On Thu, 6 May 2010 07:30:00 pm Avi Kivity wrote: > On 05/05/2010 11:58 PM, Michael S. Tsirkin wrote: > > + /* We publish the last-seen used index at the end of the available ring. > > + * It is at the end for backwards compatibility. */ > > + vr->last_used_idx =&(vr)->avail->ring[num]; > > + /* Verify that last used index does not spill over the used ring. */ > > + BUG_ON((void *)vr->last_used_idx + > > + sizeof *vr->last_used_idx> (void *)vr->used); > > } > > > > Shouldn't this be on its own cache line?
It's next to the available ring; because that's where the guest publishes its data. That whole page is guest-write, host-read. Putting it on a cacheline by itself would be a slight pessimization; the host cpu would have to get the last_used_idx cacheline and the avail descriptor cacheline every time. This way, they are sometimes the same cacheline. Hope that clarifies, Rusty. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
