Messages in this thread | | | Date | Wed, 22 Mar 2006 09:27:11 -0800 | From | Chris Wright <> | Subject | Re: [RFC PATCH 00/35] Xen i386 paravirtualization support |
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* Anthony Liguori (aliguori@us.ibm.com) wrote: > Chris Wright wrote: > >Xen also provides support for running directly on native hardware. > > Can someone elaborate on this? Does this mean a Xen guest can run on > bare metal?
Yes. See the Xen code for running the kernel in ring0 with Xen (supervisor_mode_kenel). The hypercall_page is conditionally filled with hypercall traps or direct calls basically.
> Is there code available to make this work (it doesn't seem contained in > this patchset)? Has any performance analysis been done?
I don't have any numbers.
> The numbers that have been posted with the VMI patches suggest that some > rather tricky stuff is required to achieve native performance when > running a guest on bare metal. If this is not the case, it would be > very interesting to know because it seems to be the hairiest part of the > VMI patches.
It is a hairy part of VMI. They've done a nice job of handling the native case, and have interseting plans for improving the non-native case (inline where possible). One of the differences is things that don't actually require hypercalls are already inline w/ Xen. So it's conceivable that the performance hit is smaller than what VMI found without carefully inlining native code.
> Otherwise, if we want to support Xen guests on bare metal, it seems we > would have to change things in the subarch code a bit to do something > similar to VMI.
It's a different approach.
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