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    SubjectRe: [NFS] Re: [PATCH] zerocopy NFS for 2.5.36
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    Hello,

    > > > details, but I do know that using copy_from_user() is not a real
    > > > improvement at least on x86 architecture.
    > >
    > > The same as bit is easy to explain. Its totally memory bandwidth limited
    > > on current x86-32 processors. (Although I'd welcome demonstrations to
    > > the contrary on newer toys)
    >
    > Nope. There are distinct alignment problems with movsl-based
    > memcpy on PII and (at least) "Pentium III (Coppermine)", which is
    > tested here:
    ...
    > I have various scriptlets which generate the entire matrix.
    >
    > I think I ended up deciding that we should use movsl _only_
    > when both src and dsc are 8-byte-aligned. And that when you
    > multiply the gain from that by the frequency*size with which
    > funny alignments are used by TCP the net gain was 2% or something.

    Amazing! I beleived 4-byte-aligned was enough.
    read/write systemcalls may also reduce their penalties.

    > It needs redoing. These differences are really big, and this
    > is the kernel's most expensive function.
    >
    > A little project for someone.

    OK, if there is nobody who wants to do it I'll do it by myself.

    > The tools are at http://www.zip.com.au/~/linux/cptimer.tar.gz

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