Re: [SeaBIOS] [PATCH] virtio: clean up memory barrier usage

[Gleb Natapov]

On Thu, May 20, 2010 at 04:36:32PM +0300, Michael S. Tsirkin wrote:
> diff --git a/src/virtio-ring.h b/src/virtio-ring.h
> index 3fb86fe..8b546f4 100644
> --- a/src/virtio-ring.h
> +++ b/src/virtio-ring.h
> @@ -9,8 +9,9 @@
>
> #define virt_to_phys(v) (unsigned long)(v)
>  #define phys_to_virt(p) (void*)(p)
> -#define wmb() barrier()
> -#define mb() barrier()
> +/* Compiler barrier is enough as an x86 CPU does not reorder reads or writes */
> +#define smp_rmb() barrier()
> +#define smp_wmb() barrier()

I thought you were going to use real memory barriers (although we
concluded compiler barrier should be enough, but it's better to be safe
then sorry).