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SubjectRe: [BUG] long freezes on thinkpad t60
On Wed, 27 Jun 2007, Linus Torvalds wrote:

> > IOW shouldn't an mfence always be there? Not only loads could leak up
> > into the wait phase, but stores too, if they have no dependency with the
> > "head" and "tail" loads.
>
> Stores never "leak up". They only ever leak down (ie past subsequent loads
> or stores), so you don't need to worry about them. That's actually already
> documented (although not in those terms), and if it wasn't true, then we
> couldn't do the spin unlock with just a regular store anyway.

Yes, Intel has never done that. They'll probably never do it since it'll
break a lot of system software (unless they use a new mode-bit that
allows system software to enable lose-ordering). Although I clearly
remember to have read in one of their P4 optimization manuals to not
assume this in the future.



- Davide


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