Re: [PATCH] make atomic_t volatile on all architectures

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Wed, Aug 08, 2007 at 06:48:24PM -0700, David Miller wrote:
> From: Herbert Xu <herbert@gondor.apana.org.au>
> Date: Thu, 09 Aug 2007 09:03:27 +0800
> 
> > Such loops should always use something like cpu_relax() which comes
> > with a barrier.
> 
> This is an excellent point.
> 
> And it needs to be weighed with the error prone'ness Andrew mentioned.
> There probably is a middle ground somewhere.

OK...  I'll bite.  ACCESS_ONCE(), see http://lkml.org/lkml/2007/7/11/664.

This would allow ACCESS_ONCE(atomic_read(&x)) to be used where refetching
would be problematic, but allow the compiler free rein in cases where
refetching is OK.

The ACCESS_ONCE() primitive of course has its limitations as well, but
you did ask for a middle ground.  ;-)

							Thanx, Paul
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/