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xen-devel
Re: [Xen-devel] Re: VT-X processors , xen 3.0 , drives and virtualizatio
Ian Brown wrote:
Hello,
Ok, Thnks,this clears a lot about the first question.
Still, I will be grateful if I get any feedback on the second question
: performance overhead of running more than one Linux OS instance on
these VT-processors :
did anybody tried it and can comment on it / give some data / compare to
non VT processors
(which have aboutb 3% performance overhead) ? I would expect that
somebody had tried using these
VT chips (even they are still (maybe) in beta stage ).
VT support in Xen 3.0 is still mostly proof-of-concept. It's not really
fair to use it to analyze the performance of VT since there hasn't been
a lot (although there has been some) performance work done on VT.
The Xen VT support takes a pretty bad performance hit because of the
fact that the device model is run in a different domain so there's a
pretty big hit from world/context switches.
Stay tuned though, because there's no reason why future versions of Xen
shouldn't perform quite well under VT :-)
Regards,
Anthony Liguori
Regards,
IB
On 12/27/05, Charles Duffy <cduffy@xxxxxxxxxxx> wrote:
Ian Brown wrote:
1) True to now and the current xen-3.0 version: When running Xen 3.0
on these VT processors, can we run an unmodified kernel ?
For your DomUs, yes. For your Dom0, no. Running a modified DomU kernel
should be more performant.
and in such a case, what about the device drivers - isn't there a
problem with them ?
Emulated hardware, based off of drivers borrowed from QEMU, is provided
to VMX domains. The drivers they need will be for the emulated cards,
not for the real devices in the machine.
I mean , in practical terms , if I will set my bootloader to have the
following entry on a machine with VT-x processor:
kernel /xen.gz dom0_mem=x
module /vmlinuz-#version ro root=...
(and initrd if needed)
No, that won't work, because that's trying to use an unmodified kernel
as Dom0.
will I be
able to create a new domain based also on unmodified vmlinuz-#version
kernel ?
Yes, though VMX domains work a bit differently from non-VMX ones -- the
process won't be exactly the same except with a non-Xen-enabled kernel.
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