CMPXCHG - all or nothing

By: Michael S (, March 20, 2008 6:38 am
Room: Moderated Discussions
Linus Torvalds ( on 3/19/08 wrote:
>Also, the x86 memory model is not a machine-wide
>complete ordering - the memory model is called "processor
>ordering", and it means that each CPU sees the stores of
>other individual CPU's in a well-defined order.
>See the Intel memory ordering whitepaper for all the gritty
>details (just google for that phrase, the first hit will
>be it).

I did read Intel memory ordering whitepaper before posting the original post. It clearly states that locked operations from different agents are ordered in absolute machine-wide order (i.e. seen in the same order by all observers) rather than in "processor order" like the rest of the WB stores.
I'm too stupid to figure out whether semantics like these constrain possible implementations of big hierarchical directory based NUMA machines.
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