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    SubjectRe: [PATCH] Futexes IV (Fast Lightweight Userspace Semaphores)
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    > > It's not just 386 vs later due to cmpxchg. It's also the simple issue of
    > > UP vs SMP - a UP system still wants to do locking, but it doesn't need the
    > > lock prefix. And that lock prefix makes a _huge_ difference
    > > performance-wise.
    >
    > Fail to see why that matters. User level locking is mostly beneficial on SMPs.
    > So, you lock the bus for the atomic update. This is UP, nothing's going on
    > on the bus anyway.

    Lots of older x86 is too stupid to optimise exclusive cache line locked
    operations. After all the bus is still shared - PCI bus masters for one

    Alan
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