Messages in this thread | | | Subject | Re: page table lock patch V15 [0/7]: overview II | From | Andi Kleen <> | Date | Fri, 14 Jan 2005 05:52:18 +0100 |
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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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