On Wed, Jan 27, 2010 at 11:46:32AM +0200, Avi Kivity wrote: > On 01/27/2010 11:36 AM, Michael S. Tsirkin wrote: >> >> >>> smp_mb() is used for processor-vs-processor ordering, which can't happen >>> on UP systems, but for process-vs-device, we must use mb(). >>> >>> (this shows up if running a UP guest on an SMP host). >>> >> Currently, yes. But virtio is not a real device. >> Here's what I was really trying to improve: rmb() is an lfence on >> x86_64, but smp_rmb() is a barrier() and this is really sufficient for >> virtio because x86_64 does not reorder memory reads. >> >> > > x86_64 can do speculative and reordered reads. Intel system programming says: 7.2.3.2 Neither Loads Nor Stores Are Reordered with Like Operations Doesn't this mean that reads are not reordered? If no what does it mean? >> Does this mean such an optimization would need a new macro? >> > > Please no. > > -- > Do not meddle in the internals of kernels, for they are subtle and quick to panic. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
