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

[Claudio Fontana]

On 11/26/20 4:14 PM, Eduardo Habkost wrote:
> 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 way; only one of them would be compiled into the target binary, so the 
lookup would not collide in practice,
but I wonder whether we want separate names anyway.

Ciao,

Claudio

> 
> 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
>>
>