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Re: [PATCH v15 21/23] hw/core/cpu: call qemu_init_vcpu in cpu_common_rea

From: Claudio Fontana
Subject: Re: [PATCH v15 21/23] hw/core/cpu: call qemu_init_vcpu in cpu_common_realizefn
Date: Thu, 4 Feb 2021 11:23:52 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0

On 2/3/21 5:51 PM, Alex Bennée wrote:
> Claudio Fontana <cfontana@suse.de> writes:
>> move the call to qemu_init_vcpu inside cpu_common_realizefn,
>> so it does not need to be done explicitly in each target cpu.
>> Despite this, the way cpu realize is done continues to be not ideal;
>> ideally the cpu_list_add would be done in common_cpu,
>> and in this case we could avoid even more redundant open coded
>> additional calls in target/xxx/cpu.c,
>> but this cannot happen because target cpu code, plugins, etc
>> now all came to rely on cpu->index
>> (which is updated in cpu_list_add), since no particular order
>> was defined previously, so we are stuck with the freak call
>> order for the target cpu realizefn.
>> After this patch the target/xxx/cpu.c realizefn body becomes:
>> void mycpu_realizefn(DeviceState *dev, Error **errp)
>> {
>>     /* ... */
>>     cpu_exec_realizefn(CPU_STATE(dev), errp);
>>     /* ... anything that needs done pre-qemu_vcpu_init */
>>     xcc->parent_realize(dev, errp); /* does qemu_vcpu_init */
>>     /* ... anything that needs to be done after qemu_vcpu_init */
>> }
> Uggh, introducing a magic order seems like inviting trouble for later
> on. Is there anyway we can improve things? Paolo?

The magic order is there already. I call it "freak order" instead of "magic", 
because this is more the result of uncontrolled code growth rather than the 
work of magic :-)

This patch attempts to remove one degree of freedom, but the current situation 
of cpu realizing is basically fubar. This patch attempts to improve things 
but as mentioned elsewhere it basically fails to achieve the goal,

so I am tempted to just retire it. Maybe someone interested could look at the 
situation with new eyes (possibly even me later on).



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