Re: [patch] linux 2.4.17: The second mb() rework (final)

[Ralf Baechle <ralf@oss.sgi.com>]

On Fri, Feb 15, 2002 at 09:30:45AM +0100, Kevin D. Kissell wrote:

> That is, I would say, a bug in the TX39 implementation of SYNC.
> The specification is states that all stores prior to the SYNC must 
> complete before any memory ops after the sync, and that the 
> definition of a store completing is that all stored values be 
> "visible to every other processor in the system", which pretty 
> clearly implies that the write buffers must be flushed.

In practice sync just isn't good enough.  Most systems these days use
an I/O bus like PCI which uses posted writes or have some other
non-strongly ordered memory model.  Which is why something wmb() or
mb() aren't good enough in driver.  I'm just having a nice discussion
about this topic with SGI's IA64 people; we have to come up with a
portable and efficient ABI.

  Ralf