On Mon, Oct 19, 2015 at 09:17:18AM +0800, Boqun Feng wrote:
> This is confusing me right now. ;-)
>
> Let's use a simple example for only one primitive, as I understand it,
> if we say a primitive A is "fully ordered", we actually mean:
>
> 1. The memory operations preceding(in program order) A can't be
> reordered after the memory operations following(in PO) A.
>
> and
>
> 2. The memory operation(s) in A can't be reordered before the
> memory operations preceding(in PO) A and after the memory
> operations following(in PO) A.
>
> If we say A is a "full barrier", we actually means:
>
> 1. The memory operations preceding(in program order) A can't be
> reordered after the memory operations following(in PO) A.
>
> and
>
> 2. The memory ordering guarantee in #1 is visible globally.
>
> Is that correct? Or "full barrier" is more strong than I understand,
> i.e. there is a third property of "full barrier":
>
> 3. The memory operation(s) in A can't be reordered before the
> memory operations preceding(in PO) A and after the memory
> operations following(in PO) A.
>
> IOW, is "full barrier" a more strong version of "fully ordered" or not?
Yes, that was how I used it.
Now of course; the big question is do we want to promote this usage or
come up with a different set of words describing this stuff.
I think separating the ordering from the transitivity is useful, for we
can then talk about and specify them independently.
That is, we can say:
LOAD-ACQUIRE: orders LOAD->{LOAD,STORE}
weak transitivity (RCpc)
MB: orders {LOAD,STORE}->{LOAD,STORE} (fully ordered)
strong transitivity (RCsc)
etc..
Also, in the above I used weak and strong transitivity, but that too is
of course up for grabs.
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev
