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    SubjectRe: page table lock patch V15 [0/7]: overview
    On Fri, Jan 14, 2005 at 04:39:16AM +0100, Roman Zippel wrote:
    > Hi,
    >
    > Christoph Lameter wrote:
    >
    > >Introduction of the cmpxchg is one atomic operations that replaces the two
    > >spinlock ops typically necessary in an unpatched kernel. Obtaining the
    > >spinlock requires an spinlock (which is an atomic operation) and then the
    > >release involves a barrier. So there is a net win for all SMP cases as far
    > >as I can see.
    >
    > But there might be a loss in the UP case. Spinlocks are optimized away,
    > but your cmpxchg emulation enables/disables interrupts with every access.

    Only for 386s and STI/CLI is quite cheap there.

    -Andi
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