How expensive is LFENCE?

How expensive is LFENCE?

I'm guessing the new disambiguated memory stuff will
break dependent load ordering. If so, what will be
the effect on some of the scalability techniques that
use dependent load ordering if they have to start
using LFENCE on all dependent loads?

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I'm thinking this won't have any effect on dependent loads
since in effect the pipeline is going to stall anyway until
the load has completed. Is that basically right? I only
have a P3 so I can't test it out for now.

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