Manuel Bouyer wrote:

>On Wed, May 24, 2006 at 05:38:54PM +0200, Hubert Feyrer wrote:
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>>On Wed, 24 May 2006, Tillman Hodgson wrote:
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>>
>>>Is building a custom Xen kernel for this as easy as adding in the
>>>GENERIC.MP changes and something like this for device support?:
>>>      
>>>
>>Read http://www.netbsd.org/Ports/xen/howto.html#pci-devices
>>    
>>
>
>I'd add that using a recent XEN0 kernel from the netbsd-3 branch should
>have the drivers for this hardware. This has been added some weeks ago.
>
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>>As for SMP, I'm not sure if Xen2 supports that.
>>Support for Xen3 domU and I think dom0 is in -current. (there may be some 
>>code on the netbsd-3 branch, but I forgot)
>>    
>>
>
>With Xen2, multiple CPUs can't be used by a single domain, but if you
>have multiple domains running, the hypervisor will schedule them on different
>CPUs.
>The assignement is done on domain startup, you can't move a domain from one
>CPU to another once started.
>
>With Xen3, it's theorically possible to have one domain use multiple CPUs
>but NetBSD doesn't support that yet. I suspect the hypervisor can move
>domains from one cpu to another dynamically but I didn't try this.
>
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Xen 3 can *theorically* change CPU<->VCPU assignement while running, but 
the actual schedulers don't implement this. A new one is in test though, 
available in the lastest version of Xen (unstable ones, need to checkout 
and build sources). Use "sched=credit" on the command line. Note that i 
haven't tested it nor seen any feedback on this, it's fairly new...
As a side note, i'd like to add that the current interrupt model in Xen 
is pretty weak in some cases. As all interrupts are routed to VCPU0, a 
machine with high interrupt load (like a router or a fileserver) will 
have CPU0 at about 100% load all the time while all others will remain idle.