Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mon, 20 Aug 2007 22:46:47 -0700 (PDT)

Ie a "barrier()" is likely _cheaper_ than the code generation downside 
from using "volatile".

Assuming GCC were ever better about the code generation badness
with volatile that has been discussed here, I much prefer
we tell GCC "this memory piece changed" rather than "every
piece of memory has changed" which is what the barrier() does.

I happened to have been scanning a lot of assembler lately to
track down a gcc-4.2 miscompilation on sparc64, and the barriers
do hurt quite a bit in some places.  Instead of keeping unrelated
variables around cached in local registers, it reloads everything.