On Mon, Mar 30, 2015 at 10:17:06AM +0200, Paolo Bonzini wrote:
> 
> 
> On 19/03/2015 10:33, Dr. David Alan Gilbert wrote:
> >> > But still pointless.  Atomicity isn't magic pixie dust; it only makes
> >> > sense if you're making atomic specific operations that need to be.
> >> > Simple integer loads and stores are already atomic.  Unless at least
> >> > some of the atomic operations are something more complex, there's
> >> > really no point to atomically marked operations.
> > OK, I'll kill it off.
> 
> No, don't.
> 
> And both of you, read docs/atomics.txt.

*reads*

> "atomic_read() and atomic_set() prevents the compiler from using
> optimizations that might otherwise optimize accesses out of existence
> on the one hand, or that might create unsolicited accesses on the other.
> [...] it tells readers which variables are shared with
> other threads, and which are local to the current thread or protected
> by other, more mundane means."
> 
> atomic_read() and atomic_set() provide the same guarantees as
> ACCESS_ONCE in the Linux kernel.

Ok, having better understood the semantics and intentions of the
atomic_* functions in qemu, I withdraw my objection.  They do seem
like the right primitives for this situation.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson