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    SubjectWhy is wmb() a no-op on x86_64?
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    Hi, Andi -

    I notice that wmb() is a no-op on x86_64 kernels unless
    CONFIG_UNORDERED_IO is set. Is there any particular reason for this?
    It's not similarly conditional on other platforms, and as a consequence,
    in our driver (which requires a write barrier in some situations for
    correctness), I have to add the following piece of ugliness:

    #if defined(CONFIG_X86_64) && !defined(CONFIG_UNORDERED_IO)
    #define ipath_wmb() asm volatile("sfence" ::: "memory")
    #else
    #define ipath_wmb() wmb()
    #endif

    <b

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