Re: [Qemu-devel] [PATCH 1/7] Introduce a new bus "ICC" to connect APIC

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-02-16 13:59, Anthony Liguori wrote:
> On 02/16/2012 06:50 AM, Jan Kiszka wrote:
>> On 2012-02-16 13:42, Anthony Liguori wrote:
>>> On 02/16/2012 05:25 AM, Jan Kiszka wrote:
>>>> On 2012-02-16 00:16, Igor Mammedov wrote:
>>>>> Introduce a new structure CPUS as the controller of ICC (INTERRUPT
>>>>> CONTROLLER COMMUNICATIONS), and new bus "ICC" to hold APIC,instead
>>>>> of sysbus. So we can support APIC hot-plug feature.
>>>>>
>>>>> This is repost of original patch for qemu-kvm rebased on current qemu:
>>>>> http://lists.nongnu.org/archive/html/qemu-devel/2011-11/msg01478.html
>>>>> All credits to Liu Ping Fan for writing it.
>>>>>
>>>>> V2 changes:
>>>>>     - cpusockets_init: cpu_sockets is not yet initialized, use cpus that
>>>>>       we got as input param instead for qbus_create, this makes cpus
>>>>>       apics visible in "info qtree" monitor command
>>>>>     - fix format error spotted by Jan and missed by checkpatch
>>>>>     - cpu_has_apic_feature: return bool instead of int
>>>>>
>>>>
>>>> This patch surely no longer applies. And the ICC requires QOM conversion.
>>>
>>> Also, post-QOM, I don't think having an ICC bus makes a whole lot of sense.
>>>
>>> The LAPIC can be made a child of the CPU device with a bidirectional link.
>>
>> We do have a bus here, the IO-APICs are attached to it as well.
> 
> 
> Isn't that a bus protocol that's specific to the LAPICs/IO-APICs?  I don't think 
> that you would logically model the CPU as part of it.

Actually, MSIs go this way as well.

> 
> I wonder if modeling inter-lapic communication via a bus is a bit overkill 
> compared to what we do today (just a for() loop when needed).

For sure, we can keep such loops for all those use case. But Andreas may
have a different vision as he wanted to eliminate (public) first_cpu
references.

Jan

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