Re: [PATCH v2 1/7] vhost: refactor rte_vhost_dequeue_burst

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Thu, Mar 03, 2016 at 05:40:14PM +0000, Xie, Huawei wrote:
> On 2/18/2016 9:48 PM, Yuanhan Liu wrote:
> > The current rte_vhost_dequeue_burst() implementation is a bit messy
> [...]
> > +
> >  uint16_t
> >  rte_vhost_dequeue_burst(struct virtio_net *dev, uint16_t queue_id,
> >  	struct rte_mempool *mbuf_pool, struct rte_mbuf **pkts, uint16_t count)
> >  {
> > -	struct rte_mbuf *m, *prev;
> >  	struct vhost_virtqueue *vq;
> > -	struct vring_desc *desc;
> > -	uint64_t vb_addr = 0;
> > -	uint64_t vb_net_hdr_addr = 0;
> > -	uint32_t head[MAX_PKT_BURST];
> > +	uint32_t desc_indexes[MAX_PKT_BURST];
> 
> indices

http://dictionary.reference.com/browse/index

    index
    noun, plural indexes, indices 

> 
> 
> >  	uint32_t used_idx;
> >  	uint32_t i;
> > -	uint16_t free_entries, entry_success = 0;
> > +	uint16_t free_entries;
> >  	uint16_t avail_idx;
> > -	struct virtio_net_hdr *hdr = NULL;
> > +	struct rte_mbuf *m;
> >  
> >  	if (unlikely(!is_valid_virt_queue_idx(queue_id, 1, dev->virt_qp_nb))) {
> >  		RTE_LOG(ERR, VHOST_DATA,
> > @@ -730,197 +813,49 @@ rte_vhost_dequeue_burst(struct virtio_net *dev, uint16_t queue_id,
> >  		return 0;
> >  
> > -		if (entry_success < (free_entries - 1)) {
> > -			/* Prefetch descriptor index. */
> > -			rte_prefetch0(&vq->desc[head[entry_success+1]]);
> > -			rte_prefetch0(&vq->used->ring[(used_idx + 1) & (vq->size - 1)]);
> > -		}
> 
> Why is this prefetch silently dropped in the patch?

Oops, good catching. Will fix it. Thanks.


> >  			break;
> > +		pkts[i] = m;
> >  
> > -		m->nb_segs = seg_num;
> > -		if ((hdr->flags != 0) || (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE))
> > -			vhost_dequeue_offload(hdr, m);
> > -
> > -		pkts[entry_success] = m;
> > -		vq->last_used_idx++;
> > -		entry_success++;
> > +		used_idx = vq->last_used_idx++ & (vq->size - 1);
> > +		vq->used->ring[used_idx].id  = desc_indexes[i];
> > +		vq->used->ring[used_idx].len = 0;
> 
> What is the correct value for ring[used_idx].len,  the packet length or 0?

Good question. I didn't notice that before. Sounds buggy to me. However,
that's from the old code. Will check it.

	--yliu