RE: [Xen-ia64-devel][PATCH] Enable SMP on VTI domain.

["Xu, Anthony" <anthony.xu@xxxxxxxxx>]

>From: Tristan Gingold [mailto:Tristan.Gingold@xxxxxxxx]
>Sent: 2006年5月31日 17:43
>To: Xu, Anthony; xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
>Subject: Re: [Xen-ia64-devel][PATCH] Enable SMP on VTI domain.
>
>Le Mercredi 31 Mai 2006 11:08, Xu, Anthony a écrit :
>> From: Tristan Gingold
>>
>> >Sent: 2006年5月31日 17:01
>> >
>> >> >I think Xen can
>> >> >impose lid to the guest firmware.  Things will be a little simpler.
>> >>
>> >> I don't catch you, Could you explain in more detail?
>> >
>> >I think lid_2_vcpu is almost useless.  Like in paravirtualized, vcpuid
>> > should be simply extracted from lid.
>>
>> You mean vcpuid is extracted from machine lid.
>Yes.
>
>> It may work for domU, because lsapic table is built by xen.
>> But for VTI-domain, lsapic table is built by guest firmware, how can
>> guest firmware get other LP's lid.
>Same as on a real machine: SAL has to know LP's lid.
>I simply think lids must be 0, 1, 2...
Yes, you are right....

Current implement is as below,
Only vcpu0 executes guest firmware, and other vcpus don't execute guest 
firmware.

The reason is as below,
There is below scenarios,
We configure 8 vcpus for a domain, but guest OS on this domain only supports 4 
vcpus, the other 4 vcpus are not used.
And now VTI-domain uses per-VCPU vtlb, that means there are 4 per-VCPU vtlbs
allocated, but not used. It will waste many memory.
So current algorithm is, only when Guest OS wants to wake up a vcpu, the 
per-VCPU
Vtlb for this vcpu is allocated.

>
>> So in VTI-domain, we should use vcpuid predefined by XEN and guest
>> firmware.
>Why can't they match ?
>
>> Another concern is,
>> If SMP guest is running on a UP platform, vcpus may have same vcpuid.
>Why ?  IMHO this can never happen.
There are 4 LP on my box, if I want to boot a domU with 6 vcpus,
Can this domU boot?


>
>Tristan.

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