[PATCH] Document Linux's memory barriers [try #2]

[Paul Mackerras]

Linus Torvalds writes:

> > If you ask me, the need for mmiowb on some platforms merely shows that
> > those platforms' implementations of spinlocks and read*/write* are
> > buggy...
> 
> You could also state that same as
> 
> 	"If you ask me, the need for mmiowb on some platforms merely shows 
> 	 that those platforms perform like a bat out of hell, and I think 
> 	 they should be slower"
> 
> because the fact is, x86 memory barrier rules are just about optimal for 
> performance.

... and x86 mmiowb is a no-op.  It's not x86 that I think is buggy.

Paul.