[dpdk-dev] [PATCH] net/virtio: fix wrong TX pkt length stats

[Yang, Zhiyong]

Hi Maxime,

> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin at redhat.com]
> Sent: Friday, October 13, 2017 6:06 PM
> To: Yang, Zhiyong <zhiyong.yang at intel.com>; dev at dpdk.org
> Cc: yliu at fridaylinux.org; Tan, Jianfeng <jianfeng.tan at intel.com>
> Subject: Re: [PATCH] net/virtio: fix wrong TX pkt length stats
> 
> Hi Zhiyong,
> 
> On 10/11/2017 06:39 AM, Zhiyong Yang wrote:
> > In the function virtqueue_enqueue_xmit(), when can_push == 1 is true,
> > vtnet_hdr_size is added to pkt_len by calling rte_pktmbuf_prepend.
> > So, virtio header len should be subtracted before calling stats
> > function.
> >
> > Fixes: 58169a9c8153 ("net/virtio: support Tx checksum offload")
> >
> > Signed-off-by: Zhiyong Yang <zhiyong.yang at intel.com>
> > ---
> >   drivers/net/virtio/virtio_rxtx.c | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/net/virtio/virtio_rxtx.c
> > b/drivers/net/virtio/virtio_rxtx.c
> > index 609b4138a..bf14f9a99 100644
> > --- a/drivers/net/virtio/virtio_rxtx.c
> > +++ b/drivers/net/virtio/virtio_rxtx.c
> > @@ -1079,6 +1079,12 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf
> **tx_pkts, uint16_t nb_pkts)
> >   		/* Enqueue Packet buffers */
> >   		virtqueue_enqueue_xmit(txvq, txm, slots, use_indirect,
> can_push);
> >
> > +		/* In function virtqueue_enqueue_xmit(), when can_push == 1
> > +		 * is true, vtnet_hdr_size is added to pkt_len of mbuf. So, it
> > +		 * should be subtracted before calling stats function.
> > +		 */
> > +		if (can_push == 1)
> > +			txm->pkt_len -= txvq->vq->hw->vtnet_hdr_size;
> >   		txvq->stats.bytes += txm->pkt_len;
> 
> I acknowledge the problem, but I don't like modifying pkt_len.
> This is not the case currently, but in case we want to do something with the
> mbuf later in virtio_xmit_cleanup(), it could be good to have the real length
> there.
> 
> What about:
> 
> if (can_push == 1)
>      txvq->stats.bytes += txm->pkt_len - txvq->vq->hw->vtnet_hdr_size; else
>      txvq->stats.bytes += txm->pkt_len;

I don't like modifying pkt_len, too.
But We need to consider that some stats are updated in virtio_update_packet_stats()
In this function,  pkt_len will be used further.  

Thanks
Zhiyong 

> 
> Thanks,
> Maxime
> 
> >   		virtio_update_packet_stats(&txvq->stats, txm);
> >   	}
> >