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xen-devel
Re: [Xen-devel] domU to dom0 switch question
On 04/02/2010 07:28 PM, George Valzcig wrote:
I read from the Xen paper dom0 is used for I/O backend driver - you
also explain it - thanks. So if some domU wants to I/O, *and only one
physical CPU*, domU gets unscheduled - dom0 scheduled - yes?
Yes. From Xen's perspective, dom0 is just another domain, so it
schedules all vcpus the same way; if there's contention for pcpus, then
it needs to context switch between multiple vcpus according to its
scheduling algorithm.
My question 1 is, apart from I/O backend driver, is dom0 used for
anything else? I assume application running on domU no I/O. Any other
reason why domU will require the help of dom0.
Not really. Once a domain has started, it is independent of dom0 unless
it specifically makes use of its services. An hvm domain using a stub
domain won't make any direct use of dom0 - all its IO requests will be
proxied via the stub domain.
My question 2 is, domU requests some service (like page table update)
using hypercall. Will this (executing the hypercall and related code)
need dom0?
No. Xen handles all hypercalls directly (though some of them may
involve another domain).
J
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