On 11 Jan 2006, at 22:49, Magenheimer, Dan (HP Labs Fort Collins) wrote:
Extra
context switches are added for any page related operation.
Hmmm... not really. Page operations (such as alloc and free)
are relatively rare and can be batched (e.g. at domain startup).
And domU's are not going to be making policy decisions...
If dom0 is making policy decisions (e.g. this stick of RAM is
about to die, who do I steal memory from?), dom0 ownership
of the pages may even reduce context switches.
In a literal/extreme form of your model, any address space
access/update would need to be translated and/or validated by domain0.
That's certainly going to be a significant overhead. I believe that
there is a balance to be struck between sufficient mechanism in Xen to
ensure good performance while allowing flexible policy expression in
the control plane. I think talking about this at the summit would be
very interesting -- are your ideas solidified enough perhaps even for a
short presentation?
-- Keir
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