Re: membar_enter semantics

[Joerg Sonnenberger <joerg%bec.de@localhost>]

Am Mon, Feb 14, 2022 at 02:45:46AM +0000 schrieb David Holland:
> On Mon, Feb 14, 2022 at 03:12:29AM +0100, Joerg Sonnenberger wrote:
>  > Am Mon, Feb 14, 2022 at 02:01:13AM +0000 schrieb David Holland:
>  > > In this case I would argue that the names should be membar_load_any()
>  > > and membar_any_store().
>  > 
>  > Kind of like with the BUSDMA_* flags, it is not clear from that name in
>  > which direction they work either. As in: is it a barrier that stops the
>  > next load? Is it a barrier that ensures that a store is visible?
> 
> Given that English is left-to-right, and that memory barriers are
> about ordering memory operations, it seems a lot clearer than "enter".

I don't think that arguments works with the way barriers around read and
write operations are normally used. A read barrier is normally "ensure
that a read doesn't move before this point", where as write barrier is
normally "ensure that a write operation doesn't move beyond this point".
Note the opposite temporal direction. Not sure if there are sensible use
cases of the inverted directions, i.e. if we care about CPUs that can
reorder reads relative to later writes.

Joerg