Re: [Lse-tech] Re: RFC: patch to allow lock-free traversal of lists

[Alan Cox]

> It is discussed in the multi-procesor management section, under "memory
> ordering", and it does say that "reads can be carried out specilatively
> and in any order".
> 
> HOWEVER, it does have what Intel calles "processor order", and it claims
> that "writes by a single processor are observed in the same order by all
> processors."

The other thing on the intel side is that you have to read the errata
documentation. There are an interesting collection of misordering errata.

> (But Intel has redefined the memory ordering so many times that they might
> redefine it in the future too and say that dependent loads are ok. I
> suspect most of the definitions are of the type "Oh, it used to be ok in
> the implementation even though it wasn't defined, and it turns out that
> Windows doesn't work if we change it, so we'll define darkness to be the
> new standard"..)

Its notable that the folks who did looser ordering x86 clones had MTRRs
to enable the performance boost

Alan