Re: [Qemu-devel] [PATCH for-1.4 07/12] target-i386/cpu: Introduce apic_id_for_cpu() function

[Andreas Färber]

Am 21.01.2013 12:31, schrieb Eduardo Habkost:
> On Mon, Jan 21, 2013 at 12:18:55PM +0100, Andreas Färber wrote:
>> Am 17.01.2013 21:59, schrieb Eduardo Habkost:
>>> This function will be used by both the CPU initialization code and the
>>> fw_cfg table initialization code.
>>>
>>> Later this function will be updated to generate APIC IDs according to
>>> the CPU topology.
>>>
>>> Signed-off-by: Eduardo Habkost <address@hidden>
>>> ---
>>>  target-i386/cpu.c | 17 ++++++++++++++++-
>>>  target-i386/cpu.h |  2 ++
>>>  2 files changed, 18 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
>>> index d1a14d5..d90789d 100644
>>> --- a/target-i386/cpu.c
>>> +++ b/target-i386/cpu.c
>>> @@ -2194,6 +2194,21 @@ void x86_cpu_realize(Object *obj, Error **errp)
>>>      cpu_reset(CPU(cpu));
>>>  }
>>>  
>>> +/* Calculates initial APIC ID for a specific CPU index
>>> + *
>>> + * Currently we need to be able to calculate the APIC ID from the CPU index
>>> + * alone (without requiring a CPU object), as the QEMU<->Seabios 
>>> interfaces have
>>> + * no concept of "CPU index", and the NUMA tables on fw_cfg need the APIC 
>>> ID of
>>> + * all CPUs up to max_cpus.
>>> + */
>>> +uint32_t apic_id_for_cpu(unsigned int cpu_index)
>>
>> Can we rather make this x86_cpu_apic_id(X86CPU *cpu) to account for
>> future changes to topology modelling?
> 
> We can't make it get a X86CPU as parameter, because the ACPI tables have
> to be built up to max_cpus, before the CPUs get actually created. But it
> can be renamed, yes.

I see. Is this a limitation of the current code?

IIUC the cpu_index is set once during qemu_init_vcpu() by counting the
CPUArchStates in the first_cpu list. So if we hot-unplug a non-last CPU
this is gonna result in chaos. Therefore I was hoping we could do
something more clever than hardcoding cpu_index in our internal API ...
but we can refactor that as follow-up when the need comes up.

Andreas

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