Re: [patch 2] mm: speculative get_page

William Lee Irwin III
2005-06-28T14:22:52Z

On Mon, Jun 27, 2005 at 10:08:27PM -0700, David S. Miller wrote:
> BTW, I disagree with this assertion. spin_unlock() does imply a
> memory barrier.
> All memory operations before the release of the lock must execute
> before the lock release memory operation is globally visible.

The affected architectures have only recently changed in this regard.
ppc64 was the most notable case, where it had a barrier for MMIO
(eieio) but not a general memory barrier. PA-RISC likewise formerly had
no such barrier and was a more normal case, with no barrier whatsoever.

Both have since been altered, ppc64 acquiring a heavyweight sync
(arch nomenclature), and PA-RISC acquiring 2 memory barriers.

-- wli