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    SubjectRe: [RFC PATCH 00/35] Xen i386 paravirtualization support
    * 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.

    thanks,
    -chris
    -
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