Re: [dpdk-dev] [PATCH v2] net/virtio: fix an incorrect behavior of device stop/start

["Fischetti, Antonio" <antonio.fischetti@intel.com>]

Hi Tiwei,

I'm doing some regression tests with v17.11-rc4. I ran 
into a hitch with testpmd running into a guest VM. It happens 
that no packet gets forwarded by testpmd.
The issue seems to appear after this patch was upstreamed.

I saw there's a way to make it work, ie by avoiding to 
increment the last consumed descriptor:

--- a/drivers/net/virtio/virtqueue.c
+++ b/drivers/net/virtio/virtqueue.c
@@ -80,7 +80,7 @@ virtqueue_flush(struct virtqueue *vq)
                        rte_pktmbuf_free(dxp->cookie);
                        dxp->cookie = NULL;
                }
-               vq->vq_used_cons_idx++;
+               //vq->vq_used_cons_idx++;
                vq_ring_free_chain(vq, desc_idx);

Not quite sure if this change make any sense to you?

Some details below.

The issue appears only if the traffic generator is already 
sending packets before I launch testpmd in the guest.

In my testbench I have Open-vSwitch (OvS-DPDK) which launches 
a VM with 2 vhostuserclient ports (vhu0 and vhu1), each with 
a single queue.
My OvS has 2 physical ports: dpdk0 and dpdk1.
dpdk0 forwards packets back and forth from/to the generator
to/from vhu0.
Similarly, dpdk1 forwards packets back and forth from/to the generator
to/from vhu1.

In OvS there are 2 different PMD threads serving the 2 
vhostuserclient ports.

While the traffic generator is already sending packets, in the 
guest VM I launch 
  ./testpmd -c 0x3 -n 4 --socket-mem 512 -- --burst=64 -i --txqflags=0xf00 --disable-hw-vlan

The issue is that I see no packet received on the traffic generator 
and in fact testpmd shows

---------------------- Forward statistics for port 0  ----------------------
  RX-packets: 0              RX-dropped: 0             RX-total: 0
  TX-packets: 0              TX-dropped: 0             TX-total: 0
  ----------------------------------------------------------------------------

  ---------------------- Forward statistics for port 1  ----------------------
  RX-packets: 0              RX-dropped: 0             RX-total: 0
  TX-packets: 0              TX-dropped: 0             TX-total: 0
  ----------------------------------------------------------------------------

  +++++++++++++++ Accumulated forward statistics for all ports+++++++++++++++
  RX-packets: 0              RX-dropped: 0             RX-total: 0
  TX-packets: 0              TX-dropped: 0             TX-total: 0
  ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Please let me know if I missed something or if you need 
more info on my testbench.


