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    SubjectRe: zero-copy TCP fileserving
    On Thu, 3 Jun 1999, Johannes Erdfelt wrote:

    > > This simple zero-copy isn't really a win on most PC hardware as it takes
    > > about the same amount of time to do a checksum as it does to do a checksum
    > > and copy.
    >
    > What about the new network cards which can do checksums in hardware?

    That's currently a special case. The architecture is optimized for the
    common case and currently compares quite favorably to other systems, even
    those that use zero-copy approaches..

    > > A more powerful scheme is being investigated by sct and a couple others. A
    > > related scheme worked out on FreeBSD and presented at a recent Usenix
    > > could cache checksums, for example.
    >
    > Hmm, caching checksums? I wonder how that would work. It would only work
    > on data which is somewhat repeated. This would probably be a no win for
    > encrypted data. Albeit, I haven't read the paper yet, so I dunno how it
    > works.

    The Linux network stack is much faster than any decent software encryption
    scheme, all of which make a dozen or more read/write rounds on its
    input, so that isn't a very interesting case. The interesting cases for
    networking are file and web serving, and these seem fairly amenable to the
    IO-Lite style approach (even some dynamic content).

    --
    "Love the dolphins," she advised him. "Write by W.A.S.T.E.."


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