Re: [PATCH]0/2 Patches to furthure split kvm_init

[Christian Ehrhardt <ehrhardt-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>]

Avi Kivity wrote:
> Zhang, Xiantao wrote:
>> Avi Kivity wrote:
>>   
>>> Zhang, Xiantao wrote:
>>>     
>>>> Avi Kivity wrote:
>>>>
>>>>       
>>>>> Christian Ehrhardt wrote:
>>>>>
>>>>>         
>>>>>> Hi Xiantao,
>>>>>> it looks good to me to move kvm_vcpu_cache out to the x86 specific
>>>>>> code 
>>>>>>
>>>>>>           
>>>>> Why is that?  Do other archs not want kvm_vcpu_cache, or is it just
>>>>> the alignment? 
>>>>>
>>>>>         
>>>> At lease we didn't fall across the similar requirements about such
>>>> alignment issues in IA64. 
>>>>
>>>>       
>>> What I mean is, other archs do require kvm_vcpu_cache (without the
>>> alignment), so why move the code?  Just make the alignment arch
>>> dependent with a #define.
>>>     
>> I think IA64 TOTALLY doen't need this logic, so do the move:)
>>
>>   
> 
> Ah, I see.  It isn't just the alignment. How do you allocate kvm_vcpu, then?
> 
> 
> What about s390 and powerpc?  I imagine they don't have an alignment
> issue, but do they have a totally unique way of allocating vcpus as well?

On one hand we don't have "these" alignment issues, but on the other hand we have some complex offset logic to integrate structures and handler vectors&code (which need special alignment).
The major problem is that the our prototype currently only supports one vcpu per guest and therefore we didn't think a lot about e.g. kmem_cache for vcpu structures.
>From my current point of view we may be able to use a kmem_cache and be able to do all sophisticated ppc stuff in an arch function filling the arch part of vcpu, but that opinion may change when we look further into it while implementing muli-vcpu support per guest.
Because of that I think atm your CONFIG_HAVE_SPECIAL_VCPU_ALLOC suggestion would be nice, with that we could do either way later without restructuring the generic code too much.

I added Hollis to the direct CC List, because this ppc code is his creation he might be able to give us a much clearer insight how ppc vcpu allocation in future might look like.

> Maybe we should just #ifndef CONFIG_IA64 (or #ifdef
> CONFIG_HAVE_SPECIAL_VCPU_ALLOC) this bit instead of duplicating it for
> s390 and ppc.
> 


-- 

Grüsse / regards, 
Christian Ehrhardt

IBM Linux Technology Center, Open Virtualization
+49 7031/16-3385
Ehrhardt-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org
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