Re: [Xen-devel] [PATCH][v2] Hybrid extension support in Xen

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 02/02/2010 14:32, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:

>>> Okay, so that leads to the obvious next question: why do you want to avoid
>>> using INIT-SIPI-SIPI?
>>> 
>> Because we don't have IOAPIC/LAPIC...
> 
> Is it necessary to remove the LAPICs completely? If you go very far down the
> route of ripping emulated stuff out of HVM, it starts to feel like starting
> with a pure PV guest and HVMing it up is closer in spirit to what you might
> be aiming for.

The other thing is, removing some of this stuff weakens the argument that
the hybrid approach lets us 'ride the wave' of improving hardware virt
support. For example, LAPIC is pretty architectural these days, and is ripe
for fuller hardware virtualisation. If you put HVM onto event channels and
totally rip out the LAPIC, where does that leave us if full LAPIC virt comes
along, with all its potential for especially improving device passthru
performance?

 -- Keir



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