Re: [PATCH-for-9.0?] docs: i386: pc: Update maximum CPU numbers for PC Q35

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 4/6/24 10:54, Zhao Liu wrote:
> On Mon, Jun 03, 2024 at 07:31:47PM +0200, Philippe Mathieu-Daudé wrote:
>> Date: Mon, 3 Jun 2024 19:31:47 +0200
>> From: Philippe Mathieu-Daudé <philmd@linaro.org>
>> Subject: Re: [PATCH-for-9.0?] docs: i386: pc: Update maximum CPU numbers
>>   for PC Q35
>>
>> Hi Michael,
>>
>> On 2/6/24 15:30, Michael S. Tsirkin wrote:
>>> On Fri, Apr 12, 2024 at 11:57:35AM +0200, Philippe Mathieu-Daudé wrote:
>>>> Hi Zhao,
>>>>
>>>> On 12/4/24 10:53, Zhao Liu wrote:
>>>>> From: Zhao Liu <zhao1.liu@intel.com>
>>>>>
>>>>> Commit e4e98c7eebfa ("pc: q35: Bump max_cpus to 4096 vcpus") increases
>>>>> the supported CPUs for PC Q35 machine.
>>>>>
>>>>> Update maximum CPU numbers for PC Q35 in the document.
>>>>>
>>>>> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
>>>>> ---
>>>>>     docs/system/target-i386-desc.rst.inc | 2 +-
>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/docs/system/target-i386-desc.rst.inc b/docs/system/target-i386-desc.rst.inc
>>>>> index 5ebbcda9db4c..319e540573d3 100644
>>>>> --- a/docs/system/target-i386-desc.rst.inc
>>>>> +++ b/docs/system/target-i386-desc.rst.inc
>>>>> @@ -36,7 +36,7 @@ The QEMU PC System emulator simulates the following peripherals:
>>>>>     -  PCI UHCI, OHCI, EHCI or XHCI USB controller and a virtual USB-1.1
>>>>>        hub.
>>>>> -SMP is supported with up to 255 CPUs.
>>>>> +SMP is supported with up to 255 CPUs (and 4096 CPUs for PC Q35 machine).
>>>>
>>>> This comment is not accurate since a while, IIUC:
>>>>
>>>> Up to q35-2.7: 255
>>>> q35-2.8: 288
>>>> q35-8.0+: 1024
>>>> q35-9.0: 4096
>>>
>>>
>>> What are you saying here, Philippe? I don't think compat
>>> machine types matter enough to bother with more detail.
>>
>> My point is I find this description confusing w.r.t. how QEMU behaves:
>>
>> $ qemu-system-i386 -M pc-q35-2.8 -smp 666
>> qemu-system-i386: Invalid SMP CPUs 666. The max CPUs supported by machine
>> 'pc-q35-2.8' is 288
>>
>> $ qemu-system-i386 -M pc-q35-8.0 -smp 666
>> qemu-system-i386: Invalid SMP CPUs 666. The max CPUs supported by machine
>> 'pc-q35-8.0' is 288
>>
>> $ qemu-system-i386 -M pc-q35-9.0 -smp 666
>> Unexpected error in apic_common_set_id() at ../hw/intc/apic_common.c:447:
>> qemu-system-i386: APIC ID 255 requires x2APIC feature in CPU
>> Abort trap: 6
> 
> For tcg, it needs to set x2apic=on in -cpu.

Thanks for clarifying. Using error_append_hint() is certainly
better than aborting or asking on the mailing list (from user
perspective) ;)

Regards,

Phil.