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



    >> virtio is already non-kvm-specific (lguest uses it) and
    >> non-pci-specific (s390 uses it).
    >>
    >
    > Ok, then to be more specific, I need it to be more generic than it
    > already is. For instance, I need it to be able to integrate with
    > shm_signals.

    Why?



    >> If you have a good exit mitigation scheme you can cut exits by a
    >> factor of 100; so the userspace exit costs are cut by the same
    >> factor. If you have good copyless networking APIs you can cut the
    >> cost of copies to zero (well, to the cost of get_user_pages_fast(),
    >> but a kernel solution needs that too).
    >>
    >
    > "exit mitigation' schemes are for bandwidth, not latency. For latency
    > it all comes down to how fast you can signal in both directions. If
    > someone is going to do a stand-alone request-reply, its generally always
    > going to be at least one hypercall and one rx-interrupt. So your speed
    > will be governed by your signal path, not your buffer bandwidth.
    >

    The userspace path is longer by 2 microseconds (for two additional
    heavyweight exits) and a few syscalls. I don't think that's worthy of
    putting all the code in the kernel.

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



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