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    SubjectRe: Memory Barrier Definitions
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    > forms of processor memory barrier instructions.  It is _very_ expensive
    > to blindly force all memory references to be ordered completely to the
    > seperate spaces. The use of wmb(), rmb(), and mb() is overloaded in the
    > context of PowerPC.

    I think I follow

    You have

    Compiler ordering
    CPU v CPU memory ordering
    CPU v I/O memory ordering
    I/O v I/O memory ordering

    and our current heirarchy is a little bit more squashed than that. I'd
    agree. We actually hit a corner case of this on the IDT winchip x86 where
    we run relaxed store ordering and have to define wmb() as a locked add of
    zero to the top of stack - which does have a penalty that isnt needed
    for CPU ordering.

    How much of this impacts Mips64 ?

    Alan


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