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    SubjectRe: [PATCH] 2.6 workaround for Athlon/Opteron prefetch errata


    Chris Meadors wrote:

    >On Mon, 2003-09-15 at 08:38, Nick Piggin wrote:
    >
    >
    >>OK, the reason why I don't like the sound of this is because the size
    >>of your option set has now been squared, and its no longer "make these
    >>CPUs work".
    >>
    >
    >The way I see the config option working is, having a sub-menu that says
    >something like, "Select the CPU the kernel will be run on." From there
    >you can pick one CPU. This sets the in kernel optimizations for that
    >CPU, along with the work arounds (obviously). It also sets the compiler
    >flags for the padding, and "-march=[CPU]". Then in a sub-menu of this
    >menu, there is an "Advanced processor selection". The help text would
    >be something like, "In addition to the primary processor selected above,
    >also allow this kernel to be booted on the processors selected below.
    >Selecting this option disables some of the optimizations for the primary
    >processor." Just turning on that option would change the "-march=" to
    >"-mcpu=". Then in the menu one could select from any of the CPUs
    >listed. Each one would enable the work around code to allow the built
    >kernel to run correctly on a machine with a different CPU.
    >
    >I see this as sort of like the advanced partition selection, or the
    >compiled in fonts.
    >

    Look at the complexity though!

    >
    >>I can see an argument for cache line size but thats about it. I can't
    >>think of my optimisations that should be done on one architecture but
    >>not another.
    >>
    >
    >Don't forget the compiler optimization flags. A kernel built with
    >"-march" may not run on any other CPUs.
    >

    Yeah, I really meant _should_, not must. In other words, something that
    is an optimisation for one architecutre, but a pessimisation for
    another.

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