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  • Russell King's avatar
    Documentation/volatile-considered-harmful.txt: correct cpu_relax() documentation · 091e635e
    Russell King authored
    cpu_relax() is documented in volatile-considered-harmful.txt to be a
    memory barrier.  However, everyone with the exception of Blackfin and
    possibly ia64 defines cpu_relax() to be a compiler barrier.
    
    Make the documentation reflect the general concensus.
    
    Linus sayeth:
    
    : I don't think it was ever the intention that it would be seen as anything
    : but a compiler barrier, although it is obviously implied that it might
    : well perform some per-architecture actions that have "memory barrier-like"
    : semantics.
    :
    : After all, the whole and only point of the "cpu_relax()" thing is to tell
    : the CPU that we're busy-looping on some event.
    :
    : And that "event" might be (and often is) about reading the same memory
    : location over and over until it changes to what we want it to be.  So it's
    : quite possible that on various architectures the "cpu_relax()" could be
    : about making sure that such a tight loop on loads doesn't starve cache
    : tr...
    091e635e