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    SubjectRe: page table lock patch V15 [0/7]: overview II
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    Andi Kleen <ak@muc.de> writes:
    > As you can see cmpxchg is slightly faster for the cache hot case,
    > but incredibly slow for cache cold (probably because it does something
    > nasty on the bus). This is pretty consistent to Intel and AMD CPUs.
    > Given that page tables are likely more often cache cold than hot
    > I would use the lazy variant.

    Sorry, my benchmark program actually had a bug (first loop included
    page faults). Here are updated numbers. They are somewhat different:

    Athlon 64:
    readpte hot 25
    readpte cold 171
    readpte_cmp hot 18
    readpte_cmp cold 162

    Nocona:
    readpte hot 118
    readpte cold 443
    readpte_cmp hot 22
    readpte_cmp cold 224

    The difference is much smaller here. Assuming cache cold cmpxchg8b is
    better, at least on the Intel CPUs which have a slow rmb().

    -Andi

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