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

[Eduardo Habkost]

On Thu, Nov 26, 2020 at 03:55:37PM +0100, Claudio Fontana wrote:
> On 11/26/20 3:49 PM, Eduardo Habkost wrote:
> > 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.
> > 
> 
> If we agree to use "accel-cpu" I would lookup "kvm-accel-cpu"

The structure in target/i386/kvm is x86-specific and
kvm-specific.  If we name it "kvm-accel-cpu", how would you name
the equivalent structures at target/s390x/kvm, target/arm/kvm,
target/ppc/kvm?

The same question would apply to target/*/tcg*, and to other
accelerators.

> if we agree to use "accel-x86_64" aka "accel-" CPU_RESOLVING_TYPE, I would 
> lookup "kvm-accel-" CPU_RESOLVING_TYPE
> 
> * initialize the arch-specific accel CpuClass interfaces */
> static void accel_init_cpu_interfaces(AccelClass *ac, const char *cpu_type)
> {
>     const char *ac_name; /* AccelClass name */
>     char *acc_name;      /* AccelCPUClass name */
>     ObjectClass *acc;    /* AccelCPUClass */
> 
>     ac_name = object_class_get_name(OBJECT_CLASS(ac));
>     g_assert(ac_name != NULL);
> 
>     acc_name = g_strdup_printf("%s-cpu", ac_name);
>     acc = object_class_by_name(acc_name);
>     g_free(acc_name);
> 
>     if (acc) {
>         object_class_foreach(accel_init_cpu_interfaces_aux, cpu_type, false, 
> acc);
>     }
> }
> 
> Ciao,
> 
> CLaudio
> 

-- 
Eduardo