On 24/07/2015 21:36, Michael S. Tsirkin wrote: >On Thu, Aug 27, 2015 at 01:18:47AM +0000, Wang, Wei W wrote: > Hi all, > > > > I have a question about the vring_avail: > > It only includes an idx (equivalent to the ring tail), which is used > by the frontend (virtio_net) to fill bufs. The backend (e.g. > vhost_net) maintains the ring head (last_avail_idx) by itself. The > frontend checks if the ring is full or empty via a counter (vq->num_free). > > My question is why can’t we include the ring head in the vring_avail > struct, so that the vq->num_free is not needed, and the backend can > directly use it without maintaining its own copy? > > > > Thanks, > > Wei > > > >I'm not sure I understand your proposal, and what it would accomplish. Write a >patch, that'll make it easier to discuss. >Also copy all relevant mailing lists, not just kvm.
Thanks Michael. I haven’t got the patch ready yet. I am just wondering if it is better to have "last_avail_idx" in vhost_virtqueue moved into vring_avail. In other regular ring operations, we usually use *head and *tail to judge if the ring is full or empty, but it seems vring_avail does not use this method in virtio_net.c (it uses a counter). Best, Wei
