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    SubjectRe: [PATCH v3 3/6] vbus: add a "vbus-proxy" bus model for vbus_driver objects

    * Anthony Liguori <anthony@codemonkey.ws> wrote:

    > Ingo Molnar wrote:
    >> * Gregory Haskins <ghaskins@novell.com> wrote:
    >>
    >>
    >>> This will generally be used for hypervisors to publish any host-side
    >>> virtual devices up to a guest. The guest will have the opportunity
    >>> to consume any devices present on the vbus-proxy as if they were
    >>> platform devices, similar to existing buses like PCI.
    >>>
    >>> Signed-off-by: Gregory Haskins <ghaskins@novell.com>
    >>> ---
    >>>
    >>> MAINTAINERS | 6 ++
    >>> arch/x86/Kconfig | 2 +
    >>> drivers/Makefile | 1 drivers/vbus/Kconfig |
    >>> 14 ++++
    >>> drivers/vbus/Makefile | 3 +
    >>> drivers/vbus/bus-proxy.c | 152 +++++++++++++++++++++++++++++++++++++++++++
    >>> include/linux/vbus_driver.h | 73 +++++++++++++++++++++
    >>> 7 files changed, 251 insertions(+), 0 deletions(-)
    >>> create mode 100644 drivers/vbus/Kconfig
    >>> create mode 100644 drivers/vbus/Makefile
    >>> create mode 100644 drivers/vbus/bus-proxy.c
    >>> create mode 100644 include/linux/vbus_driver.h
    >>>
    >>
    >> Is there a consensus on this with the KVM folks? (i've added the KVM
    >> list to the Cc:)
    >
    > I'll let Avi comment about it from a KVM perspective but from a
    > QEMU perspective, I don't think we want to support two paravirtual
    > IO frameworks. I'd like to see them converge. Since there's an
    > install base of guests today with virtio drivers, there really
    > ought to be a compelling reason to change the virtio ABI in a
    > non-backwards compatible way. This means convergence really ought
    > to be adding features to virtio.

    I agree.

    While different paravirt drivers are inevitable for things that are
    externally constrained (say support different hypervisors), doing
    different _Linux internal_ paravirt drivers looks plain stupid and
    counter-productive. It splits testing and development.

    So either the vbus code replaces virtio (for technical merits such
    as performance and other details), or virtio is enhanced with the
    vbus performance enhancements.

    > On paper, I don't think vbus really has any features over virtio.
    > vbus does things in different ways (paravirtual bus vs. pci for
    > discovery) but I think we're happy with how virtio does things
    > today.
    >
    > I think the reason vbus gets better performance for networking
    > today is that vbus' backends are in the kernel while virtio's
    > backends are currently in userspace. Since Michael has a
    > functioning in-kernel backend for virtio-net now, I suspect we're
    > weeks (maybe days) away from performance results. My expectation
    > is that vhost + virtio-net will be as good as venet + vbus. If
    > that's the case, then I don't see any reason to adopt vbus unless
    > Greg things there are other compelling features over virtio.

    Keeping virtio's backend in user-space was rather stupid IMHO.

    Having the _option_ to piggyback to user-space (for flexibility,
    extensibility, etc.) is OK, but not having kernel acceleration is
    bad.

    Ingo


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