Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code

Trent Piepho
2008-05-20T22:26:47Z

On Tue, 20 May 2008, Benjamin Herrenschmidt wrote:
> On Tue, 2008-05-20 at 16:38 -0500, Scott Wood wrote:
>> It looks like we rely on -fno-strict-aliasing to prevent reordering
>> ordinary memory accesses (such as to DMA descriptors) past the I/O
>> access. It won't prevent reordering of memory reads around an I/O
>> read,
>> though, which could be a problem if the I/O read result determines
>> the
>> validity of the DMA buffer. IMHO, a memory clobber would be better.
>
> We probably want a full "memory" clobber then...

As far as I could tell, no other arch has a full memory clobber. I can see
the argument for changing the Linux model to be stricter and less efficient,
but easier to program for. Not that I entirely agree with it.

But I don't see a good reason for why powerpc should be different than
everything else.