Re: [dpdk-stable] [PATCH v2] net/virtio: fix wrong TX pkt length stats

["Yang, Zhiyong" <zhiyong.yang@intel.com>]

Yuanhan,

> -----Original Message-----
> From: Yuanhan Liu [mailto:yliu@fridaylinux.org]
> Sent: Monday, October 23, 2017 9:22 PM
> To: Yang, Zhiyong <zhiyong.yang@intel.com>
> Cc: dev@dpdk.org; stable@dpdk.org; maxime.coquelin@redhat.com
> Subject: Re: [PATCH v2] net/virtio: fix wrong TX pkt length stats
> 
> On Mon, Oct 23, 2017 at 02:40:36PM +0800, Zhiyong Yang wrote:
> > In the function virtqueue_enqueue_xmit(), when can_push is true,
> > vtnet_hdr_size is added to pkt_len by calling rte_pktmbuf_prepend.
> > So, virtio header length should be subtracted before calling stats
> > function.
> >
> > Fixes: 58169a9c8153 ("net/virtio: support Tx checksum offload")
> >
> > Cc: stable@dpdk.org
> > Cc: yliu@fridaylinux.org
> > Cc: maxime.coquelin@redhat.com
> > Signed-off-by: Zhiyong Yang <zhiyong.yang@intel.com>
> > Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> > ---
> >
> > Changes in V2:
> > Put code in the function virtqueue_enqueue_xmit() according to
> > yuanhan's comments.
> >
> >  drivers/net/virtio/virtio_rxtx.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/net/virtio/virtio_rxtx.c
> > b/drivers/net/virtio/virtio_rxtx.c
> > index 2cf82fef4..f28751e07 100644
> > --- a/drivers/net/virtio/virtio_rxtx.c
> > +++ b/drivers/net/virtio/virtio_rxtx.c
> > @@ -396,6 +396,13 @@ virtqueue_enqueue_xmit(struct virtnet_tx *txvq,
> struct rte_mbuf *cookie,
> >  		vq->vq_desc_tail_idx = idx;
> >  	vq->vq_free_cnt = (uint16_t)(vq->vq_free_cnt - needed);
> >  	vq_update_avail_ring(vq, head_idx);
> > +
> > +	/* when can_push is true, vtnet_hdr_size is added to pkt_len
> > +	 * of mbuf. It should be subtracted in order to make stats function
> > +	 * work in the right way.
> > +	 */
> > +	if (can_push)
> > +		cookie->pkt_len -= head_size;
> 
> I actually meant to put it inside the "if (can_push)" clause, so that you don't have
> to add yet another if. The another reason I wanted you to do the move is,
> rte_pktmbuf_prepend (which did the magic) is exactly invoked inside this if. Such
> move puts logical related code tight together. At least, you could make the
> comment simpler: you don't have to say "when can_push is true ...". Instead, it
> could be:
> 
>     /*
>      * rte_pktmbuf_prepend() counts the hdr size to the pkt length,
>      * which is wrong. Below subtract restores the correct pkt size.
>      */
> 
> 	--yliu

You are right.  I mistakenly think that cookie->pkt_len will be used to transmit pkts .
Actually cookie->data_len will is used when filling the descriptors.
No problem. V3 will be sent soon.

Zhiyong