Re: [Qemu-devel] [PATCH] virtio: Make memory barriers be memory barriers

[Paolo Bonzini]

On 09/01/2011 09:37 AM, Sasha Levin wrote:
> > >  -#define wmb() __asm__ __volatile__("": : :"memory")
> > >  + /* TODO: we may also need rmb()s.  It hasn't bitten us yet, but.. */
> > >  + #define wmb() __sync_synchronize()
>
> That asm directive also implicitly provided a compiler barrier, I could
                     ^^^^

only

> find whether __sync_synchronize() provides one as well.
>
> Any idea if it does?

Of course, __sync_synchronize() is a stronger barrier.  The asm is 
simply not a synchronization primitive.

Paolo