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

[Tiwei Bie <tiwei.bie@intel.com>]

Hi Jens,

On Wed, Aug 30, 2017 at 11:13:06AM +0200, Jens Freimann wrote:
> Hi Tiwei,
> 
> On Tue, Aug 29, 2017 at 04:26:01PM +0800, Tiwei Bie wrote:
> > After starting a device, the driver shouldn't deliver the
> > packets that already existed in the device before it is
> > started to the applications. 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>
> > ---
> > drivers/net/virtio/virtio_ethdev.c |  6 ++++++
> > drivers/net/virtio/virtio_rxtx.c   |  2 +-
> > drivers/net/virtio/virtqueue.c     | 25 +++++++++++++++++++++++++
> > drivers/net/virtio/virtqueue.h     |  5 +++++
> > 4 files changed, 37 insertions(+), 1 deletion(-)
> 
> why don't we flush Tx queues as well?
> 

The elements in the used ring of Tx queues won't be delivered
to the applications. They don't contain any (packet) data, and
will just be recycled during Tx. So there is no need to flush
the Tx queues.

> > 
> > diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
> > index e320811..6d60bc1 100644
> > --- a/drivers/net/virtio/virtio_ethdev.c
> > +++ b/drivers/net/virtio/virtio_ethdev.c
> > @@ -1737,6 +1737,12 @@ virtio_dev_start(struct rte_eth_dev *dev)
> > 		}
> > 	}
> > 
> > +	/* Flush the packets in Rx queues. */
> > +	for (i = 0; i < dev->data->nb_rx_queues; i++) {
> > +		rxvq = dev->data->rx_queues[i];
> > +		virtqueue_flush(rxvq->vq);
> > +	}
> > +
> 
> A little bit further down is a for loop going over rx queues calling
> notify. Could we flush directly before the notify and save the
> additional loop?
> 

I saw there is also another `for' loop to dump the Rx queues.
And I think it makes the code more readable to flush the Rx
queues in a separate `for' loop too. Besides, this function
isn't performance critical. So I didn't combine them into one
`for' loop.

Best regards,
Tiwei Bie