Thanks,
Antonio

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Tiwei Bie
> Sent: Friday, October 20, 2017 3:09 AM
> To: dev@dpdk.org
> Cc: yliu@fridaylinux.org; maxime.coquelin@redhat.com;
> jfreimann@redhat.com; stable@dpdk.org
> Subject: [dpdk-dev] [PATCH v2] net/virtio: fix an incorrect behavior of
> device stop/start
> 
> After starting a device, the driver shouldn't deliver the
> packets that already existed before the device is started
> to applications. Otherwise it will lead to incorrect packet
> collection for port state. This patch fixes this issue by
> flushing the Rx queues when starting the device.
> 
> Fixes: a85786dc816f ("virtio: fix states handling during
> initialization")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> Reviewed-by: Jens Freimann <jfreimann@redhat.com>
> ---
> v2:
> - Use the existing `for` loop
> - Improve the commit log
> 
>  drivers/net/virtio/virtio_ethdev.c |  2 ++
>  drivers/net/virtio/virtio_rxtx.c   |  2 +-
>  drivers/net/virtio/virtqueue.c     | 25 +++++++++++++++++++++++++
>  drivers/net/virtio/virtqueue.h     |  5 +++++
>  4 files changed, 33 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio/virtio_ethdev.c
> b/drivers/net/virtio/virtio_ethdev.c
> index 42c2836..9ccb0f4 100644
> --- a/drivers/net/virtio/virtio_ethdev.c
> +++ b/drivers/net/virtio/virtio_ethdev.c
> @@ -1819,6 +1819,8 @@ virtio_dev_start(struct rte_eth_dev *dev)
> 
>  	for (i = 0; i < dev->data->nb_rx_queues; i++) {
>  		rxvq = dev->data->rx_queues[i];
> +		/* Flush the old packets */
> +		virtqueue_flush(rxvq->vq);
>  		virtqueue_notify(rxvq->vq);
>  	}
> 
> diff --git a/drivers/net/virtio/virtio_rxtx.c
> b/drivers/net/virtio/virtio_rxtx.c
> index 609b413..f5b6f94 100644
> --- a/drivers/net/virtio/virtio_rxtx.c
> +++ b/drivers/net/virtio/virtio_rxtx.c
> @@ -80,7 +80,7 @@ virtio_dev_rx_queue_done(void *rxq, uint16_t offset)
>  	return VIRTQUEUE_NUSED(vq) >= offset;
>  }
> 
> -static void
> +void
>  vq_ring_free_chain(struct virtqueue *vq, uint16_t desc_idx)
>  {
>  	struct vring_desc *dp, *dp_tail;
> diff --git a/drivers/net/virtio/virtqueue.c
> b/drivers/net/virtio/virtqueue.c
> index 9ad77b8..c3a536f 100644
> --- a/drivers/net/virtio/virtqueue.c
> +++ b/drivers/net/virtio/virtqueue.c
> @@ -59,3 +59,28 @@ virtqueue_detatch_unused(struct virtqueue *vq)
>  		}
>  	return NULL;
>  }
> +
> +/* Flush the elements in the used ring. */
> +void
> +virtqueue_flush(struct virtqueue *vq)
> +{
> +	struct vring_used_elem *uep;
> +	struct vq_desc_extra *dxp;
> +	uint16_t used_idx, desc_idx;
> +	uint16_t nb_used, i;
> +
> +	nb_used = VIRTQUEUE_NUSED(vq);
> +
> +	for (i = 0; i < nb_used; i++) {
> +		used_idx = vq->vq_used_cons_idx & (vq->vq_nentries - 1);
> +		uep = &vq->vq_ring.used->ring[used_idx];
> +		desc_idx = (uint16_t)uep->id;
> +		dxp = &vq->vq_descx[desc_idx];
> +		if (dxp->cookie != NULL) {
> +			rte_pktmbuf_free(dxp->cookie);
> +			dxp->cookie = NULL;
> +		}
> +		vq->vq_used_cons_idx++;
> +		vq_ring_free_chain(vq, desc_idx);
> +	}
> +}
> diff --git a/drivers/net/virtio/virtqueue.h
> b/drivers/net/virtio/virtqueue.h
> index 9c4f96d..11059fb 100644
> --- a/drivers/net/virtio/virtqueue.h
> +++ b/drivers/net/virtio/virtqueue.h
> @@ -304,6 +304,9 @@ void virtqueue_dump(struct virtqueue *vq);
>   */
>  struct rte_mbuf *virtqueue_detatch_unused(struct virtqueue *vq);
> 
> +/* Flush the elements in the used ring. */
> +void virtqueue_flush(struct virtqueue *vq);
> +
>  static inline int
>  virtqueue_full(const struct virtqueue *vq)
>  {
> @@ -312,6 +315,8 @@ virtqueue_full(const struct virtqueue *vq)
> 
>  #define VIRTQUEUE_NUSED(vq) ((uint16_t)((vq)->vq_ring.used->idx - (vq)-
> >vq_used_cons_idx))
> 
> +void vq_ring_free_chain(struct virtqueue *vq, uint16_t desc_idx);
> +
>  static inline void
>  vq_update_avail_idx(struct virtqueue *vq)
>  {
> --
> 2.7.4