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    SubjectRe: [RFC PATCH 00/17] virtual-bus
    Gregory Haskins wrote:



    >> There is no choice. Exiting from the guest to the kernel to userspace
    >> is prohibitively expensive, you can't do that on every packet.
    >>
    >>
    >
    > Now you are making my point ;) This is part of the cost of your
    > signaling path, and it directly adds to your latency time.

    It adds a microsecond. The kvm overhead of putting things in userspace
    is low enough, I don't know why people keep mentioning it. The problem
    is the kernel/user networking interfaces.

    > You can't
    > buffer packets here if the guest is only going to send one and wait for
    > a response and expect that to perform well. And this is precisely what
    > drove me to look at avoiding going back to userspace in the first place.
    >

    We're not buffering any packets. What we lack is a way to tell the
    guest that we're done processing all packets in the ring (IOW, re-enable
    notifications).

    --
    error compiling committee.c: too many arguments to function



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