduardo Habkost]

On Thu, Nov 26, 2020 at 03:33:17PM +0100, Claudio Fontana wrote:
> On 11/26/20 2:44 PM, Eduardo Habkost wrote:
> > On Thu, Nov 26, 2020 at 11:57:28AM +0100, Claudio Fontana wrote:
> >> On 11/24/20 10:31 PM, Eduardo Habkost wrote:
> >>> On Tue, Nov 24, 2020 at 09:13:13PM +0100, Paolo Bonzini wrote:
> >>>> On 24/11/20 17:22, Claudio Fontana wrote:
> >>>>> +static void x86_cpu_accel_init(void)
> >>>>>  {
> >>>>> -    X86CPUAccelClass *acc;
> >>>>> +    const char *ac_name;
> >>>>> +    ObjectClass *ac;
> >>>>> +    char *xac_name;
> >>>>> +    ObjectClass *xac;
> >>>>> -    acc = X86_CPU_ACCEL_CLASS(object_class_by_name(accel_name));
> >>>>> -    g_assert(acc != NULL);
> >>>>> +    ac = object_get_class(OBJECT(current_accel()));
> >>>>> +    g_assert(ac != NULL);
> >>>>> +    ac_name = object_class_get_name(ac);
> >>>>> +    g_assert(ac_name != NULL);
> >>>>> -    object_class_foreach(x86_cpu_accel_init_aux, TYPE_X86_CPU, false, 
> >>>>> &acc);
> >>>>> +    xac_name = g_strdup_printf("%s-%s", ac_name, TYPE_X86_CPU);
> >>>>> +    xac = object_class_by_name(xac_name);
> >>>>> +    g_free(xac_name);
> >>>>> +
> >>>>> +    if (xac) {
> >>>>> +        object_class_foreach(x86_cpu_accel_init_aux, TYPE_X86_CPU, 
> >>>>> false, xac);
> >>>>> +    }
> >>>>>  }
> >>>>> +
> >>>>> +accel_cpu_init(x86_cpu_accel_init);
> >>>>
> >>>> If this and cpus_accel_ops_init are the only call to accel_cpu_init, I'd
> >>>> rather make them functions in CPUClass (which you find and call via
> >>>> CPU_RESOLVING_TYPE) and AccelClass respectively.
> >>>
> >>> Making x86_cpu_accel_init() be a CPUClass method sounds like a
> >>> good idea.  This way we won't need a arch_cpu_accel_init() stub
> >>> for non-x86.
> >>>
> >>> accel.c can't use cpu.h, correct?  We can add a:
> >>>
> >>>   CPUClass *arch_base_cpu_type(void)
> >>>   {
> >>>       return object_class_by_name(CPU_RESOLVING_TYPE);
> >>>   }
> >>>
> >>> function to arch_init.c, to allow target-independent code call
> >>> target-specific code.
> >>>
> >>
> >> Hi Eduardo,
> >>
> >> we can't use arch-init because it is softmmu only, but we could put this 
> >> in $(top_srcdir)/cpu.c
> > 
> > That would work, too.
> > 
> >>
> >> however, it would be very useful to put a:
> >>
> >> #define TYPE_ACCEL_CPU "accel-" CPU_RESOLVING_TYPE
> >> #define ACCEL_CPU_NAME(name) (name "-" TYPE_ACCEL_CPU)
> >>
> >> in an H file somewhere, for convenience for the programmer that
> >> has to implement subclasses in target/xxx/
> > 
> > Absolutely.
> > 
> >>
> >> But it is tough to find a header where CPU_RESOLVING_TYPE can be used.
> > 
> > cpu-all.h?
> > 
> >>
> >> We could I guess just use plain "cpu" instead of CPU_RESOLVING_TYPE,
> >> maybe that would be acceptable too? The interface ends up in CPUClass, so 
> >> maybe ok?
> >>
> >> So we'd end up having
> >>
> >> accel-cpu
> >>
> >> instead of the previous
> >>
> >> accel-x86_64-cpu
> >>
> >> on top of the hierarchy.
> > 
> > It seems OK to have a accel-cpu type at the top, but I don't see
> > why it solves the problem above.  What exactly would be the value
> > of `kvm_cpu_accel.name`?
> > 
> 
> It does solve the problem, because we can put then all AccelOpsClass and 
> AccelCPUClass stuff in accel.h,
> resolve everything in accel/accel-*.c, and make a generic solution fairly 
> self-contained (already tested, will post soonish).
> 
> But I'll try cpu-all.h if it's preferred to have accel-x86_64-cpu, 
> accel-XXX-cpu on top, I wonder what the preference would be?

I don't have a specific preference, but I still wonder how
exactly you would name the X86CPUAccel implemented at
target/i386/kvm, and how exactly you would look for it when
initializing the accelerator.

-- 
Eduardo