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    SubjectRe: Why Semaphore Hardware-Dependent?
    On Sun, 27 Aug 2006, Chris Wedgwood wrote:

    > On Mon, Aug 28, 2006 at 10:18:35AM +1000, Paul Mackerras wrote:
    >
    > > I believe the reason for not doing something like this on x86 was
    > > the fact that we still support i386 processors, which don't have the
    > > cmpxchg instruction. That's fair enough, but I would be opposed to
    > > making semaphores bigger and slower on PowerPC because of that.
    > > Hence the two different styles of implementation.
    >
    > The i386 is older than some of the kernel hackers, and given that a
    > modern kernel is pretty painful with less than say 16MB or RAM in
    > practice, I don't see that it would be all that terrible to drop
    > support for ancient CPUs at some point (yes, I know some newer
    > embedded (and similar) CPUs might be affected here too, but surely not
    > that many that people really use --- and they could just use 2.4.x).

    Also note that i386 has a cmpxchg emulation for those machines that do not
    support cmpxchg.

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