Re: [Qemu-devel] [PATCH 0/6] in kernel irqchip support

[Glauber Costa]

On Tue, Sep 29, 2009 at 01:39:58AM +0100, Jamie Lokier wrote:
> Glauber Costa wrote:
> >I am ready to advocate that it should be the default, whenever
> >available.  I plan to, however, provide a patch that disables it
> >whenever this gets merged.
> 
> Is the in-kernel irqchip simply intended to accelerate some part of
> the CPU/irq emulation, so that you could enable or disable it at will,
> as well as migrating to TCG-using systems and back, with no observable
> effect except performance?
I don't think we can migrate between kvm and tcg. Although it should be possible
in theory, since we just load the state, there are some differences, specially
with respect to memory layout between kvm and pure tcg. i.e., IIRC, kvm puts two
extra pages in the end of the registered physical memory. Although it can be 
possible,
I don't think anyone has enough interest to make it happen.

As for in-kernel chip, to be honest, I have never tried migrating between two 
system,
one having it, and one lacking it. But I believe it should be possible, and this
is a much easier goal to accomplish.