Re: I/O write ordering

Benjamin Herrenschmidt
2004-09-22T14:44:32Z

On Thu, 2004-09-23 at 00:32, Matthew Wilcox wrote:

> I'd quite like to hear opinions from the PPC and Alpha people, they seem to
> be the most out-of-order architectures.

The more specific the barrier is, the happier we are on ppc so we can
select the right one in our collection :)

Write ordering is usually just a matter of eieio. _however_ the main
problem we have is write ordering between two different storage classes,
that is between cacheable space and non cacheable space. Our normal
write ordering barrier will not order between those, thus causing all
sorts of issues with devices mixing MMIO & DMA. We have to use a more
heavy-weight barrier in those cases, but currently, linux lacks the
proper abstraction for that, thus we had to clutter then normal MMIO
writes to do the big barrier each time to be safe ...

Ben.