[openib-general] Re: [PATCH][16/26] IB/mthca: mem-free doorbell record writing

[Jeff Garzik]

Roland Dreier wrote:
>     Jeff> Are you concerned about ordering, or write-combining?
> 
> ordering... write combining would be fine.
> 
>     Jeff> I am unaware of a situation where writes are re-ordered into
>     Jeff> a reversed, descending order for no apparent reason.
> 
> Hmm... I've seen ppc64 do some pretty freaky reordering but on the
> other hand that's a 64-bit arch so we don't care in this case.  I
> guess I'd rather keep the barrier there so we don't have the
> possibility of a rare hardware crash when the HCA just happens to read
> the doorbell record in a corrupt state.

Well, we don't just add code to "hope and pray" for an event that nobody 
is sure can even occur...

Does someone have a concrete case where this could happen?  ever?

	Jeff