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    SubjectRe: splice/vmsplice performance test results
    From
    From: Jens Axboe <jens.axboe@oracle.com>
    Date: Thu, 16 Nov 2006 22:21:07 +0100

    > On Thu, Nov 16 2006, David Miller wrote:
    > > From: "Jim Schutt" <jaschut@sandia.gov>
    > > Date: Thu, 16 Nov 2006 11:08:59 -0700
    > >
    > > > Or is read+write really the fastest way to get data off a
    > > > socket and into a file?
    > >
    > > There is still no explicit TCP support for splice/vmsplice so things
    > > get copied around and most of the other advantaves of splice/vmplice
    > > aren't obtained either. So perhaps that explains your numbers.
    >
    > There should not be any copying for tcp send, at least no more than what
    > sendfile() did/does. Hmm?

    That's true on send, correct.

    > > Jens Axboe tries to get things working, and others have looked into it
    > > too, but adding TCP support is hard and for several reasons folks like
    > > Alexey Kuznetsov and Evgeniy Polyakov believe that sys_receivefile()
    > > is an interface much better suited for TCP receive.
    > >
    > > splice/vmsplice has a lot of state connected to a transaction, and
    > > perhaps that is part of why Evgeniy and Alexey have trouble wrapping
    > > their brains around an efficient implementation.
    >
    > I hope to try and see if I can help get some of that done, however I
    > need all the help I can get on the networking side. Not sure I
    > understand why it has to be so difficult, if we need to define a wrapper
    > container instead of passing down a pipe that is completely fine with
    > me. The networking code basically just needs to hang on to the
    > pipe_buffer and release it on ack for send, receive is somewhat more
    > involved (and I don't know enough about networking to voice any
    > half-intelligent opinion on that!).
    >
    > I would just consider it a damn shame if we cannot complete the splice
    > family and need to punt to something else for net receive.

    I'm sure that the folks on netdev@vger.kernel.org are more than
    willing to give you a hand in this area :-)
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