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    SubjectRe: [patch 1/13] Qsort
    On Sun, 23 Jan 2005, Andi Kleen wrote:

    > Felipe Alfaro Solana <lkml@mac.com> writes:
    > >
    > > AFAIK, XOR is quite expensive on IA32 when compared to simple MOV
    > > operatings. Also, since the original patch uses 3 MOVs to perform the
    > > swapping, and your version uses 3 XOR operations, I don't see any
    > > gains.
    >
    > Both are one cycle latency for register<->register on all x86 cores
    > I've looked at. What makes you think differently?
    >
    > -Andi (who thinks the glibc qsort is vast overkill for kernel purposes
    > where there are only small data sets and it would be better to use a
    > simpler one optimized for code size)
    >
    How about a shell sort? if the data is mostly sorted shell sort beats
    qsort lots of times, and since the data sets are often small in-kernel,
    shell sorts O(n^2) behaviour won't harm it too much, shell sort is also
    faster if the data is already completely sorted. Shell sort is certainly
    not the simplest algorithm around, but I think (without having done any
    tests) that it would probably do pretty well for in-kernel use... Then
    again, I've known to be wrong :)


    --
    Jesper Juhl

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